Field of the Invention.
The present invention relates to radiopharmaceutical imaging of the brain, in
particular to dopamine transporter imaging of the striatum (or a portion thereof). A
method of imaging to permit calculation of left : right striatum uptake ratios is
provided, and the degree of asymmetry used to assist in the diagnosis of neurological
diseases. Also provided are a method of diagnosis, method of patient selection, and
method of therapy monitoring using the imaging method, and software tools for use in
the method.
Background to the Invention.
Dopamine transporter imaging radiopharmaceuticals and brain imaging using such
imaging agents have been described extensively in the art since the early 1990s.
Laruelle et al [J.Cereb.Blood Flow Metab., 14, 982-984 (1994)] used the agent 1 I-b-
CIT and a ratio of striatal-to-background activity to give a figure proportional to
dopamine transporter density.
Tatsch et al [Quart. J.Nucl.Med., 56(1), 27-38 (2012)] have reviewed approaches to
the quantification of dopaminergic brain images. They note that ratios are normally
calculated between the specific uptake of the radiopharmaceutical in the target region
(e.g. stratum, caudate, putamen or subregions), and the uptake in a reference area (e.g.
the cerebellum or other suitable region). The reference area represents non-specific
binding of the radiopharmaceutical, and is this chosen for having either an absence or
negligible number of specific tracer binding sites:
SBR = (count density target ROI - count density reference ROD
count density reference ROI
where:
SBR = specific bind ratio or striatum binding ratio,
ROI = region of interest.
Neumeister et al [Psycho log.Med, 3J_(8) 1467-1473 (2001)] study the dopamine
transporter using the radio iodinated tropane 1 I- -CIT in patients with seasonal
affective disorder. Ratios between mean counts in the striatum and cerebellum were
calculated. The cerebellum was used as the reference region because the dopamine
transporter (DaT) density there was known to be low, and hence the cerebellum was
assumed to represent non-specific bound radioactivity as well as free radioactivity.
Lauer et al [J.Neural Transm., 108(6), 661-670 (2001)] studied human schizophrenia
human patients and controls with PET imaging using the glucose metabolism
radiotracer [1 F]-FDG, and the dopamine storage radiotracer [1 F]-FDOPA. Since the
radioactive doses used were different for the patients and controls, left/right ratios of
the hemispheres and frontal cortices were calculated for the [1 F]-FDG scans to permit
comparison of patients with control data from the literature. A higher degree of [ F]-
FDOPA asymmetry was reported for one patient compared to another two, but no
comparison with normal subjects was reported for [1 F]-FDOPA.
Nakagawa et al [Ann.Nucl.Med., 19(4), 267-275 (2005)] studied parkinsonism
patients with 1 F-FDG and the striatal D2 receptor tracer C-raclopride. In order to
obtain specific D2 receptor binding, they subtracted cerebellar activity from the
striatal radioactivity counts. L/R asymmetry of [1 F]-FDG was compared with L/R
asymmetry of 1'C-raclopride in patients. No comparison for either tracer in normal
subjects was performed.
Cai et al [Neural Regen.Res., 5(2), 92-97 (2010)] studied the effect of levodopa on
dopaminergic neurons in animals using the dopamine transporter imaging
radiopharmaceutical Tc-TRODAT-l . They calculated a left/right ratio of specific
uptake ratio after surgical intervention based on animal sacrifice and counting of
tissue samples. The animal control group had been subjected to sham surgery and
were not a true normal dataset.
Gleave et al [Nucl.Med.Biol., 38(5), 741-749 (201 1)] studied the dopamine
transporter imaging radiopharmaceutical 1 I-altropane in an animal model of
Parkinson's disease. Gleave et al calculated an "altropane ratio" of the left to right
side based on animal sacrifice, and tissue sample counting with subtraction of
cerebellum uptake from the striatal counts, to give specific uptake, before calculation
of the left/right ratio. The left / right ratios were compared with animal behaviours,
but no comparison with a normal control was performed.
For dopamine transporter imaging with 1 I-ioflupane, Soderlund et al [J.Nucl.Med.,
54(5), 714-722 (2013)] advocate a combined approach based on: (i) visual assessment
of patient scans, (ii) semi-quantitative assessment based on SBR (based on striatum
uptake with occipital cortex uptake as the reference region), and CPR (caudate-toputamen
ratio). They suggest that this reduces intra-observer variability.
Correction factors may be needed to permit comparison of SBR and similar ratios
obtained using different camera systems within a single imaging facility and between
different sites. Associated software tools have been studied extensively. These are
discussed by Zaknun et al [Quart,J.Nucl.Med.Mol.lmagmg, 5J_, 194-203 (2007)] and
Tatsch et al (vide supra).
Katzenschlager et al [Ann.NeuroL, 53(4), 489-496 (2003)], Zijlmans et al [Movement
Dis., 22(9), 1278-1285 (2007)] and Contrafatto et al [Clin.Neuropharmacol, 34(2),
71-73 (201 1)] have proposed a 'striatal asymmetry index' (SAI) to establish the
degree of asymmetry of DaTSCAN™ uptake, where:
SAI = Y-Z x 2 x l00
(Y+Z)
where Y & Z are the striatal binding indexes (SBIs) for the 2 different sides.
The SBI is calculated from the ipsilateral (same side) caudate and putamen ROI
radioactivity counts, using the algorithm:
SBI = (ROI caudate + ROI putamen) - O
O
where O = mean counts per pixel in the occipital cortex (background).
The striatal asymmetry index (SAI) is thus still based on the background subtraction
approach of the SBR (see above). The papers mention SAI ranges for normals, but
there is no systematic discussion of the width of that range or how it may be affected
by e.g. age. SAI ranges between different cohorts of patients are compared, but the
discussion does not address left/right symmetry (or lack of symmetry) and the
comparison with normal subjects. The SAI is largely used to look at subjects with
symptoms in their left or right side, and the authors attempt to find associations
between the SAI and these symptoms.
It is conventional in the art to compare the patient image with age-matched controls,
since it is known that the striatal uptake of a dopamine transporter
radiopharmaceutical declines with age. Such comparison requires the use of normal
image databases. Such databases are, however, only really meaningful for a coherent
set of data, which may well mean the same camera, same software, same imaging
protocol etc.
There is therefore still a need for dopamine transporter imaging methodology which is
robust enough to give comparable results across a range of camera types, and avoids
the large spread of data seen in multi-site studies, which is statistically sound, and is
suitable for any age of patient.
The Present Invention.
In dopamine transporter radiopharmaceutical imaging, when uptake of the
radiopharmaceutical in the brain is quantified, the values obtained vary significantly
depending on the camera configuration and set-up, image acquisition parameters, and
many other factors. It has therefore so far proved impossible to establish a
meaningful normal database that is built on data from more than one camera type,
without considerable effort to apply 'correction factors'.
In the current GE Healthcare product 'DaTQUANT™, normal data from non-GE
cameras is removed from the data set before calculating. In the Hermes BRASS
product, correction factors are applied but this significantly compromises the utility
and applicability of the 'normal' average values reported.
The present invention is based on the observation that left : right symmetry of
striatum uptake in the normal patient population is maintained independent of the age
and gender of the patient. This symmetrical left/right striatum uptake is shown to be
independent of camera type and image acquisition parameters, and is proposed as a
more robust way to generate both a normal database and patient comparator data -
wherein imaging data can be compared without the need for complex correction
factors.
Visual assessment of dopamine transporter radiopharmaceutical images is generally
used to determine whether brain uptake patterns are normal or abnormal.
Quantification of DaTSCAN™ uptake in the striatum (putamen and caudate
separately and in sum) and comparison with average values obtained from a normal
population has been proposed as a more sensitive and more reproducible method of
detecting abnormal (reduced) uptake suggestive of Parkinson's disease (PD) and
Parkinsonian Syndromes.
A problem with this method is that average striatum binding ratio (SBR) and related
values vary significantly between camera types, and even between the same camera
type at different clinical sites - even when the same radiopharmaceutical is used. The
reason for such a wide variation is not yet fully understood, but factors such as
collimator type and image reconstruction methodology have been suggested. The
consequence is that the 'average' value of SBR cannot easily be transferred from one
site to another as a comparator for the subject. A normal database that is constructed
with data from more than one site shows a very wide spread of values for average
SBR and associated regions of interest, such as entire striatum, putamen or caudate.
Furthermore the standard deviation of 'normal' SBR even from a single site and
camera is large - due to the natural variation within the normal human population. If
the data set includes data from multiple cameras/sites, then the statistical variation
becomes wider still. The effect is that a subject with e.g. early PD and a relatively
low level of reduced striatal uptake may lie within the apparently 'normal' population
of such a data set (i.e. within 1 to 2 standard deviations of the mean value), when a
more statistically robust, coherent normal data set would have flagged the deviation
from normal uptake.
The present invention is based on an analysis of left-right symmetry of striatal uptake.
Surprisingly, the left-right symmetry of such uptake has been found to be maintained
in healthy subjects irrespective of subject age and gender. Thus, for a normal
population, the ratio left striatum: right striatum (absolute or SBR) is close to 1.0 with
low standard deviation. This has been found to hold true even when patient image
data from different clinical sites and/or different camera systems are used.
Furthermore, it is not necessary to apply any correction factors for different cameras
employed in multi-centre datasets, as the symmetry is 'self-calibrating' for each
image.
In neurological disorders where there is loss of dopaminergic function, one side is
usually more affected than the other and the leftright ratio drifts away from 1.0.
Comparison of the leftright ratio with that of the normal population therefore gives a
way to assess whether a subject has abnormal uptake compared to a normal
population that is independent of camera set up and site. This is expected to be
especially valuable in earlier stages of such disease, when a deviation in the leftratio
for the patient compared to the normal population may be detected while the SBR and
similar ratios remain within the normal range (due to the much larger standard
deviation of SBR as described above). This is expected to improve accuracy and
sensitivity and also to facilitate earlier diagnosis of disease. It will also permit earlier
differentiation of PD/PS and Lewy Body Dementia diseases from other disorders with
similar clinical symptoms e.g. ET, AD, vascular and drug-induced PS.
A further advantage is that when comparing leftright uptake values, absolute values
can be used rather than comparing targetbackground ratios. That eliminates the need
for more complex calculations, and reduces statistical variation due to subtraction of
two numbers, each having an associated error bar. This is particularly important with
respect to the counts in the background/reference region. Those counts will be
intrinsically low - hence the error bar or "noise" is relatively large. Furthermore, the
conventional SBR calculates two ratios, so the error bar is compounded by the
calculation. Subtraction of such a figure therefore introduces a statistical variation.
Differences introduced through variations in background in left and right hemispheres
are thereby avoided, and an even narrower distribution of the normal data can be
expected.
Furthermore, the method of the present invention does not require analysis to carry
out comparison with age-matched and gender-matched patients/controls. That is
because the striatum L/R ratio is close to 1.0 in normal subjects regardless of age and
gender. This is a useful simplification. Furthermore, whereas the diagnostic
'dynamic range' of SBR is decreased in patients of advanced age due to the natural
reduction of striatal uptake even in normal subjects, this limitation is not present when
comparing lefhright uptake.
Detailed Description of the Invention.
In a first aspect, the present invention provides a method of imaging useful in the
diagnosis of neurological disease, which comprises:
(i) provision of a subject previously administered with a radiopharmaceutical
suitable for imaging dopamine function;
(ii) assessing the uptake of said radiopharmaceutical in an equivalent region of:
(A) the left; and
(B) the right;
of the striatum of the brain of said subject;
(i) calculating the ratio of the uptake in the equivalent left and right
striatum region from step (ii);
(ii) comparing the ratio for said subject from step (iii) with a normal range
of such ratios for normal subjects.
By the term "method of imaging" is meant a method which generates images of the
subject - typically two-dimensional or three-dimensional, in colour or black and white,
preferably colour. The images may be of the whole subject or a part thereof, i.e. a
region of interest (ROl). For the present invention, the ROl is suitably the brain of the
subject or a region within said brain.
By the term "neurological disease" is meant a disorder with pathological features
affecting brain function such as dementia, movement disorders or drug-induced
disorders of the human or mammalian body. These include, but are not limited to:
Parkinson's disease; Parkinson's syndromes (progressive supranuclear palsy, multiple
system atrophy, corticobasal degeneration); Lewy body dementia (DLB); Alzheimer's
disease and AD-HD. The unequivocal diagnosis of these during life can be difficult,
due to overlapping symptoms of other diseases such as Essential Tremor, Alzheimer's
disease and drug induced or vascular Parkinsonism. Hence, understanding whether
the symmetry of equivalent left and right regions of the brain has been maintained is
still useful. This is described more fully in the second aspect (below).
By the term "subject" is meant a mammal in vivo, preferably the intact mammalian
body in vivo, and more preferably a living human subject. The term "normal range" is
as defined in the second aspect (below).
The term "radiopharmaceutical" has its' conventional meaning, and refers to an
imaging agent wherein the imaging moiety is a radioisotope. The
radiopharmaceutical is labelled with a radioisotope suitable for medical imaging in
vivo. By the term "imaging agent" is meant a compound suitable for imaging the
mammalian body. Such imaging agents are designed to have minimal
pharmacological effect on the mammalian subject to be imaged. Preferably, the
imaging agent can be administered to the mammalian body in a minimally invasive
manner, i.e. without a substantial health risk to the mammalian subject when carried
out under professional medical expertise. Such minimally invasive administration is
preferably intravenous administration into a peripheral vein of said subject, without
the need for local or general anaesthetic.
By the term "dopamine function" is meant imaging dopaminergic neurons of the
midbrain, in particular: dopamine synthesis; dopamine storage and dopamine
reuptake. These are assessed by the following types of radiopharmaceutical
respectively:
(i) a DOPA decarboxylase activity radiopharmaceutical;
(ii) a VMAT2 binding radiopharmaceutical;
(iii) a dopamine transporter binding radiopharmaceutical.
For further details see Nikolaus et al, [Rev.Neurosci., 18, 439-472 (2007)] and Hefti
et al [PET Clin., 5, 75-82 (2010)]. The dopamine function is preferably presynaptic
dopamine function.
The term "DOPA decarboxylase activity radiopharmaceutical" refers to radiotracers
which show the metabolism of the drug DOPA (Z-3,4-dihydroxyphenylalanine).
Such tracers may be DOPA itself labelled with 1 F (1 F-DOPA also known as 1 FFDOPA),
or C ( C-DOPA), or analogues thereof. These are described by Elsinga
et al [Curr.Med.Chem., 13, 2139-2153 (2006)]. The synthesis of 1 F-FDOPA is
described by Kao et al [Ann.Nucl.Med., 25(5), 309-316 (201 1)].
The abbreviation "VMAT2" refers to the vesicular monoamine transporter type 2.
The term "VMAT2 binding radiopharmaceutical" refers to a radiopharmaceutical
suitable for imaging VMAT2. Suitable such radiopharmaceuticals include
dihydrotetrabenazine compounds labelled with C or 1 F, such as [ C]-
dihydrotetrabenazine ([ C]DTBZ) [Hefti et al, PET Clin., 5(1), 75-82 (2010)]. An
automated synthesis of C-DTBZ is described by Zhang et al [Molecules, 17(6),
6697-6704 (2012)]. 1 F-fluoroalkyl dihydrotetrabenazine derivatives are described by
Kilbourn et al [Nucl.Med.Biol., 34(3), 233-237 (2007)], Goswami et al
[Nucl.Med.Biol, 33(6), 685-694 (2006)] and Jahan et al [EJNMMI Res., 1(1), 1-13
(2013)]. A preferred such radiopharmaceutical is the PET radiotracer [1 F]AV-133
[(+)-2-Hydroxy-3-isobutyl-9-(3-fluoropropoxy)-10-methoxy-l,2,3,4,6,7-hexahydro-
1lbH-benzo[a]quinolizine:
[1 F]AV-133
[1 F]AV-133 is described by Hefti et al [PET Clin., 5(1), 75-82 (2010)]. Zhu et al
describe an improved synthesis of [1 F]AV-133 [Nucl.Med.Biol., 37(2), 133-141
(2010)].
The term "dopamine transporter radiopharmaceutical" has its' conventional meaning
in the field of radiopharmaceutical imaging. It refers to an imaging agent for the pre
synaptic dopamine transporter system in vivo, also known as the dopamine reuptake
system. The dopamine transporter system is described by Elsinga et al
[Curr.Med.Chem., 13, 2139-2153 (2006)], as well as in Dopamine Transporters:
Chemistry, Biology, and Pharmacology [Trudell et al (Eds), Wiley-Blackwell (2008)].
Dopamine transporter radiopharmaceuticals have been reviewed by Shen et al
[J.Biomed.BiotechnoL, Article 259349 (2012)], and Wang et al J.Biomed.BiotechnoL,
Article 412486 (2012)].
The phrase "assessing the uptake" refers to techniques for detecting the radioactive
emissions from the radiopharmaceutical within the subject. This is suitably carried
out using a gamma camera or positron emission camera as is known in the art. In the
present method, the uptake measured is preferably the absolute uptake - without
background correction or background subtraction being carried out. The uptake is
also measured for the left and right 'equivalent region' concurrently, and for a defined
period of time - i.e. the same acquisition start time and finish time.
By the phrase "without background correction" is meant that the absolute uptake in
the 'equivalent region' is used directly in the ratio calculation. Thus, no subtraction to
remove counts from a reference region of the patient's brain or other tissues (e.g. to
seek to remove or compensate for non-specific uptake), is carried out. This is a
significant difference over the prior art, where such subtraction is the conventional
wisdom.
The term "striatum" has its conventional meaning, and refers to a subcortical part of
the brain. The striatum is divided into two sectors: the caudate nucleus and putamen,
which are divided by a white matter tract called the internal capsule.
The terms "left" and "right" follow conventional clinical practice and refer to the
patient's left side, and the patient's right side respectively. In medical tomographic
imaging, it is conventional to view two-dimensional images which display horizontal
'slices' of the uptake of the radiopharmaceutical at various positions within the
patient's brain. In the images of the brain, these tomographic slices each have a left
and a right side corresponding to the subject's left and right side and left and right
hemisphere of the brain. Brain tomographic imaging is described in Functional
CerebralSPECT and PET Imaging [Van Heertum et al (eds), 4th Edition, Lippincott
Williams and Wilkins (2009)], and Neuroimaging in Dementia [Barkhof et al,
Springer (201 1)].
By the term "equivalent region" is meant a region of the same volume (for 3-
dimensional imaging) or the same area (for 2-dimensional imaging), on the left and
right side of the brain. This could be as an area of interest (AOI), volume of interest
(VOI) or region of interest (ROI). Software tools are known in the art to assist in such
methodology. Such software tools are commercially available - typically from the
commercial supplier of the gamma camera or positron camera. Other such software
tools are described by Tatsch et al [Quart.J.Nucl.Med., 56(1), 27-38 (2012)].
The size of the 'equivalent region' is up to the size of the whole striatum or a portion
thereof. The person skilled in the art will know that the minimum such 'equivalent
region' chosen will be dictated by good counting statistics - i.e. where the radioactive
counts detected are well above general background. This is governed by variables
such as: the amount of radioactivity administered; the emission characteristics of the
radioisotope; the sensitivity of the camera; the acquisition time, the radius of rotation
of the detectors on certain cameras etc. Consequently, direct comparison of the two
uptake figures (left and right), is representative of the relative uptake in the left and
right striatum. It does not matter whether one calculates A/B (i.e. left/right) or B/A
(i.e. right/left) ratio - as long as a consistent approach is taken. The ratio calculated in
the present method thus provides a measure of left/right asymmetry in the subject
image.
The terms "comprising" or "comprises" have their conventional meaning throughout
this application and imply that the agent, composition or method must have the
essential features, components or steps listed, but that others may be present in
addition. The term 'comprising' includes as a preferred subset "consisting essentially
of which means that other features or components are excluded, i.e. only those listed
are present.
The method of the first aspect may be carried out on the same subject on one or more
occasions, i.e. at different time intervals. Multiple such determinations on the same
subject permit the longitudinal monitoring of a neurological disease, i.e. of disease
progression. This can be carried out with or without therapy. The former is described
as the fourth aspect (below).
Preferred embodiments.
In method of the first aspect, the radioisotope of the radiopharmaceutical is preferably
suitable for either PET or SPECT imaging in vivo. PET imaging
radiopharmaceuticals are often also termed 'radiotracers'. The radioisotope can be
metallic (i.e. a radiometal), or a non-metal. When the imaging moiety is a radiometal,
suitable radiometals can be either positron emitters such as 4Cu, 4 V, 5 Fe, 55Co,
4mTc or Ga; g-emitters such as mTc, In, 11 mIn, or Ga. Preferred radiometals
are Tc, 4Cu, Ga and In. Most preferred radiometals are g-emitters, especially
mTc.
When the imaging moiety is a non-metal, it can be a gamma-emitter or a positron
emitter. Gamma-emitting radiohalogens are suitably chosen from 123I , 131 I or 11Br. A
preferred gamma-emitting radioactive halogen is 123I . When the imaging moiety is a
positron-emitting radioactive non-metal, suitable such positron emitters include: C,
1 N , 150 , 1 F, 1 F, 5Br, Br or 1 4I . Preferred positron-emitting radioactive nonmetals
are C, 1 N , 1 F and 1 4I, especially C and 1 F, most especially 1 F.
In the method of the first aspect, the radiopharmaceutical suitable for imaging
dopamine function is preferably a VMAT2 imaging radiopharmaceutical, or a
dopamine transporter imaging radiopharmaceutical, more preferably a dopamine
transporter imaging radiopharmaceutical. The dopamine transporter
radiopharmaceutical preferably comprises a radio labelled tropane, and more
preferably comprises a 3-phenyltropane. The term "tropane" has its conventional
meaning in the art. PET tropanes have been reviewed by Riss et al
[J.Lab.Comp.Radiopharm., 56(3-4), 149-158 (2013)], and Elsinga et al
[Curr.Med.Chem., 13, 2139-2153 (2006)]. SPECT tropanes have been reviewed by
Wang et al [J.Biomed.Biotechnol, Article 412486 (2012)].
The dopamine transporter radiopharmaceutical preferably comprises a radioisotope
chosen from 1 I or mTc for SPECT, or 1 F or 1 C for PET, more preferably 1 I or
1 F. The dopamine transporter radiopharmaceutical preferably comprises: 1 Iioflupane
(DaTSCAN™), 1 F-ioflupane, 1 I-Altropane, 1 I-PE2I, C-PE2I, 1 I-IPT,
1 I-P-CIT, 1 F-P-CFT, mTc- TROD AT or mTc-technepine. More preferably, the
dopamine transporter radiopharmaceutical comprises 1 3I-ioflupane (DaTSCAN ί ),
1 F-ioflupane or 1 I-Altropane, most preferably 1 I-ioflupane (DaTSCAN™) or 1 IAltropane,
with 1 I-ioflupane (DaTSCAN™) being the ideal.
The structures of these agents are given by Shen et al (J.Biomed.BiotechnoL, Article
259349 (2012)], and are shown in Scheme 1 below:
iSp-FP-CIT
Scheme 1: tropane-based DaT agents.
In step (ii) of the method of the first aspect, "assessing the uptake" is preferably based
on the absolute uptake as described above. The method of the first aspect preferably
excludes further analysis to carry out comparison with age-matched and gendermatched
patients/controls, or to correct for camera type.
In a tomographic image, the striatum appears comma-shaped - with the caudate as the
dot/ball-shaped part of the comma, and the putamen as the tail of the comma. In the
method of the first aspect, the equivalent region of step (ii) is preferably chosen from:
(a) the whole striatum;
(b) the caudate;
(c) the putamen; or
(d) combinations thereof.
It is more preferred that the equivalent region of step (ii) is the putamen, and most
preferred the posterior putamen. That is because the caudate exhibits the highest
uptake, even in Parkinson's syndrome patients - whereas putamen uptake tends to
decline with the progression of Parkinson's diseases. Thus, the putamen is most
likely to be the first to show asymmetric uptake, in particular the posterior putamen.
Hence, using a left/right ratio based on putamen uptake is the most sensitive indicator
of PD, and may permit early diagnosis - before perhaps clinical symptoms become
evident.
It is most preferred that the equivalent region of step (ii) is the combination of all the
following:
(a) the whole striatum;
(b) the caudate;
(c) the putamen;
(d) the posterior putamen.
such that ratios for each of these regions are determined. That is expected to give
more useful diagnostic information.
In the method of the first aspect, the assessing of step (ii) and/or the calculating of
step (iii) is preferably carried out via tomographic imaging, more preferably positron
emission tomography (PET) or single photon emission tomography (SPECT).
The method of the first aspect preferably further comprises one or more of the
following:
(I) calculating a caudate:putamen or putamen:caudate ratio for the left and
right striatum separately;
(II) calculating a striatal binding ratio (SBR; as defined above) for left and
right hemisphere;
(III) calculating the ratio of counts in equivalent left and right regions of the
brain;
(IV) comparing leftright (or rightleft) ratios obtained in (III) with normal
values.
This additional data complements the striatum binding ratio, and is particularly useful
in the further clinical diagnosis of patients where said ratio may appear 'normal', but
the asymmetry compared to the normal population, clinical symptoms or other criteria
suggest a neurological disease. See the discussion in the second aspect (below).
The dopamine transporter radiopharmaceuticals of the first aspect can be obtained as
follows. DatScan ί (1 3I-ioflupane) is commercially available in Europe and the USA
from GE Healthcare. Other agents can be prepared via the methods cited above, as
well as the references cited by Shen et al [J.Biomed.Biotechnol, Article 259349
(2012)], andNikolaus et al, [Rev.Neurosci., 18, 439-472 (2007)].
In a second aspect, the present invention provides a method of diagnosis which
comprises the method of imaging of the first aspect, where the comparing of step (iv)
is with a database of such ratios, wherein said database contains such ratios for normal
subjects; and which further comprises:
(v) when the ratio from step (iv) is within the normal range, said subject is
classified as having a normal presentation;
(vi) when the ratio from step (iv) is outside the normal range, the patient is
classified as suffering from a neurological disease.
Preferred embodiments of the method of imaging and the radiopharmaceutical
suitable for imaging presynaptic dopamine function in the method of diagnosis of the
second aspect, are as described in the first aspect (above).
The database of step (iv) of the second aspect suitably comprises the ratio of step (iii)
for a group of normal subjects, and preferably further comprises such ratios for
patients having a known, defined neurological condition. An important advantage of
the present invention is that such ratios can readily be compiled from a range of
clinical datasets, even if collected on different cameras, without the need for
correction factors. This facilitates the compilation of a larger, usable dataset - which
in turn means the data within the database carries a more powerful statistical
significance. The database comparison is suitably carried out using the software tool
of the fifth aspect.
The term "normal range" refers to the uptake ratio of the first aspect for the normal
subjects within the database. The ordinary person skilled in art can choose a suitable
confidence limit, but a 95% confidence limit corresponding to approximately ±2
standard deviations of the mean from the normal range, is often selected.
By the term "normal presentation" is meant that the left/right ratio determined for the
subject under diagnosis is within the normal range. This indicates that, either the
subject is normal, or that the patient is suffering from a neurological condition which
exhibits a symmetric pattern. Thus, certain neurological conditions exhibit a 'normal'
striatum left/right ratio, i.e. close to 1.0.
In the method of the second aspect, neurological diseases where the left/right ratio of
step (iii) is expected to fall outside the normal range (i.e. show left/right asymmetry)
are: Parkinson's disease or Parkinson's syndromes such as Multiple System Atrophy
(MSA) and Progressive Supranuclear Palsy (PSP).
In the method of the second aspect, examples of neurological diseases where the
left/right ratio of step (iii) is expected to fall within the normal range (i.e. show
left/right symmetry) are: drug-induced parkinsonism, vascular pseudo-parkinsonism,
Alzheimer's disease, essential tremor (ET) and DLB.
The finding of a "normal presentation" can be used to exclude certain neurological
conditions which do exhibit an asymmetric ratio, and thus differentiate PD, MSA and
PS for such subjects. In combination with the subject's other clinical symptoms,
and/or further medical imaging or testing, this information may still be valuable in
patient diagnosis and management. Thus, e.g. Contrafatto et al have shown that the
SAI (as defined above) can be used to differentiate Parkinson's disease from vascular
parkinsonism [Acta Neurol. Scand., 126(1), 12-16 (2012)]. Furthermore, for DLB, the
striatum left/right ratio is expected to show a 'normal presentation' but further
analysis, in particular determination of the SBR is expected to be valuable - since the
SBR is expected to be low for such subjects. The finding of a 'normal presentation'
can then be put into context using other tests, such as additional steps (I)-(IV) of the
first aspect - to seek to finalise the diagnosis.
In a third aspect, the present invention provides a method of selecting or excluding a
subject for a particular therapy of a neurological disease, which comprises the method
of imaging of the first aspect, or the method of diagnosis of the second aspect.
Preferred embodiments of the method of imaging and the radiopharmaceutical
suitable for imaging presynaptic dopamine function in the method of selection of the
third aspect, are as described in the first aspect (above). Preferred embodiments of the
method of diagnosis in the third aspect, are as described in the second aspect (above).
Preferred embodiments of the neurological disease in the third aspect are those
diseases described in the second aspect as showing left/right asymmetry, i.e.
Parkinson's disease or Parkinson's syndromes.
When the method of imaging of the first aspect, or the method of diagnosis of the
second aspect permits a positive diagnosis of a given neurological disease, then the
appropriate therapy for the disease is selected for the subject.
The third aspect also includes excluding from anti-Parkinsonian therapy a subject
shown to have an apparently normal L/R striatal ratio using the methods of the first or
second aspect. This exclusion is important, since it helps avoid misdiagnosis and
unsuitable therapies which cannot benefit the subject, and only risk causing harm.
The third aspect also includes deselecting from therapy a subject already undergoing
therapy for a neurological condition, whose existing course of treatment/therapy, is
found to be unsuitable after the imaging of the first aspect, or the diagnosis of the
second aspect establishes that the treatment/therapy is misdirected due to a previous
misdiagnosis. This is particularly important if e.g. the subject has been misdiagnosed
with PD, and is receiving anti-Parkinson's medication or therapy - but is found by the
method(s) of the invention to be suffering from a different condition.
In a fourth aspect, the present invention provides a method of monitoring the efficacy
of a course of therapy of a neurological disease of a subject, which comprises the
method of imaging of the first aspect, or the method of diagnosis of the second aspect.
Preferred embodiments of the method of imaging and the radiopharmaceutical
suitable for imaging presynaptic dopamine function in the method of monitoring of
the fourth aspect, are as described in the first aspect (above). Preferred embodiments
of the method of diagnosis in the fourth aspect, are as described in the second aspect
(above). Preferred embodiments of the neurological disease in the fourth aspect are
those diseases described in the second aspect as showing left/right asymmetry, i.e.
Parkinson's disease or Parkinson's syndromes.
In a fifth aspect, the present invention provides a software tool suitable for carrying
out:
(a) step (ii) and/or step (iii) of the method of imaging of the first aspect; or
(b) one or more of steps (ii) to (v) of the method of diagnosis of the second
aspect; or
(c) the method of selection of the third aspect; or
(d) the method of monitoring of the fourth aspect; or
(e) combinations of one or more of (a) to (d).
Preferred embodiments of the method of imaging and the radiopharmaceutical
suitable for imaging presynaptic dopamine function in the fifth aspect, are as
described in the first aspect (above). Preferred embodiments of the method of
diagnosis in the fifth aspect, are as described in the second aspect (above).
The software tool of the fifth aspect preferably runs on a personal computer, a gamma
camera or a PET camera workstation.
The software tool of the fifth aspect preferably comprises the database of L/R ratios
described in the second aspect.
In a sixth aspect, the present invention provides the use of the radiopharmaceutical
suitable for imaging presynaptic dopamine function of the first aspect, in one or more
of:
(i) the method of imaging of the first aspect;
(ii) the method of diagnosis of the second aspect;
(iii) the method of selection of the third aspect; or
(iv) the method of monitoring of the fifth aspect.
Preferred embodiments of the method of imaging and the radiopharmaceutical
suitable for imaging presynaptic dopamine function in the sixth aspect, are as
described in the first aspect (above). Preferred embodiments of the method of
diagnosis in the sixth aspect, are as described in the second aspect (above).
In a seventh aspect, the present invention provides the use of the software tool as
defined in the fifth aspect in one or more of:
(i) the method of imaging of the first aspect;
(ii) the method of diagnosis of the second aspect;
(iii) the method of selection of the third aspect; or
(iv) the method of monitoring of the fifth aspect.
Preferred embodiments of the method of imaging and the radiopharmaceutical
suitable for imaging presynaptic dopamine function in the seventh aspect, are as
described in the first aspect (above). Preferred embodiments of the method of
diagnosis in the seventh aspect, are as described in the second aspect (above).
In an eighth aspect, the present invention provides the use of a tomographic imaging
device in one or more of:
(i) the method of imaging of the first aspect;
(ii) the method of diagnosis of the second aspect;
(iii) the method of selection of the third aspect; or
(iv) the method of monitoring of the fourth aspect.
Preferred embodiments of the method of imaging and the radiopharmaceutical
suitable for imaging presynaptic dopamine function in the eighth aspect, are as
described in the first aspect (above). Preferred embodiments of the method of
diagnosis in the eighth aspect, are as described in the second aspect (above).
In a ninth aspect, the present invention provides a database as described in the second
aspect.
Description of the Figures.
In Figures 1 and 2, the solid line shows the mean, and the dotted line the 95%
confidence limit.
Figure 1 shows the prior art SBR determination for normal human subject imaging
data. This shows a considerable spread of values, and a variation with the age of the
subject. Figure 2 shows the striatum L/R ratio calculation for the same data set as
Figure 1.
Figure 3 shows the left and right striatal binding values from the normal data set of
Example 3. The data from Subject 1 of Example 4, a male 79 years old Parkinson's
patient based on clinical diagnosis, (solid circle and triangle, respectively, also
marked by the arrows) are included for comparison. Subject 1 is an illustrative
example. It can be seen that, based on SBR alone, Subject 1' s ratios are within the
normal ranges as indicated by the hollow diamonds and squares.
Figure 4 shows the asymmetry index (or normalised left-right asymmetry) of the
normal data set of Example 3. Subject 1 is illustrative data from Example 5. The data
for Subject 1 (see Figure 3; solid square, pointed out by arrow) is clearly outside the
range given by the normal values (hollow diamonds), hence indicating abnormality of
Subject 1' s DaTSCAN image that would not be obvious when merely studying striatal
binding ratio alone as per Figure 3.
Figure 5 shows the ratio of uptake in the posterior putamen to the caudate for the
normal group, with data for Subject 1 superimposed. The normal range is defined by
the hollow diamonds (left striatum) and hollow squares (right striatum). As seen,
especially the right-hand ratio of Subject 1' s posterior putamen to caudate ratio (solid
triangle, pointed out by arrow) was below the normal range which again suggests
abnormality that is not visible when merely studying striatal binding as in Figure 3.
The invention is illustrated by the non-limiting Examples detailed below. Examples 1
and 2 are theoretical Examples, whereas Examples 2 -5 are based on clinical data.
Example 1 is a comparative Example which shows the calculation of SBR using data
from: (i) a range of camera manufacturers (Group A); (ii) a single manufacturer (GE;
Group B) and (iii) a patient. The variation in Group A is so wide that there is almost
no value in it for comparison with patient data. Even with Group B, the normal range
is too wide to be useful for comparative purposes. This demonstrates the difficulties
with the current methodology.
Example 2 applies the method of the present invention. In the normal population, for
each individual subject the values for left and right are likely very close: a normal
subject with striatum right = 1.78 and striatum left = 3.05 is inconceivable even
though these represent - 1 standard deviation and + 1 standard deviation from the
normal mean respectively. Left and right values both around 1.78, or both around
3.05 are much more likely.
Table 3 of Example 2 shows calculation of the rightleft ratios, showing that the
variation of the ratio for the normal population is indeed much narrower than the
variation of the absolute values and is independent of site and camera type.
Application of correction factors or algorithms that compensate for camera type is
therefore unnecessary.
Example 1 shows that the 'normal' distribution for SBR is very wide (23-24% RSD
i.e. Relative Standard Deviation) and non-uniform across age groups. The ratio SBR
left: SBR right is relatively narrow (4% RSD) and uniform across age groups. The
lefhright ratio of the invention is therefore a more sensitive tool for detecting
deviation from normality.
Example 3 and Figures 3 and 4 show that the L/R asymmetry ratio of the present
invention is stable in the cohort of normal subjects irrespective of age, whereas the
SBR method of the prior art tends to decline with age (from about 3.2 in the thirties
group to about 2.2 in the eighties age group) - necessitating age corrections when data
comparisons are made.
Example 4 shows that, based on SBR alone, 1 subjects were clinically 'abnormal'
but were classified as normal when applying the SBR rules from the normal database.
The result is low sensitivity. Only 2 clinically normal cases were wrongly classified
as abnormal by the SBR method.
Example 5 shows that, when the method of the present invention is used, the number
of wrongly classified clinically abnormal cases reduces from 17 to 5, i.e. 12 subjects
had a changed classification as a result of involving the asymmetry determination.
That is a significant improvement in the correlation of the clinical and imaging
classifications. The use of the asymmetry index also classifies some clinically
'normal' cases as 'abnormal', hence reducing specificity. In that regard, the clinical
standard of truth is not perfect, especially e.g. for subjects that may be converting to
disease but do not as yet show any clinically abnormal symptoms. Hence, it is
possible that the abnormal DaTSCAN result is an early indicator of future abnormal
clinical status even though these subjects do not yet show any clinical symptoms.
Abbreviations.
AD: Alzheimer's disease;
AD-HD: attention deficit hyperactivity disorder;
AOI: area of interest;
DaT: dopamine transporter;
DLB: Lewy body dementia;
DOPA: L- ,4-dihydroxyphenylalanine;
ET: essential tremor;
MSA: Multiple System Atrophy;
NDB: Normal Database;
PET: positron emission tomography;
PD: Parkinson's disease;
PS: Parkinsonian syndromes;
PSP: Progressive Supranuclear Palsy (PSP);
RSD: Relative Standard Deviation, i.e. the standard deviation expressed as a
percentage of the average, RSD = (SD/Mean) x 100%;
SAI: striatal asymmetry index;
SBR: striatum binding ratio;
SD: standard deviation;
SPECT: single photon emission tomography;
VMAT2: vesicular monoamine transporter type 2;
VOL volume of interest.
Example 1: Striatal Binding Ratios: Normal Range (comparative Example).
The European Association of Nuclear Medicine RESEARCH4LIFE© initiative
("EARL") has been compiling a database of DaTSCAN images of normal human
subjects since 2007 (see http://earl.eanm.org/cms/website.php?id=/en/projects/encdat.
htm). The ENCDAT database includes 150 normal subjects - with data from a
range of camera types. SBR was calculated for the 150 normal subjects (Group A):
SBR = (count density target ROI - count density reference ROD
count density reference ROI
where:
SBR = specific binding ratio or striatum binding ratio,
ROI = region of interest.
Brain imaging data for n=37 normal subjects acquired on GE cameras in the
ENCDAT database was used for the calculation of SBR (Group B). SBR for an
illustrative patient from the ENCDAT database is also shown:
Table 1
Figure 1 shows the variation of SBR with age for the normal patient group in the
ENCDAT data set. The 95% confidence interval is shown, and can be seen to be
wide.
Example 2 : Striatal Left/Right Binding Ratio.
Using the method of the present invention, the data from Example 1 was used to
calculate a striatum right:left ratio:
Table 2.
Table 3 below uses SBR data for normal subjects from the ENC DAT database.
Three subjects from each of five different sites are shown, but the overall average is
based on data from 11 sites:
Table 3
where:
Site 1 = Ankara Infinia; Site 2 = Copenhagen IRIX;
Site 3 = Genoa Varicam; Site 4 = Leuven IRIX;
Site 5 = London Infinia;
%RSD = st dev x 100/mean.
Example 3 : Normal Database (NDB).
Two databases of scans of DaTSCAN™ (GE Healthcare Ltd) normal human subjects
were evaluated using:
(i) the SBR method of the prior art (see Example 1), with the occipital cortex
as the reference region;
(ii) the L/R ratio method of the present invention.
The PPMI database was of 122 subjects (age range 31-84; 62% male 38% female).
The ENCDAT database was of 122 subjects (age range 20-82; 52% male 48% female).
The data from all subjects in each decade of life (20s, 30s etc) were averaged. The
results are shown in Figures 3 and 4.
Example 4 : Patient Classification Using NIP and SBR (Comparative Example).
The data from two GE Healthcare Ltd clinical trials of Datscan™:
(i) comparing PD and ET;
(ii) clinically uncertain PD;
104 patients in total were analysed using SBR calculation only. Each determination
was compared with the patient determination based on clinical symptoms. The results
are shown in Table 4 :
Table 4.
Thus, 42 subjects (of the 104) were found to be abnormal on both SBR and clinical
criteria, and 43 normal on both criteria. 17 subjects were classified as clinically
abnormal, but those same subjects were categorised as normal by SBR. Two subjects
were classified as normal on clinical criteria, but those same two subjects were found
abnormal on SBR.
This gives a sensitivity of 71%, specificity of 96% and accuracy of 82% for the SBR
technique. The clinical diagnosis was assumed to be the 'true' diagnosis, and
sensitivity and specificity can then be calculated. Sensitivity = 100 x True Positives /
(True Positives + False Negatives) = 100 x 42/59 = 71%. Specificity = 100 x True
Negatives / (True Negatives + False Positives) = 100 x 43/45 = 96%.
Accuracy = 100 x (True Positives + True Negatives) / Population = 100 x (42 +
43)/104 = 82%.
Example 5: Patient Classification Using NIP and L/R Ratio.
The 104 patient data set from Example 4 was analysed using SBR together with the
L/R asymmetry of the present invention. The results are given in Table 5:
Table 5.
This gives a sensitivity of 92%, specificity of 76% and accuracy of 85% for the SBR
plus asymmetry.

CLAIMS.
1. A method of imaging useful in the diagnosis of neurological disease, which
comprises:
(i) provision of a subject previously administered with a radiopharmaceutical
suitable for imaging dopamine function;
(ii) assessing the uptake of said radiopharmaceutical in an equivalent region of:
(A) the left; and
(B) the right;
of the striatum of the brain o f said subject;
(iii) calculating the ratio of the uptake in the equivalent left and right
striatum region from step (ii);
(iv) comparing the ratio for said subject from step (iii) with a normal range
of such ratios for normal subjects.
2 . The method of claim 1, where the dopamine function is chosen from:
(i) DOPA decarboxylase activity;
(ii) VMAT2 binding;
(iii) dopamine transporter binding.
3. The method of claim 2, where the radiopharmaceutical is a VMAT2 binding
radiopharmaceutical.
4 . The method of claim 3, where the VMAT2 binding radiopharmaceutical is
1 F-AV-133.
5. The method of claim 4, where the radiopharmaceutical is a dopamine
transporter binding radiopharmaceutical.
6. The method of claim 5, where the radiopharmaceutical comprises a tropane,
and is chosen from: 1 I-iofiupane, 1 F-ioflupane, 1 I-Altropane, 1 I-PE2I, C-PE2I,
1 I-IPT, 1 I-P-CIT, 1 F-P-CFT, mTc- TROD AT or mTc-technepine.
O 2015/011267 PCT/EP2014/066042
7. The method of any one of claims 1 to 6 where the neurological disease is
suspected to be Parkinson's disease, Parkinson's syndromes or Lewy Body Dementia.
8. The method of any one of claims 1 to 7, where the equivalent region of step (ii)
is chosen from:
(a) the whole striatum;
(b) the caudate;
(c) the putamen; or
(d) or combinations thereof.
9. The method of any one of claims 1 to 8, where the assessing of step (ii) and/or
the calculating of step (iii) is carried out via tomographic imaging.
10. The method of any one of claims 1 to 9, which further comprises one or more
of the following:
(I) calculating a caudate:putamen or putamen: caudate ratio for the left and
right striatum separately;
(II) calculating a striatal binding ratio (SBR; as defined above) for left and
right hemisphere;
(III) calculating the ratio of counts in equivalent left and right regions of the
brain;
(IV) comparing leftright (or rightleft) ratios obtained in (III) with normal
values.
11. A method of diagnosis which comprises the method of imaging of any one of
claim 1 to 10, where the comparing of step (iv) is with a database of such ratios,
wherein said database contains such ratios for normal subjects;
and which further comprises:
(v) when the ratio from step (iv) is within the normal range, said subject is
classified as having a normal presentation;
(vi) when the ratio from step (iv) is outside the normal range, the patient is
classified as suffering from a neurological disease.
12. A method of selecting or excluding a subject for a particular therapy of a
neurological disease, which comprises the method of imaging of any one of claims 1
to 10, or the method of diagnosis of claim 11.
13. A method of monitoring the efficacy of a course of therapy of a neurological
disease of a subject, which comprises the method of imaging of any one of claims 1 to
10, or the method of diagnosis of claim 11.
14. A software tool suitable for carrying out:
(a) step (ii) and/or step (iii) of the method of imaging of any one of claims 1 to
10; or
(b) one or more of steps (ii) to (v) of the method of diagnosis of claim 11; or
(c) the method of selection of claim 12; or
(d) the method of monitoring of claim 13; or
(e) combinations of one or more of (a) to (d).
15. The software tool of claim 14, which runs on a personal computer, a gamma
camera or a PET camera.
16. The software tool of claim 14 or 15, further comprising the database of ratios
as defined in claim 11.
17. The use of the radiopharmaceutical suitable for imaging dopamine function as
defined in any one of claims 1 to 6 in one or more of:
(i) the method of imaging of any one of claims 1 to 10;
(ii) the method of diagnosis of claim 11;
(iii) the method of selection of claim 12; or
(iv) the method of monitoring of claim 13.
18. The use of the software tool as defined in any one of claims 14 to 16 in one or
more of:
(i) the method of imaging of any one of claims 1 to 10;
(ii) the method of diagnosis of claim 11;
(iii) the method of selection of claim 12;
O 2015/011267 PCT/EP2014/066042
(iv) the method of monitoring of claim 13.
19. The use of a tomographic imaging device in one or more of:
(i) the method of imaging of any one of claims 1 to 10;
(ii) the method of diagnosis of claim 11;
(iii) the method of selection of claim 12; or
(iv) the method of monitoring of claim 13.
20. A database as defined in claim 11.