Imaging of dopamine transporters with technetium-99m TRODAT-1 and single photon emission computed tomography

Tc-99m TRODAT-1 SPECT is a Potential Biomarker for Restless Leg Syndrome in Patients with End-Stage

Rationales: Restless leg syndrome (RLS) is a common complication in patients with end-stage renal disease (ESRD). However, there is a lack of biomarkers linking uremic RLS to dopaminergic neurons. Previous studies demonstrated that Tc-99m TRODAT-1 SPECT was a biomarker for RLS but the correlation between the physiologic parameter was lacking. Methods: Overall, 32 patients were enrolled in the study and divided into the following 3 groups: (1) control (n = 13), (2) ESRD without RLS (n = 8) and (3) ESRD with RLS (n = 11). All patients had a clinical diagnosis of RLS and received Tc-99m TRODAT-1 SPECT. A subgroup analysis was performed to compare differences between the control and ESRD with RLS groups. Tc-99m TRODAT-1 SPECT was performed and activities in the striatum and occipital areas were measured using manually delineated regions of interest (ROIs) by an experienced nuclear medicine radiologist who was blinded to clinical data. Results: The total ratio of Tc-99m TRODAT SPECT was lower in the ESRD with RLS group (p = 0.046). The uptake ratio of TRODAT negatively correlated with serum parathyroid hormone (r = −0.577, p = 0.015) and ferritin (r = −0.464, p = 0.039) concentrations. However, the uptake positively correlated with the hemoglobin concentration (r = 0.531, p = 0.011). The sensitivity and specificity of the total TRODAT ratio for predicting RLS in the overall population were 95.0% and 67.7%, respectively, at a cutoff value of 0.980 (area under the curve of receiver operating characteristic curve was 0.767, p = 0.024). Conclusion: In patients with ESRD and RLS, Tc-99m TRODAT might be a potential biomarker. Dysregulated hemoglobin, serum parathyroid hormone and serum ferritin concentrations might influence the uptake of the TRODAT ratio.

Phase I clinical study with different doses of 99mTc-TRODAT-1 in healthy adults

OBJECTIVES

To study the pharmacokinetics, biodistribution, and injection doses of ^99mTc-TRODAT-1 in healthy adults.

METHODS

Thirty healthy individuals comprising 15 females and 15 males were randomly divided into three groups and the injection doses of ^99mTc-TRODAT-1 of group 1, 2, and 3 were 370 MBq, 740 MBq, and 1110 MBq, respectively. Assessments of subjective symptoms and tests were performed before and after injection. Blood and urine collections and whole-body planar imaging were analyzed at various time points. Bilateral brain striatal SPECT images obtained at 3.5 h PI were assessed visually and semiquantitatively.

RESULTS

No serious adverse events or deaths were observed in our study. The pharmacokinetic analysis showed that ^99mTc-TRODAT-1 was eliminated rapidly from the circulation, with just about 4% of the injected dose remaining in blood at 1 h post-injection. The mean cumulative urinary excretion over 24 h was just 2.96 ± 0.96%ID. The time-activity curve demonstrated that the radioactivity was mainly in liver and abdomen. The highest absorbed dose was in the dose-limiting organ, liver (20.88 ± 4.45 × 10^-3 mSv/MBq). The average effective dose was 5.22 ± 1.05 × 10^-3 mSv/MBq. The clarity of striatal images assessed visually in group 1 was worse than that in group 2 and 3. The semiquantitative analysis showed that there were no differences in striatum/cerebellum between the three groups (group 1: 1.77 ± 0.11, group 2: 1.62 ± 0.14, and group 3: 1.75 ± 0.20; P = 0.088).

CONCLUSIONS

^99mTc-TRODAT-1 was safe to use in humans and showed the status of dopaminergic neurons specifically and clearly. The injection dose we suggested was 740 MBq.

Is the dopaminergic loss associated with gait and postural impairments in subjects with Parkinson's disease at different motor stages?

Gait and postural control deficiencies in Parkinson's disease (PD) involve several specific motor aspects. The aim of this study was to identify and compare the main changes in gait kinematics and postural control with dopaminergic loss in the striatum region. This is a cross-sectional study that included 42 individuals with PD at different motor stages, according to the Hoehn & Yahr scale (H&Y). Motor subsection of the Movement Disorder Society-Unified Parkinson Disease Rating Scale-part III (MDS-UPDRS III) was used to evaluate general motor aspects. Gait kinematics was assessed using a three-dimensional motion capture system. Postural control was assessed by stabilometry using force platforms. Dopamine depletion was verified through 99mTc-TRODAT-1 (SPECT-CT) examination. We included 12, 15 and 15 individuals classified as H&Y I, II and III, respectively. We identified worse values of dopamine transporter uptake, MDS-UPDRS III, gait parameters (velocity, step length and stride length) and center of pressure displacement as the disease progressed. Our results indicate that higher dopaminergic loss and gait and postural control deficits occur between the H&Y levels II and III.

99mTc-TRODAT-1 SPECT as a Potential Neuroimaging Biomarker in Patients With Restless Legs Syndrome

BACKGROUND

Restless legs syndrome (RLS) is a neurological sensory motor disorder of which pathophysiology remains sketchy. The present study was aimed to determine the diagnostic accuracy and potential of SPECT-TRODAT imaging in discriminating patients with RLS from normal individuals.

PATIENTS AND METHODS

A total of 34 subjects, 22 diagnosed with RLS and 12 classified as normal, were enrolled. Brain SPECT images were acquired 180 minutes after IV injection of 740 to 925 MBq (20-25 mCi) 99mTc-TRODAT-1 using a double-headed γ-camera equipped with high-resolution fan-beam collimators. Regions of interest were drawn over the whole striatum, caudate, and putamen nucleus of each hemisphere on composite images of the 9 slices with the highest basal ganglia activity. The brain SPECT 99mTc-TRODAT-1 imaging was compared with early-stage RLS patients and healthy volunteers groups.

RESULT

SPECT imaging in RLS patients showed reduced radioactivity accumulation in the striatum profile. The major abnormal result observed is the significantly reduced uptake in striatal dopamine transporter density and activity. The symmetric striatal uptake was observed, and striatum dopamine transporter destiny was more impaired in patients with RLS disease. SPECT images also showed significant differences between patients and volunteers.

CONCLUSIONS

This study supports that symptoms of restless legs resulted from the striatum of the brain dopaminergic system dysfunction.

Comparison between Different Intensity Normalization Methods in 123I-Ioflupane Imaging for the Automatic Detection of Parkinsonism

Intensity normalization is an important pre-processing step in the study and analysis of DaTSCAN SPECT imaging. As most automatic supervised image segmentation and classification methods base their assumptions regarding the intensity distributions on a standardized intensity range, intensity normalization takes on a very significant role. In this work, a comparison between different novel intensity normalization methods is presented. These proposed methodologies are based on Gaussian Mixture Model (GMM) image filtering and mean-squared error (MSE) optimization. The GMM-based image filtering method is achieved according to a probability threshold that removes the clusters whose likelihood are negligible in the non-specific regions. The MSE optimization method consists of a linear transformation that is obtained by minimizing the MSE in the non-specific region between the intensity normalized image and the template. The proposed intensity normalization methods are compared to: i) a standard approach based on the specific-to-non-specific binding ratio that is widely used, and ii) a linear approach based on the α-stable distribution. This comparison is performed on a DaTSCAN image database comprising analysis and classification stages for the development of a computer aided diagnosis (CAD) system for Parkinsonian syndrome (PS) detection. In addition, these proposed methods correct spatially varying artifacts that modulate the intensity of the images. Finally, using the leave-one-out cross-validation technique over these two approaches, the system achieves results up to a 92.91% of accuracy, 94.64% of sensitivity and 92.65 % of specificity, outperforming previous approaches based on a standard and a linear approach, which are used as a reference. The use of advanced intensity normalization techniques, such as the GMM-based image filtering and the MSE optimization improves the diagnosis of PS.

Correlative (99m)tc-labeled tropane derivative single photon emission computer tomography and clinical assessment in the staging of Parkinson disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by a selective loss of dopamine in the striatum. Problems remain in the accurate diagnosis of PD. The diagnosis of idiopathic PD is based on the interpretation of clinical signs and symptoms could be incorrect at the time of initial presentation. In vivo imaging of the dopaminergic system has the potential to improve the diagnosis of PD in its early stages. The imaging of dopamine transporter (DAT) with ^99mTc-labeled tropane derivative (TRODAT-1) single photon emission computer tomography/computer tomography (SPECT/CT) has been proposed to be a valuable and feasible means of assessment of the integrity of dopamine neurons. The purpose of this study was to investigate the potential usefulness of ^99mTc-TRODAT-1 imaging in the evaluation of patients with PD and classify into different stages of the disease. SPECT imaging with ^99mTc-TRODAT-1 was conducted in 16 consecutive PD patients (9 men; 7 women) and in 6 age matched healthy volunteers (4 men; 2 women). The images were obtained 3 h after the intra-venous injection of the tracer. Specific uptake in the striatum and its sub-regions, including the putamen and caudate nucleus was calculated and the ratios of specific striatal binding to nonspecific occipital binding were calculated. ANOVA with Dunnett C post-hoc analysis was conducted using SPSS 20. A stepwise reduction in specific striatal uptake of ^99mTc-TRODAT-1 with increasing disease severity between healthy control versus Stage I versus Stage II versus Stage III was found in PD patients (i.e., 3.77 vs. 2.56 vs. 1.57 vs. 0.63, P < 0.05). The changes were magnified by measurement of specific putaminal uptake (1.43 vs. 0.79 vs. 0.54 vs. 0.19, P < 0.05) and specific caudate uptake (1.90 vs. 1.47 vs. 0.73 vs. 0.27, P < 0.05). No remarkable adverse reactions were found in either healthy volunteers or PD patients during or after imaging. ^99mTc-TRODAT-1 is accurate and widely available for the assessment of DAT activity, which might shed light on the integrity of the presynaptic nigrostriatal function. Our preliminary study results confirm the potential of using ^99mTc-TRODAT-1 for DAT measurement, which is clinically important for the staging of PD.

Comparison of 99mTc-TRODAT-1 SPECT and 18 F-AV-133 PET imaging in healthy controls and Parkinson's disease patients

(99m)Tc-TRODAT-1 is the first clinical routine (99m)Tc radiopharmaceutical to evaluate dopamine neurons loss in Parkinson's disease (PD). (18)F-AV-133 is a novel PET radiotracer targeting the vesicular monoamine transporter type 2 (VMAT2) to detect monoaminergic terminal reduction in PD patients. The aim of this study is to compare both images in the same health control (HC) and PD subjects.

METHODS

Eighteen subjects (8 HC and 10 PD) were recruited for (99m)Tc-TRODAT-1 SPECT, (18)F-AV-133 PET and MRI scans within two weeks. The SPECT images were performed at 4-h post-injection for 45 min, and the PET images were performed at 90 min post-injection for 10 min. Each PET and SPECT image was normalized into Montreal Neurological Institute template aided from individual MRI for comparison. For regional analysis, volume of interest (VOIs) of bilateral caudate nuclei, anterior, posterior putamen and occipital cortex (as reference region) were delineated from the normalized MRI. The specific uptake ratio (SUR) was calculated as (regional mean counts/reference mean counts-1). The nonparametric Mann-Whitney U test was used to evaluate the power of differentiating control from PD subjects for both image modalities. The correlations of the SURs to the clinical parameters were examined. For voxelwise analysis, two-sample t-test for group comparison between HC and PD was computed in both image modalities.

RESULTS

The SURs of caudate nucleus and putamen correlated well between two image modalities (r = 0.81, p<0.001), and showed significant different between HC and PD subjects. Of note, the (18)F-AV-133 SUR displayed a better correlation to PD clinical laterality index as compared to (99m)Tc-TRODAT-1 (r = 0.73 vs. r = 0.33). Voxelwise analysis showed more lesions for PD subjects from (18)F-AV-133 image as compared to (99m)Tc-TRODAT-1 especially at the substantia nigra region.

CONCLUSION

(18)F-AV-133 PET demonstrated similar performance in differentiation PD from control, and a better correlation to clinical characteristics than that of (99m)Tc-TRODAT-1 SPECT. (18)F-AV-133 PET also showed additional information in substantia nigra integrity in PD subjects by voxelwise analysis. Collectively, (18)F-AV-133 could be a promising and better tracer for clinical use to detect monoaminergic terminal reduction in PD patients.

Reproducibility of brain dopamine transporter binding with Tc-99m TRODAT-1 SPECT in healthy young men

Single photon emission computed tomography (SPECT) with Tc-99m TRODAT-1 as ligand can be used to evaluate striatal dopamine transporters (DAT) in young subjects. The purpose of this study was to evaluate the reproducibility of (99m)Tc-TRODAT-1 SPECT in DAT binding in healthy young men. Fourteen healthy young men were recruited. The test-retest studies were performed 1week apart. Specific uptake ratios (SUR) of the striatum (ST) and its subregions, the caudate (CA) and the putamen (PU), were measured using the occipital cortex as the reference tissue. The reliability of the two measurements between test and retest, showed significant correlations for the ST, CA and PU, was demonstrated by calculating the intraclass correlation coefficient (ICC). Thus, (99m)Tc-TRODAT-1 SPECT might provide a reproducible and reliable tool in clinical management of young patients with DAT-related disorders.

Dopamine transporter density in the basal ganglia in obsessive-compulsive disorder, measured with [123I]IPT SPECT before and after treatment with serotonin reuptake inhibitors

It has been suggested that dopamine as well as serotonin are associated with the pathophysiology of obsessive-compulsive disorder (OCD). 5-Hydroxytryptophan inhibits dopamine release in healthy persons as well as in patients with OCD, and serotonin tonic inhibition affects dopamine function in basal ganglia, indicating a close relationship between serotonin and the dopamine system. Using iodine-123-labeled N-(3-iodopropen-2-yl)-2 beta-carbomethoxy-3beta-(4-chlorophenyl) tropane ([(123)I]IPT) single photon emission computed tomography (SPECT), we investigated the dopamine transporter (DAT) density in the basal ganglia of patients with OCD. The test consists of two measurements before and after treatment with serotonin reuptake inhibitors (SRIs). Ten patients with OCD before and after treatment with SRIs were included. We performed brain SPECT 2 h after intravenous administration of [(123)I]IPT using a dual-head SPECT camera (Vertex, ADAC, Calif., USA) and analyzed the SPECT data, reconstructed for the assessment of the specific/nonspecific DAT binding ratio in the basal ganglia. We then examined the correlation between the scores of OCD symptom changes, assessed with the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS), and DAT binding ratio. Patients with OCD after treatment with SRIs showed a significantly decreased DAT binding ratio in the right basal ganglia compared with baseline. A significant correlation was found between the total scores and compulsion score changes of the Y-BOCS and the changes of the DAT binding ratio of the right basal ganglia. These findings suggest that the dopaminergic neurotransmitter system of the basal ganglia could play an important role in the symptom improvement of OCD patients.

Applications of Clinical Dopamine Imaging

Recent technologic advances make it increasingly possible to image neurotransmitter systems in living human brain, The dopamine system has been most intensively studied owing to its involvement in several brain disorders such as Parkinson's disease and Huntington's disease, as well as psychiatric disorders such as schizophrenia, depression, and compulsive behavioral disorders of multiple types. A variety of aspects of dopamine receptor density, function, and dopaminergic terminal status can now be assessed using the minimally invasive neuroimaging techniques of positron emission tomography and single-photon emission computed tomography. Although these techniques are currently used most often in the context of research, clinical applications are rapidly emerging.

Reproducibility of [123I]PE2I binding to dopamine transporters with SPECT

PURPOSE

The iodinated cocaine derivative [(123)I]PE2I is a new selective ligand for in vivo studies of the dopamine transporter (DAT) with SPECT. Recently, a bolus/infusion (B/I) protocol for [(123)I]PE2I measurements of DAT density was established [Pinborg LH et al. J Nucl Med 2005;46:1119-271]. The aims of this study were, firstly, to evaluate the test-retest variability using the B/I protocol and, secondly, to evaluate the B/I approach in a new group of healthy subjects using two outcome parameters, BP(1) (C(ROI)/C(plasma)) and BP(2) (C(ROI)/C(REF)).

METHODS

Seven healthy subjects were subjected to [(123)I]PE2I SPECT scanning twice. For both studies, the two outcome parameters BP(1) and BP(2) were calculated based on two different methods for region of interest (ROI) delineation, namely manual delineation and probability map-based automatic delineation with MRI co-registration.

RESULTS

With manual delineation, striatal test-retest variability (absolute difference between first and second scan as a percentage of the mean) of BP(1) and BP(2) was 13.9% (range 1.8-35.7%) and 4.1% (range 0.5-9.7%) respectively. The probability map-based automatic delineation resulted in striatal test-retest variability of 17.2% (range 4.3-40.5%) and 5.2% (range 0.1-10.9%) respectively. The B/I approach provided stable brain activity from 120 to 180 min post injection in both high- and low-count regions with a mean % change/hour in striatal BP(2) of 10.6.

CONCLUSION

[(123)I]PE2I SPECT with the B/I approach yields a highly reproducible measure of striatal dopamine transporter binding. The appropriateness of a B/I protocol with a B/I ratio of 2.7 h (i.e. with a bolus worth 2.7 h of infusion) was confirmed in an independent sample of healthy subjects.

Correlation of dopamine transporter imaging with parkinsonian motor handicap: How close is it?

During the past decade, dopamine transporter (DAT) imaging with single photon emission computerized tomography (SPECT) or positron emission tomography (PET) has evolved as an objective in vivo marker of nigrostriatal neuron loss in Parkinson's disease (PD). We investigate the relationship between striatal DAT binding, measured with [(123)I]beta-CIT SPECT, and parkinsonian motor handicap in a sample of 59 PD patients with minimal to severe disability, and review published cross-sectional studies on the correlation between DAT imaging and motor symptoms in PD. Earlier studies as well as the present results show a good correlation between overall striatal DAT binding and global measures of disease severity such as the Hoehn and Yahr scale, the total score on the Unified Parkinson's Disease Rating Scale (UPDRS), and UPDRS activities of daily living, with a progressive decline of DAT binding with increasing disability. A number of studies found a significant inverse correlation of striatal DAT binding with UPDRS motor score. Bradykinesia, posture, gait, and other midline symptoms, such as speech and facial expression, compared with rigidity, seem to be more closely related to striatal DAT binding. By contrast, neither the severity of parkinsonian rest nor of action tremor is related to the degree of dopaminergic denervation as measured by DAT imaging. Motor symptoms in the clinically less affected body side show a closer correlation with striatal DAT binding than do symptoms occurring in the dominantly affected body side. The correlation of putamen and caudate DAT binding with parkinsonian motor handicap seems to be similar. Although there have been limited comparative studies applying [(18)F]fluorodopa PET and DAT imaging in the same group of PD patients, available data suggest that putamen [(18)F]fluorodopa uptake, when compared with striatal DAT binding, may be more closely related to parkinsonian motor handicap.