Single Photon Emission Computed Tomography Activity Research Articles

Combined Brain-Perfusion SPECT and EEG Measurements Suggest Distinct Strategies for Speech Comprehension in CI Users With Higher and Lower Performance.

Cochlear implantation constitutes a successful therapy of inner ear deafness, with the majority of patients showing good outcomes. There is, however, still some unexplained variability in outcomes with a number of cochlear-implant (CI) users, showing major limitations in speech comprehension. The current study used a multimodal diagnostic approach combining single-photon emission computed tomography (SPECT) and electroencephalography (EEG) to examine the mechanisms underlying speech processing in postlingually deafened CI users (N = 21). In one session, the participants performed a speech discrimination task, during which a 96-channel EEG was recorded and the perfusions marker 99mTc-HMPAO was injected intravenously. The SPECT scan was acquired 1.5 h after injection to measure the cortical activity during the speech task. The second session included a SPECT scan after injection without stimulation at rest. Analysis of EEG and SPECT data showed N400 and P600 event-related potentials (ERPs) particularly evoked by semantic violations in the sentences, and enhanced perfusion in a temporo-frontal network during task compared to rest, involving the auditory cortex bilaterally and Broca’s area. Moreover, higher performance in testing for word recognition and verbal intelligence strongly correlated to the activation in this network during the speech task. However, comparing CI users with lower and higher speech intelligibility [median split with cutoff + 7.6 dB signal-to-noise ratio (SNR) in the Göttinger sentence test] revealed for CI users with higher performance additional activations of parietal and occipital regions and for those with lower performance stronger activation of superior frontal areas. Furthermore, SPECT activity was tightly coupled with EEG and cognitive abilities, as indicated by correlations between (1) cortical activation and the amplitudes in EEG, N400 (temporal and occipital areas)/P600 (parietal and occipital areas) and (2) between cortical activation in left-sided temporal and bilateral occipital/parietal areas and working memory capacity. These results suggest the recruitment of a temporo-frontal network in CI users during speech processing and a close connection between ERP effects and cortical activation in CI users. The observed differences in speech-evoked cortical activation patterns for CI users with higher and lower speech intelligibility suggest distinct processing strategies during speech rehabilitation with CI.

Radiomic detection of microscopic tumorous lesions in small animal liver SPECT imaging

BackgroundOur aim was to present a new data analysis technique for the early detection of tumorous lesions using single-photon emission computed tomography (SPECT) imaging. Beyond standardized uptake value (SUV) and standardized uptake concentration (SUC), the skewness and kurtosis parameters of whole liver activity distribution histograms were examined in SPECT images to reveal the presence of tumorous cells.MethodsFour groups of mice were used in our experiment: a healthy control group, a group of obese mice with high body mass index, and two tumorous groups (primary liver cancer group with chemically induced hepatocellular carcinoma (HCC); metastatic liver tumor group—xenograft of human melanoma (HM)). For the SPECT measurements, 99mTc-labeled aggregated albumin nanoparticles were administered intravenously 2 h before the liver SPECT scans (NanoSPECT/CT, Silver Upgrade, Mediso Ltd., Hungary) to image liver macrophages. Finally, SUV, SUC, skewness, and kurtosis of activity distributions were calculated from segmented whole liver volumes.ResultsHCC animals showed moderate 99mTc-albumin particle uptake with some visually identified cold spots indicating the presence of tumors. The visual detection of cold spots however was not a reliable marker of tumorous tissue in the metastatic group. The calculated SUV, SUC, and kurtosis parameters were not able to differentiate between the healthy and the tumorous groups. However, healthy and tumorous groups could be distinguished by comparing the skewness of the activity distribution.ConclusionBased on our results, 99mTc-albumin nanoparticle injection followed by liver SPECT activity distribution skewness calculation is a suitable image analysis tool. This makes possible to effectively and quantitatively investigate liver macrophage inhomogeneity and identify invisible but present liver cold spot lesions. Skewness as a direct image-derived parameter is able to show altered tissue function even before the visual manifestation of liver tumor foci. The skewness of activity distribution might be related to an inhomogeneous distribution of macrophage cells as a consequence of microscopic tumor burden in the liver.

Organ-specific SPECT activity calibration using 3D printed phantoms for molecular radiotherapy dosimetry.

BackgroundPatient-specific absorbed dose calculations for molecular radiotherapy require accurate activity quantification. This is commonly derived from Single-Photon Emission Computed Tomography (SPECT) imaging using a calibration factor relating detected counts to known activity in a phantom insert.MethodsA series of phantom inserts, based on the mathematical models underlying many clinical dosimetry calculations, have been produced using 3D printing techniques. SPECT/CT data for the phantom inserts has been used to calculate new organ-specific calibration factors for 99mTc and 177Lu. The measured calibration factors are compared to predicted values from calculations using a Gaussian kernel.ResultsMeasured SPECT calibration factors for 3D printed organs display a clear dependence on organ shape for 99mTc and 177Lu. The observed variation in calibration factor is reproduced using Gaussian kernel-based calculation over two orders of magnitude change in insert volume for 99mTc and 177Lu. These new organ-specific calibration factors show a 24, 11 and 8 % reduction in absorbed dose for the liver, spleen and kidneys, respectively.ConclusionsNon-spherical calibration factors from 3D printed phantom inserts can significantly improve the accuracy of whole organ activity quantification for molecular radiotherapy, providing a crucial step towards individualised activity quantification and patient-specific dosimetry. 3D printed inserts are found to provide a cost effective and efficient way for clinical centres to access more realistic phantom data.

The influence of triple energy window scatter correction on activity quantification for 1 7 7Lu molecular radiotherapy

Accurate activity quantification is the foundation for all methods of radiation dosimetry for molecular radiotherapy (MRT). The requirements for patient-specific dosimetry using single photon emission computed tomography (SPECT) are challenging, particularly with respect to scatter correction. In this paper data from phantom studies, combined with results from a fully validated Monte Carlo (MC) SPECT camera simulation, are used to investigate the influence of the triple energy window (TEW) scatter correction on SPECT activity quantification for Lu MRT.Results from phantom data show that; (1) activity quantification for the total counts in the SPECT field-of-view demonstrates a significant overestimation in total activity recovery when TEW scatter correction is applied at low activities (200 MBq). (2) Applying the TEW scatter correction to activity quantification within a volume-of-interest with no background activity provides minimal benefit. (3) In the case of activity distributions with background activity, an overestimation of recovered activity of up to 30% is observed when using the TEW scatter correction.Data from MC simulation were used to perform a full analysis of the composition of events in a clinically reconstructed volume of interest. This allowed, for the first time, the separation of the relative contributions of partial volume effects (PVE) and inaccuracies in TEW scatter compensation to the observed overestimation of activity recovery. It is shown, that even with perfect partial volume compensation, TEW scatter correction can overestimate activity recovery by up to 11%. MC data is used to demonstrate that even a localized and optimized isotope-specific TEW correction cannot reflect a patient specific activity distribution without prior knowledge of the complete activity distribution. This highlights the important role of MC simulation in SPECT activity quantification.

Compensatory Mechanism for Face Perception Suggested by a SPECT Activation Study

Background The bilateral temporo-occipital lobes are the usual site of pathology in patients with prosopagnosia. However, the mechanisms leading to this disorder are not fully understood. We investigated the neural mechanism of compensation for prosopagnosia in a patient with focal right posterior temporal lobe encephalitis without prosopagnosia. Methods A single-photon emission computed tomography (SPECT) scan was performed using a brain-dedicated 32-phototube SPECT scanner and technetium-99m hexamethyl-propylene amine oxime to measure regional cerebral blood flow (rCBF). A SPECT activation study was performed in each of two conditions: the familial faces retrieval task and a control task. Results The SPECT activation study revealed a significant increase in rCBF in the contralateral temporal lobe (from 72 during control conditions to 99 mL/100 g/min during the activation paradigm). Conclusions This finding suggests that the region contralateral to the brain lesion compensates for the function of face perception. Our result may explain the reason why prosopagnosia rarely occurs with single, well-circumscribed lesions. The activation pattern seen in this study may be helpful for understanding the neural mechanism of compensation for prosopagnosia.

Patient-specific tracer activity in MPI SPECT: A hands-on approach

Patient-specific tracer activity in MPI SPECT: A hands-on approach

The Effect of Milk, Water and Lemon Juice on Various Subdiaphragmatic Activity-Related Artifacts in Myocardial Perfusion Imaging.

Background:Subdiaphragmatic activity can produce subdiaphragmatic-related artifacts, which can degrade the quality of myocardial perfusion imaging (MPI).Objectives:We examined the impact of drinking milk, water, and lemon juice on different subdiaphragmatic-related artifacts by using 99mTc-sestamibi myocardial single-photon emission computed tomography (SPECT) in order to determine a feasible method for improving the image quality.Patients and Methods:A total of 179 patients (age 58 ± 9.6 years) were enrolled in this study. The patients were randomly divided into five groups. Ten minutes after injection of 740 MBq 99mTc-sestamibi in both pharmacologic stress and rest phases, the individuals in group 1 were given water and milk (125 mL of each); those in group 2 were given lemon juice (250 mL); group 3 was given milk (250 mL); and group 4 was given water (250 mL), whereas no intervention was performed in group 5. The study was double-blind for both subjects and data collectors. MPI was performed for all patients and image quality was controlled by 2 experienced nuclear physicians. Interfering activity was determined visually on reconstructed images and categorized as extracardiac normalization artifact, overlapping of activity, scattering of activity, and ramp filter artifact.Results:There were significant differences in terms of interfering activity among the five groups; group 3 (milk) had significantly lower interfering activity than other groups had, as defined by overlapping of activity (on both stress and rest images), ramp filter artifact (stress images), and scatter artifact (rest images) (P < 0.05). Furthermore, there was a significant difference in the incidence of good-quality images, with no interfering activity in group 3 in the resting state compared with the other groups in the study (P < 0.05).Conclusions:Drinking 250 mL of milk in either the stress phase or the rest phase of imaging diminishes interfering subdiaphragmatic-related artifacts, particularly overlapping of activity in MPI SPECT, resulting in better-quality images.

Nonlinear dual reconstruction of SPECT activity and attenuation images.

In single photon emission computed tomography (SPECT), accurate attenuation maps are needed to perform essential attenuation compensation for high quality radioactivity estimation. Formulating the SPECT activity and attenuation reconstruction tasks as coupled signal estimation and system parameter identification problems, where the activity distribution and the attenuation parameter are treated as random variables with known prior statistics, we present a nonlinear dual reconstruction scheme based on the unscented Kalman filtering (UKF) principles. In this effort, the dynamic changes of the organ radioactivity distribution are described through state space evolution equations, while the photon-counting SPECT projection data are measured through the observation equations. Activity distribution is then estimated with sub-optimal fixed attenuation parameters, followed by attenuation map reconstruction given these activity estimates. Such coupled estimation processes are iteratively repeated as necessary until convergence. The results obtained from Monte Carlo simulated data, physical phantom, and real SPECT scans demonstrate the improved performance of the proposed method both from visual inspection of the images and a quantitative evaluation, compared to the widely used EM-ML algorithms. The dual estimation framework has the potential to be useful for estimating the attenuation map from emission data only and thus benefit the radioactivity reconstruction.

Changes in SPECT Cerebral Blood Flow Following Japanese Style, Superficial Acupuncture at LI-4 and LI-11 in Healthy Volunteers

Japanese style, superficial acupuncture (SA) has been clinically evaluated for its therapeutic benefit, yet the neurophysiologic responses associated with SA remain unclear. This study was performed to measure changes in regional cerebral blood flow (rCBF) following SA at LI-4 and LI-11 in healthy volunteers using single photon emission computed tomography (SPECT). Changes in SPECT activity following Japanese style SA were compared to previous reports of SPECT changes following electroacupuncture (EA) at the same acupoints. Ten (10) healthy volunteers were enrolled for this study. A few days after the baseline brain SPECT, SA was performed at LI-4 and LI-11 for 15 minutes and a second brain perfusion image was acquired for each subject. We used SPM2 to analyze the changes in rCBF after SA through a paired t test. In addition, the differences of rCBF changes between SA and EA were compared using a two-sample t test. Cerebral blood perfusion significantly increased after SA in the left superior frontal gyrus, left middle cingulum, left insular, right medial orbital frontal gyrus, and right middle cingulum (paired t test, uncorrected p < 0.005), while no regions showed a significant decrease. The results comparing poststimulation images between SA and EA demonstrated that the perfusion in the right lingual, both thalamus, left middle temporal gyrus, left insula, and both cerebellum were significantly increased in SA compared with EA (false discovery rate [FDR] corrected p < 0.05). There were specific increase patterns of rCBF following SA at LI-4 and LI-11, which were similar to those following EA. However, there were significant differences in the decrease pattern of rCBF between SA and EA, which might be due to the difference of the strength of acupuncture stimulation between the two methods. These results may contribute to developing a better strategy to a select stimulation method in acupuncture therapy.

Imaging Evaluation in Otosclerosis: Single Photon Emission Computed Tomography and Computed Tomography

The aim of our study was to demonstrate the utility of diphosphonate bone single photon emission computed tomography (SPECT) in diagnosing otosclerosis and to correlate the findings from SPECT with age, gender, and sensorineural hearing loss. We also evaluated the ability of high-resolution computed tomography (HR-CT) in detecting otospongiotic and otosclerotic foci and correlated the HR-CT findings with the SPECT results. Seventy-three subjects with surgically confirmed otosclerosis underwent SPECT, and 45 of the 73 patients also underwent HR-CT of the petrous bones. In the patient sample examined in this study, SPECT demonstrated a sensitivity of 95.2% and a specificity of about 96.7%. By correlating the SPECT findings, we found an inverse relationship between bone radioactivity and age (i.e., greater disease activity in younger patients) and a direct relationship between bone radioactivity and the severity of sensorineural impairment in younger patients. In the 45 patients who also underwent HR-CT, the sensitivity of HR-CT (58%) was lower than that of SPECT, and the comparison between SPECT activity and the HR-CT findings (fenestral or retrofenestral type) demonstrated a statistically significant correlation between the morphological finding of bone demineralization (pericochlear foci) and a high uptake index. The use of SPECT seems to be highly effective in differentiating normal from pathological petrous bone. It also provides a quantitative evaluation of disease activity and shows a significant correlation with bone demineralization revealed by HR-CT.

Fully automated 3D basal ganglia activity measurement in dopamine transporter scintigraphy (Spectalyzer)

Semiquantitative evaluation of tracer uptake in basal ganglia is superior to visual assessment of images in dopamine transporter (DAT) scintigraphy especially in follow-up of the patients. Manual drawing of regions of interest (ROIs) in two-dimensional (2D) transaxial slices of the single photon emission computed tomography (SPECT) datasets leads to a large inter- and intra-reader variability, while being time consuming. Our aim was to investigate a technique that extracts 3D ROIs in a fully automated fashion and thus might provide reproducible user-independent results allowing better follow-up control and large-scale clinical studies. The highest activity of 123IFP-CIT is expected in the basal ganglia. The proposed method (Spectalyzer) uses the following steps to localize this maximum and extract the ROIs in 3D: (1) Dithers the SPECT volume to obtain a 3D volume with binary only. (2) Models the obtained point distributions as two multivariate Gaussian distributions and estimated their parameters using the expectation maximization algorithm. (3) Using the original SPECT activity values, thresholding is performed using a fixed percentage of maximum activity as a parameter to obtain the 3D ROIs. (4) A reference volume in the occipital region is automatically found based on the location of the two ROIs. (5) From the 3D ROIs, statistical information like mean and median activity and the volume is extracted, relative to the activity in the reference region. The resulting values are compared with values from manual 2D ROIs. Further validation is performed by means of an anthropomorphic striatal phantom. The method was evaluated on 12 SPECT volumes including anthropomorphic striatal phantoms. In all cases the two basal-ganglia were successfully localized and the 3D ROIs estimated, with perfect reproducibility. The obtained values for the mean activity showed the same trend with the values obtained manually and also with the results of the 2D semiautomatic software, but without the substantial inter- and intra-reader variations. The proposed method is successful in finding the 3D ROIs and performing the subsequent measurements automatically. It is proposed as an automatic reproducible approach for semiquantitative analysis of DAT scintigraphy.

Thalamic and limbic involvement in the mechanism of action of vagus nerve stimulation, a SPECT study

To unravel the mechanism of action of neurostimulation as a treatment for seizures, functional neuroimaging tools allow minimally invasive research in humans. We performed single-photon emission computed tomography (SPECT) in patients with epilepsy, treated with vagus nerve stimulation (VNS). Changes in regional cerebral blood flow (rCBF) at the time of initial stimulation as well as after chronic treatment were correlated with long-term clinical efficacy. In this pilot study, 27 patients (14 female and 13 male) who were treated with VNS at Ghent University Hospital for refractory epilepsy underwent a (99m)Tc-ECD (ethyl cystein dimer) SPECT activation study at the time the first stimulation train was administered. 12 patients underwent an additional (99m)Tc-ECD SPECT activation study 6 months later. Image acquisition was performed on a high-resolution triple-headed gamma camera. Significant rCBF changes were correlated with prospectively assessed clinical efficacy data. Significant rCBF changes were found in the thalamus, the hippocampus and the parahippocampal gyrus. Acute limbic hyper-perfusion and chronic thalamic hypo-perfusion correlate with positive clinical efficacy. Acute and chronic electrical stimulation of the vagus nerve induces rCBF changes that can be measured by SPECT on a group-basis. The thalamus and the limbic system are thought to play a key role in the mechanism of action of VNS.

Comparison Between 2D and 3D Dosimetry Protocols in 90Y-Ibritumomab Tiuxetan Radioimmunotherapy of Patients with Non-Hodgkin's Lymphoma

We compared the radiation-absorbed dose obtained from a two dimensional (2D) protocol, based on planar whole-body (WB) scans and fixed reference organ masses with dose estimates, using a 3D single-photon emission computed tomography (SPECT) imaging protocol and patient-specific organ masses. Six (6) patients with follicular non-Hodgkin's lymphoma underwent a computed tomography (CT) scan, 5 2D planar WB, and 5 SPECT scans between days 0 and 6 after the injection of (111)In-ibritumomab tiuxetan. The activity values in the liver, spleen, and kidneys were calculated from the 2D WB scans, and also from the 3D SPECT images reconstructed, using quantitative image processing. Absorbed doses after the administration of (90)Y-ibritumomab tiuxetan were calculated from the (111)In WB activity values combined with reference organ masses and also from the SPECT activity values and organ masses as estimated from the patient CT scan. To assess the quantitative accuracy of the WB and SPECT scans, an abdominal phantom was also studied. The differences between organ masses estimated from the patient CT and from the reference MIRD models were between -10% and +98%. Using the phantom, errors in organ and tumor activity estimates were between -86% and 10% for the WB protocol and between -43% and -6% for the SPECT protocol. Patient liver, spleen, and kidney activity values determined from SPECT were systematically less than those from the WB scans. Radiation-absorbed doses calculated with the 3D protocol were systematically lower than those calculated from the WB protocol (29%+/-26%, 73%+/-26%, and 33%+/-53% differences in the liver, spleen, and kidney, respectively), except in the kidneys of 2 patients and in the liver of 1 patient. Accounting for patient-specific organ mass and using SPECT activity quantification have both a great impact on estimated absorbed doses.

Blunted prefrontal perfusion in depressed patients performing the Tower of London task

Impairment of cognition is common in depression, and many tasks on which depressed patients are impaired are sensitive to frontal lobe dysfunction. Performance on the Tower of London (TOL) task, which includes setting up and maintaining multiple subgoals at the same time, has been shown to depend on intact prefrontal cortices. Single photon emission computed tomography (SPECT) with 99mTc-ethyl cysteinate dimer was used to compare cognitive activation in nine depressed patients and nine normal controls during performance of the TOL task. Planning times and accuracy were measured as performance parameters, and functional imaging data were analysed with statistical parametric mapping (SPM99) to determine significant voxel-wise differences in activation between the two groups. During activation, depressed patients were as accurate as controls but differed in that they spent more thinking time. These findings agree with the results of neuropsychological studies. Compared with the normal controls, depressed patients were characterized by a blunted perfusion response in the right middle frontal cortex [Brodmann area (BA) 6] and the left superior frontal gyrus (BA 9), and by increased perfusion in the right superior temporal gyrus (BA 21) and the insular cortex (BA 13). This study shows that a SPECT activation procedure using the TOL task under classical test conditions is feasible in depressed patients.

Application of a neuropsychological activation probe with SPECT: the 'Tower of London' task in healthy volunteers.

Human planning is a complex mental process that may be evaluated by the 'Tower of London' (TOL) task, which includes setting up and maintaining multiple subgoals at the same time. Although positron emission tomography and functional magnetic resonance imaging have provided reliable data on the recruitment of a neural network engaged in planning tasks, the experimental settings of these studies cannot be applied in clinical conditions. Hence, this study reports on the TOL task under classical neuropsychological test conditions using single photon emission computed tomography (SPECT) activation in 10 healthy subjects. Participants first performed a control task and then an activation task, i.e., the TOL planning task In the planning task, subjects were required to change, in the minimum number of moves possible, an initial arrangement of beads to match a goal arrangement. Subjects solved a set of eight TOL problems of increasing difficulty. A control task was designed such that it eliminates planning abilities, which is the process of interest. Planning times and accuracy were measured as performance parameters and functional imaging data were analysed with statistical parametric mapping (SPM99) to determine significant voxel-wise activations between the planning task and the control task. Both overall and for each difficulty level, measures of accuracy were within the normal range. Similar results were found for the overall thinking time and thinking times of each difficulty level. That is, performance of the healthy subjects during the TOL task replicated the typical pattern of results found with appropriate control samples in the literature. Also, activation of the right prefrontal cortex was consistent with other functional imaging results, thereby validating the use of the TOL task in a SPECT activation paradigm. Based on the present study it may be concluded that the close resemblance of the test conditions of the SPECT activation procedure with those of the TOL task in the investigation room constitutes a major advantage for future application of the SPECT activation procedure in clinical conditions.

Context-dependent reasoning in a cognitive bias task: Part II. SPECT activation study

A cognitive bias task (CBT) delineates two different cognitive selection mechanisms in the prefrontal cortex. To identify functional anatomy of context-dependent reasoning, we used technetium- 99mhexamethyl- propyleneamine oxime ( 99mTc HM-PAO) single photon emission computed tomography (SPECT) and statistical parametric mapping. Twelve right-handed men 20–24 years old were instructed to look at a target card and then select the choice card (among two) that they preferred (modified CBT; mCBT). They also selected a choice card 2 weeks later without prior presentation of a target card (control task). In both tasks, 99mTc HM-PAO was injected intravenously about 15 s after initiation of the mCBT or control task. Brain images were obtained using a gamma camera and reconstructed by a UNIX-based workstation. Statistical analysis compared all activated images to control images. Results associated with P values of less than 0.01 ( Z score >2.36) were depicted on T 1-weighted magnetic resonance images. All subjects preferred choices more similar to the target. SPECT activation occurred bilaterally in the dorsolateral prefrontal cortices and middle temporal gyri during performance of the CBT. Additionally, the left inferior prefrontal cortex and left fusiform gyrus showed significant activation compared with the control task. A neural network linking the temporal and prefrontal cortices prominently seen in the left hemisphere participates in context-dependent reasoning. Knowledge of such neural systems is essential for understanding prefrontal lobe function and dysfunction.

Assessment of resting perfusion with myocardial contrast echocardiography: Theoretical and practical considerations

Background The aim of this study was to perform a quantitative comparison between myocardial contrast echocardiography (MCE) and single-photon emission computed tomography (SPECT) in patients with prior myocardial infarction (MI). We also wanted to determine the optimal method for the intravenous administration of an ultrasound contrast agent in the clinical setting. Methods and Results Seventeen patients with resting perfusion defects in a single vascular territory on SPECT were studied. MCE was performed with intermittent harmonic imaging during continuous infusions of a second-generation ultrasound contrast agent (Sonovue, Bracco Diagnostics) in all 17 patients and after bolus injection in 8 of them. During continuous infusions, the video intensity (VI) ratio between the abnormal and normal myocardium at a pulsing interval (PI) of 8 cardiac cycles correlated well with the activity ratio between these segments on SPECT ( r = 0.73, P < .01). When information regarding microbubble velocity (MV) denoted as change in VI with increasing Pls was added, the correlation with SPECT activity ratio improved ( P < .05) significantly ( r = 0.87, P < .0001). Higher microbubble doses resulted in higher VI during continuous infusions with good myocardial opacification and no far-field attenuation until the highest dose was reached. With bolus injections, the VI ratio between the abnormal and normal myocardium at Pl of 1 and 5 cardiac cycles showed a modest correlation ( r = 0.46 and r = 0.48, respectively, P < .05) with activity ratios between these regions on SPECT. When a dose of microbubbles administered as a bolus produced adequate myocardial opacification, it invariably resulted in far-field attenuation. Conclusions In patients with prior MI, quantitative assessment of resting perfusion defects on MCE correlates well with regional activity on SPECT. Continuous infusions offer an advantage over bolus injections because they can provide an assessment of both relative VI and MV. Adjustment of the microbubble infusion rate produces adequate myocardial opacification without attenuation.

I-131 SPECT activity recovery coefficients with implicit or triple-energy-window scatter correction

We define a total-activity recovery coefficient, TARC, as the activity within a volume of interest applied to a set of images from single photon emission computed tomography (SPECT) divided by the true activity in that volume. Because of finite camera resolution, recovery-coefficient values are expected to be less than 1 for small objects. In this report, the TARC is measured as a function of volume, background activity and image-acquisition radius of rotation. A set of hollow spheres which vary in volume are filled with a solution of I-131 in water, and placed within a water-filled cylinder having an elliptical cross section. Tomographic-imaging measurements are carried out for two systems. The first utilizes an implicit scatter correction and the second triple-energy-window correction. Both systems employ a reconstructed-counts-to-activity conversion factor which varies with a measured background parameter and with the radius of rotation. Sphere and cylinder outlines are drawn on a CT scan and transferred to the SPECT scan via a 3-D image fusion. As expected, the inverse of the TARC increases as the sphere volume decreases. With implicit scatter correction, the TARC has no systematic dependence on either radius of rotation or background. With triple-energy-window scatter correction, there is an increase in 1/TARC when the radius of rotation is increased by 5 cm. This increase ranges from 9% to 25% depending on volume. For all conditions, 1/TARC is fit to a power-law equation as a function of sphere volume. The use of the resultant equations to correct a measured activity for a small volume is outlined. Accuracy of the present relationships for target shapes which are not spherical is not addressed.

Autoradiographic and SPECT imaging of cerebral opioid receptors with an iodine-123 labeled analogue of diprenorphine.

The feasibility of imaging cerebral opioid receptors by single photon emission computed tomography (SPECT) has been established in baboon using a novel analog of diprenorphine (DPN) radiolabeled with iodine-123. The radioligand, [123I]-O-IA-DPN (C6-O-[123I]iodoallyl-DPN), was prepared in good yield (80%) with high radiochemical purity (>97%) and high specific radioactivity (>2,400 mCi/micromol). In ex vivo autoradiographic studies, with and without naltrexone blockade, [123I]-O-IA-DPN specifically labeled opioid receptors throughout the mouse brain. Nonmetabolized radioligand accounted for >90% of the signal observed in extracts of whole mouse brain. SPECT imaging trials showed that [123I]-O-IA-DPN selectively localized in regions of baboon brain known to have high densities of opioid receptors, such as striatum, thalamus, and temporal cortex. A much lower level of radioligand uptake and retention was noted for cerebellum, a region with few opioid binding sites. Pretreatment with naltrexone (6.5 pmol/kg) blocked [123I]-O-IA-DPN binding in all brain regions. Using naltrexone blockade to define the nonspecific component for a given region of interest, total to nonspecific binding ratios increased linearly (r > or = 0.98) over the SPECT study with maximal values for striatum (9.8), thalamus (7.1), and temporal cortex (6.9) reached at the last time point investigated (3.5 h). Specific binding for these regions, assessed as the difference between regional SPECT activity for the control and blocked states, proved irreversible over the observation period. By the end of the time course, specific [123I]-O-IA-DPN binding was >85% of total radioactivity in regions rich in opioid receptors and 62% of total radioactivity in cerebellum. The aggregate data are consistent with visualization of multiple opioid receptor types. Thus, [123I]-O-IA-DPN should prove useful for SPECT studies within the constraints imposed by a lack of innate selectivity for a single type of brain opioid receptor.

Evaluation of the factors affecting the accuracy and precision of a technique for quantification of volume and activity in SPECT.

The use of the technique of maximization of interclass variance to determine the threshold level defining the volume of an object in single photon emission computed tomography (SPECT) and hence its activity has been evaluated in a variety of conditions. The influence of varying activity on volume assessment and varying volume on activity assessment were shown to be negligible. The effect of object shape for the range of shapes likely to be found in the body was also small. Non-uniformity of activity in the object caused an underestimation of volume and to a lesser extent its activity. However, with activity varying by 100% within the volume, volume was only underestimated by 10% and activity by 3%. The presence of activity surrounding the object caused an overestimation of volume which increased linearly with the relative level of surrounding activity. The object to surrounding activity concentration ratio could be estimated and therefore its effect corrected. The influence of nearby objects and methods of dealing with their effect on the technique are described. Activity concentrations in objects with uniform distribution assessed using total activity divided by total volume were shown to be more accurate than assessments from maximum voxel count rate for objects with a volume below 150 ml.