High-resolution Fan-beam Collimators Research Articles

Design of a Multi-Pinhole Collimator for I-123 DaTscan Imaging on Dual-Headed SPECT Systems in Combination with a Fan-Beam Collimator.

For the 2011 FDA approved Parkinson's Disease (PD) SPECT imaging agent I-123 labeled DaTscan, the volume of interest (VOI) is the interior portion of the brain. However imaging of the occipital lobe is also required with PD for calculation of the striatal binding ratio (SBR), a parameter of significance in early diagnosis, differentiation of PD from other disorders with similar clinical presentations, and monitoring progression. Thus we propose the usage of a combination of a multi-pinhole (MPH) collimator on one head of the SPECT system and a fan-beam on the other. The MPH would be designed to provide high resolution and sensitivity for imaging of the interior portion of the brain. The fan-beam collimator would provide lower resolution but complete sampling of the brain addressing data sufficiency and allowing a volume-of-interest to be defined over the occipital lobe for calculation of SBR's. Herein we focus on the design of the MPH component of the combined system. Combined reconstruction will be addressed in a subsequent publication. An analysis of 46 clinical DaTscan studies was performed to provide information to define the VOI, and design of a MPH collimator to image this VOI. The system spatial resolution for the MPH was set to 4.7 mm, which is comparable to that of clinical PET systems, and significantly smaller than that of fan-beam collimators employed in SPECT. With this set, we compared system sensitivities for three aperture array designs, and selected the 3 × 3 array due to it being the highest of the three. The combined sensitivity of the apertures for it was similar to that of an ultra-high resolution fan-beam (LEUHRF) collimator, but smaller than that of a high-resolution fan-beam collimator (LEHRF). On the basis of these results we propose the further exploration of this design through simulations, and the development of combined MPH and fan-beam reconstruction.

Changes in Regional Cerebral Blood Flow After Repetitive Transcranial Magnetic Stimulation of the Left Dorsolateral Prefrontal Cortex in Treatment-Resistant Depression

Changes in Regional Cerebral Blood Flow After Repetitive Transcranial Magnetic Stimulation of the Left Dorsolateral Prefrontal Cortex in Treatment-Resistant Depression

Regional binding index of the radiolabeled selective 5-HT2A antagonist 123I-5-I-R91150 in the normal canine brain imaged with single photon emission computed tomography.

The pattern of the specific 5-HT2A (5-hydroxytryptamine 2A receptor) antagonist 123I-5-I-R91150 was measured in 10 healthy dogs without neurologic and behavior abnormalities. Eight cortical regions (left and right fronto-, temporo-, parieto-, and occipitocortical area), one global subcortical region (including the thalamic system) were compared with a reference region lacking receptors; that is, the cerebellum. The 123I labeled radioligand was injected intravenously 100-200 minutes before acquisition. Both transmission and emission data were obtained with a triple head gamma camera equipped with high-resolution fanbeam collimators. The emission data were corrected for scatter and attenuation. To delineate different cerebral regions more accurately, the regions of interest (ROI) defined in a former study on brain perfusion measured with 99mTc-ethyl cysteinate dimer (ECD) in the same dogs were used. The co-registration of the 99mTc-ECD and the 123I-5-I-R91150, obtained from each dog, was realized with the help of corresponding transmission maps. By normalizing each regional cerebral activity to the activity observed in the cerebellum, the regional radioactivity (binding index) could be relatively quantified. Highest brain uptake was noted in the frontocortical brain areas (right: 1.85, left: 1.89), followed by the temporocortical region (right: 1.58, left: 1.56). Least uptake was noted in the more caudal and middle brain regions [occipito- (right: 1.46, left: 1.41), parietocortical (right: 1.30, left: 1.26), and striatal region (1.19)]. No gender nor age influence was noted in this series. The 123I labeled serotonin-2A receptor ligand seems to have similar cortical binding in the normal canine brain, as shown in humans and other animal species. A frontocortical to occipitocortical (rostrocaudal) binding index gradient was identified within the dog, which has not been seen in imaging studies from humans and other animal species. The significance of these results will need further investigation. This normative data can be used to compare regional brain uptake of the 123I-radioligand to dogs with behavioral disorders related to the serotonergic system, in future studies.

Importance of the choice of the collimator for the detection ofsmall lesions in scintimammography: a phantom study

99mTc methoxyisobutylisonitrile planar scintimammography (SMM) is mostly performedusing low-energy high-resolution (LEHR) parallel collimators. We studiedwhether using a different collimator could improve the detection of small(<1.5 cm) lesions for which SMM sensitivity is poor. Thirty fourbreast phantom configurations were considered, either with hot spheressimulating lesions or without any spheres. For each configuration, fourplanar acquisitions were performed using LEHR, low-energy ultrahigh-resolution (LEUHR), high-resolution fan-beam (HRFB) and ultrahigh-resolution fan-beam (UHRFB) collimators. Images corresponding to the20% and 10% energy windows and to the Jaszczak subtraction werecalculated. A database including 156 borderline images was derived. Aftertraining, 10 observers scored the images for the presence of a sphere. Theperformances in sphere detection were studied using receiver operatingcharacteristic (ROC) analysis. For all types of image, the area under theROC curve was highest with the UHRFB collimator and lowest with either theLEUHR or the HRFB collimator. For the 10% energy window imagesconventionally used in SMM, the detection sensitivities averaged 91%,73%, 60% and 55% for the UHRFB, LEHR, HRFB and LEUHR collimatorsrespectively, for the same specificity of 64%. We conclude that detectionof small tumours in planar SMM might be significantly improved by using aUHRFB collimator instead of an LEHR collimator.

Investigation of the vertebrobasilar arterial system in vertigo by vestibulocochlear test, SPECT and angiography

Objective: Perfusion of the areas of cochleovestibular structures was investigated using Tc-99m HMPAO single photon emission computerized tomography (SPECT) in the young patients with vertigo presumed to have peripheral vestibular abnormalities and compared the results with cochleovestibular test results, and vertebrobasilar angiography findings. Methods and patients: The study was performed on 20 patients with vertigo and 17 control subjects who had performed vertebral arteriography due to another disease. The patients with vertigo presumed to be on peripheral vestibular disorder were included in the study. Systemic and otorhinolaryngological examination were carried out. Audiovestibular function was evaluated in all patients and control subjects. Brain SPECT was performed with a one-head rotating gamma camera system from 64 projections into a 64×64 matrix, using low energy and high-resolution fan beam collimators with a sampling time of 30 s. The images taken from cerebellum, temporal, parietal and occipital lobes which are supplied by a vertebrobasilar system were compared visually with the other side and asymmetry in the perfusion was searched. After cochleovestibular tests and laboratory had been completed, vertebral arteriography was performed bilaterally in all patients. Results of digital subtraction angiography (DSA) and the vestibulocochlear test were compared with images of SPECT. Data analysis was done with Yates χ 2 and percentages of sensitivity and specificity were calculated. Results: There was vestibular test and cochlear test abnormalities in eight and ten of the patients with vertigo, respectively. SPECT imaging showed hypoperfusion and decreased regional blood flow in 12 of the patients. There was statistically significant differences between the study and control groups in SPECT ( P<0.05). Five patients showed abnormal findings in DSA examinations. Conclusion: It is believed that SPECT may be helpful in the detection of vascular pathology in the patients with vertigo.

Evaluation of myocardial defect detection between parallel-hole and fan-beam SPECT using the Hotelling trace

The objective of this study was to implement the Hotelling trace (HT) to evaluate the potential increase in defect detection in myocardial SPECT using high-resolution fan-beam (HRF) versus parallel-hole (HRP) collimation and compare results to a previously reported human observer study (G.K. Gregoriou et al., ibid., vol. 42, p. 1267-75, 1995). Projection data from the 3D MCAT torso phantom were simulated including the effects of attenuation, collimator-detector response blurring and scatter. Poisson noise fluctuations were then simulated. The HRP and HRF collimators had the same spatial resolution at 20 cm. The total counts in the projection data sets were proportional to the detection efficiencies of the collimators and on the order of that found in clinical Tc-99m studies. In six left-ventricular defect locations, the HT found for HRF was superior to that for HRP collimation. For HRF collimation, the HT was calculated for reconstructed images using 64/spl times/64, 128/spl times/128 and 192/spl times/192 grid sizes. The results demonstrate substantial improvement in myocardial defect detection when the grid size was increased from 64/spl times/64 to 128/spl times/128 and slight improvement from 128/spl times/128 to 192/spl times/192. Also, the performance of the Hotelling observer in terms of the HT at the different grid sizes correlates at better than 0.95 to that found in human observers in a previously reported observer experiment and ROC study.

Long focal length, asymmetric fan beam collimation for transmission acquisition with a triple camera SPECT system

A system design for fast sequential SPECT/transmission CT on a three-headed SPECT camera is evaluated using Monte Carlo simulation. A long focal length (114 cm) asymmetric fan beam collimator is used with a stationary line source positioned at the focal line for transmission acquisition. The advantages of this system include: large field-of-view with 360 degree acquisition, high sensitivity to the transmission line source, high spatial resolution, easy transition between SPECT and transmission acquisition, and no moving line source. For transmission reconstruction an ML-EM algorithm was implemented for the asymmetric fan beam geometry. The results showed that with a 40 cm detector width, transmission reconstructions of a 38/spl times/26 cm elliptical body were effectively artifact-free. Reconstructions of a 46/spl times/31 cm body contained only minor truncation artifacts that did not substantially affect the attenuation compensated SPECT image. Contamination of the transmission data from radionuclide within the patient can be substantially reduced with this system by using a high resolution fan beam collimator. It is concluded that long focal length, asymmetric fan beam collimation, combined with iterative reconstruction, offers a promising approach for fast sequential SPECT/TCT on a three-headed SPECT camera.

Evaluation of the effect of reconstructed image pixel size on defect detectability in Tl-201 fan-beam SPECT by an observer performance study

The effect of reconstructed image pixel size in the fan-beam filtered backprojection method in myocardial defect detection was investigated using an observer performance study and receiver operating characteristics (ROC) analysis. A mathematical phantom of the human torso was used to model the anatomy and Thallium-201 (Tl-201) uptake in humans. Realistic projections from the phantom were simulated using a low-energy high resolution fan-beam collimator that incorporated the effects of photon attenuation, spatially varying detector response, scatter, and Poison noise. For a fan-beam collimator with a focal length of 55 cm and with a radius of rotation of 25 cm, the magnification at the center of rotation was two and the maximum magnification in the reconstructed region of interest was three. Myocardial defects were simulated as Gaussian-shaped decreases in Tl-201 uptake distribution. By changing the reconstructed image pixel size, five different classes of reconstructed images resulted, with projection bin width to reconstructed image pixel size (PBIP) ratios of 1, 2, 3, 4, and 5. The results from the observer study indicate that the reconstructed image pixel size has a significant effect on myocardial defect detection in reconstructed Tl-201 SPECT images. Moreover, the study indicated that in order to ensure maximum defect detectability the PBIP ratio should be at least as large as the maximum possible magnification within the reconstructed image array.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>