Resolution SPECT Research Articles

Positron Lymphography: Multimodal, High-Resolution, Dynamic Mapping and Resection of Lymph Nodes After Intradermal Injection of 18F-FDG

The lymphatic system plays a critical role in the maintenance of healthy tissues. Its function is an important indicator of the presence and extent of disease. In oncology, metastatic spread to local lymph nodes (LNs) is a strong predictor of poor outcome. Clinical methods for the visualization of LNs involve regional injection and tracking of (99m)Tc-sulfur colloid ((99m)Tc-SC) along with absorbent dyes. Intraoperatively, these techniques suffer from the requirement of administration of multiple contrast media ((99m)Tc-SC and isosulfan blue), unwieldy γ-probes, and a short effective surgical window for dyes. Preclinically, imaging of transport through the lymphatics is further hindered by the resolution of lymphoscintigraphy and SPECT. We investigated multimodal imaging in animal models using intradermal administration of (18)F-FDG for combined diagnostic and intraoperative use. PET visualizes LNs with high sensitivity and resolution and low background. Cerenkov radiation (CR) from (18)F-FDG was evaluated to optically guide surgical resection of LNs. Imaging of (18)F-FDG uptake used PET and sensitive luminescent imaging equipment (for CR). Dynamic PET was performed in both sexes and multiple strains (NCr Nude, C57BL/6, and Nu/Nu) of mice. Biodistribution confirmed the uptake of (18)F-FDG and was compared with that of (99m)Tc-SC. Verification of uptake and the ability to use (18)F-FDG CR to guide nodal removal were confirmed histologically. Intradermal injection of (18)F-FDG clearly revealed lymphatic vessels and LNs by PET. Dynamic imaging revealed rapid and sustained labeling of these structures. Biodistribution of the radiotracer confirmed the active transport of radioglucose in the lymphatics to the local LNs and over time into the general circulation. (18)F-FDG also enabled visualization of LNs through CR, even before surgically revealing the site, and guided LN resection. Intradermal (18)F-FDG can enhance the preclinical investigation of the lymphatics through dynamic, high-resolution, and quantitative tomographic imaging. Clinically, combined PET/Cerenkov imaging has significant potential as a single-dose, dual-modality tracer for diagnostics (PET/CT) and guided resection of LNs (Cerenkov optical).

Effects of voxel size and iterative reconstruction parameters on the spatial resolution of SPECT/CT

The purpose of this study was to evaluate the effects of voxel size and iterative reconstruction parameters on the radial and tangential resolution for 99mTc SPECT as a function of radial distance from isocenter. SPECT/CT scans of eight coplanar point sources of size smaller than 1 mm3 containing high concentration 99mTc solution were acquired on a SPECT/CT system with 5/8 inch NaI(Tl) detector and low‐energy, high‐resolution collimator. The tomographic projection images were acquired in step‐and‐shoot mode for 360 views over 360° with 250,000 counts per view, a zoom of 2.67, and an image matrix of 256×256 pixels that resulted in a 0.9×0.9×0.9 mm3 SPECT voxel size over 230 mm field‐of‐view. The projection images were also rebinned to image matrices of 128 × 128 and 64 × 64 to yield SPECT voxel sizes of 1.8×1.8×1.8 and 3.6×3.6×3.6 mm3, respectively. The SPECT/CT datasets were reconstructed using the vendor‐supplied iterative reconstruction software that incorporated collimator‐specific resolution recovery, CT‐based attenuation correction, and dual‐energy window‐based scatter correction using different combinations of iterations and subsets. SPECT spatial resolution was estimated as the full width at half maximum of the radial and tangential profiles through the center of each point source in reconstructed SPECT images. Both radial and tangential resolution improved with higher iterations and subsets, and with smaller voxel sizes. Both radial and tangential resolution also improved with radial distance further away from isocenter. The magnitude of variation decreased for smaller voxel sizes and for higher number of iterations and subsets. Tangential resolution was found not to be equal to the radial resolution, and the nature of the anisotropy depended on the distribution of the radionuclide and on the reconstruction parameters used. The tangential resolution converged faster than the radial resolution, with higher iterations and subsets. SPECT resolution was isotropic and independent of radial distance when reconstructed using filtered back‐projection. SPECT spatial resolution and therefore quantification of SPECT uptake via partial‐volume correction in clinical images were found to depend on the nature of activity distribution within the SPECT field‐of‐view and on the specific choice of iterative reconstruction parameters.PACS number: 87.57.uh, 87.57.cf, 87.87.nf

Improvement of image resolution of brain SPECT by use of the wide-angle offset acquisition method

Cerebral SPECT images require high spatial and contrast resolution for precise evaluation of the abnormal tracer distribution in the brain. A shorter data acquisition time is preferable so that artifacts due to patient movement are avoided. We tried to shorten data acquisition time applying larger sampling angle and offset acquisition method, in which half degree of the step angle was shifted in the opposite gamma camera of the dual-detector SPECT system. A simulation study was performed with a 3-dimensional mathematical phantom. The phantom studies were performed with a hot-rod phantom and a brain phantom. A clinical study with ⁹⁹(m)Tc-ECD SPECT was also performed on a patient who had a cerebral infarction. Reconstruction of images was done for the normal 6° and 12° onset and 12° offset. Data for the 12° offset were acquired by shifting of sampling angles of the opposite detector by half (6°) of the sampling angles of 12°. The MLEM algorithm was used for image reconstruction. Image qualities in the simulation study, the phantom studies, and the clinical study were compared for the 6° and 12° onset, and for the 12° offset by quantitative analysis with use of profile curves. Analysis of the profile curves revealed that the image quality of the 12° offset was better than that of the 12° onset and compared to that of the 6° onset in the simulation study, the phantom studies, and the clinical study. The present study indicates that wide-angle offset data acquisition improves the image resolution of brain SPECT compared to onset data acquisition with the same sampling time.

Investigation of the possibility of improving spatial resolution in SPECT with the combination of LaBr 3:Ce-based detector and 3D-OSEM reconstruction algorithms

This study investigates the potential of improving spatial resolution in SPECT imaging using a combination of LaBr 3:Ce detectors and 3D-OSEM image reconstruction algorithms. Potential spatial resolution improvement was assessed intrinsically and extrinsically using GATE Monte Carlo simulation. Significantly improved MTF of LaBr 3:Ce detectors suggests better resolution performance at all spatial frequencies. In comparison to conventional NaI(Tl) scintillators, a combination of the LaBr 3:Ce crystal and 3D-OSEM incorporating resolution recovery could significantly improve the extrinsic spatial resolution of SPECT images.

Arterial Wall Dosimetry for Non-Hodgkin Lymphoma Patients Treated with Radioimmunotherapy

Tumors in non-Hodgkin lymphoma (NHL) patients are often proximal to the major blood vessels in the abdomen or neck. In external-beam radiotherapy, these tumors present a challenge because imaging resolution prevents the beam from being targeted to the tumor lesion without also irradiating the artery wall. This problem has led to potentially life-threatening delayed toxicity. Because radioimmunotherapy has resulted in long-term survival of NHL patients, we investigated whether the absorbed dose (AD) to the artery wall in radioimmunotherapy of NHL is of potential concern for delayed toxicity. SPECT resolution is not sufficient to enable dosimetric analysis of anatomic features of the thickness of the aortic wall. Therefore, we present a model of aortic wall toxicity based on data from 4 patients treated with (131)I-tositumomab. Four NHL patients with periaortic tumors were administered pretherapeutic (131)I-tositumomab. Abdominal SPECT and whole-body planar images were obtained at 48, 72, and 144 h after tracer administration. Blood-pool activity concentrations were obtained from regions of interest drawn on the heart on the planar images. Tumor and blood activity concentrations, scaled to therapeutic administered activities-both standard and myeloablative-were input into a geometry and tracking model (GEANT, version 4) of the aorta. The simulated energy deposited in the arterial walls was collected and fitted, and the AD and biologic effective dose values to the aortic wall and tumors were obtained for standard therapeutic and hypothetical myeloablative administered activities. Arterial wall ADs from standard therapy were lower (0.6-3.7 Gy) than those typical from external-beam therapy, as were the tumor ADs (1.4-10.5 Gy). The ratios of tumor AD to arterial wall AD were greater for radioimmunotherapy by a factor of 1.9-4.0. For myeloablative therapy, artery wall ADs were in general less than those typical for external-beam therapy (9.4-11.4 Gy for 3 of 4 patients) but comparable for 1 patient (32.6 Gy). Blood vessel radiation dose can be estimated using the software package 3D-RD combined with GEANT modeling. The dosimetry analysis suggested that arterial wall toxicity is highly unlikely in standard dose radioimmunotherapy but should be considered a potential concern and limiting factor in myeloablative therapy.

Comparison of Different Types of Commercial Filtered Backprojection and Ordered-Subset Expectation Maximization SPECT Reconstruction Software

The aim of this study was to compare the performance of filtered backprojection (FBP) and ordered-subset expectation maximization (OSEM) reconstruction algorithms available in several types of commercial SPECT software. Numeric simulations of SPECT acquisitions of 2 phantoms were used: the National Electrical Manufacturers Association line phantom used for the assessment of SPECT resolution and a phantom with uniform, hot-rod, and cold-rod compartments. For FBP, no filtering and filtering of the projections with either a Butterworth filter (order 3 or 6) or a Hanning filter at various cutoff frequencies were considered. For OSEM, the number of subsets was 1, 4, 8, or 16, and the number of iterations was chosen to obtain a product number of iterations times the number of subsets equal to 16, 32, 48, or 64. The line phantom enabled us to obtain the reconstructed central, radial, and tangential full width at half maximum. The uniform compartment of the second phantom delivered the reconstructed mean pixel counts and SDs from which the coefficients of variation were calculated. Hot contrast and cold contrast were obtained from its rod compartments. For FBP, the full width at half maximum, mean pixel count, coefficient of variation, and contrast were almost software independent. The only exceptions were a smaller (by 0.5 mm) full width at half maximum for one of the software types, higher mean pixel counts for 2 of the software types, and better contrast for 2 of the software types under some filtering conditions. For OSEM, the full width at half maximum differed by 0.1-2.5 mm with the different types of software but was almost independent of the number of subsets or iterations. There was a marked dependence of the mean pixel count on the type of software used, and there was a moderate dependence of the coefficient of variation. Contrast was almost software independent. The mean pixel count varied greatly with the number of iterations for 2 of the software types, and the coefficient of variation increased with the number of iterations for all types of software. The mean pixel count, coefficient of variation, and contrast were almost constant for a fixed product number of iterations times the number of subsets, whatever the number of subsets or iterations. Most of the types of software were equivalent for FBP or OSEM reconstruction. However, a few differences were observed with some types of software and should be considered when they are used.

SU‐DD‐A4‐05: Effects of Pixel Size and OSEM Iteration Parameters On Tc‐99m SPECT Resolution

Purpose: To evaluate the effect of pixel size and OSEM iterative reconstruction parameters on radial (RR) and tangential (TR) Tc‐99m SPECT resolution versus distance from isocenter. Method and Materials: Ten high‐concentration Tc‐99m point sources of size <2mm3 were positioned coplanar 0–9 cm from isocenter in a cylindrical phantom with low‐concentration background. Emission scans were acquired on a SPECT/CT system (Symbia T6, Siemens Medical Solutions) with LEHR collimation in continuous (C) and step‐and‐shoot (SS) modes for 360 views over 360° at 0.9, 1.8 and 3.6 mm/pixel. Data were iteratively reconstructed with 3D‐OSEM incorporating resolution, CT‐based attenuation, and scatter modeling, for different combinations of iterations and subsets (IT_SUB): 1_18, 10_18, 20_18, 30_18, 30_36, 30_60, 30_90. SPECT resolution was estimated using a Gaussian fit of the radial and tangential profiles through each point source. Results: TR was consistently better than RR. Anisotropy was independent of pixel size and scan mode but decreased with IT times SUB (e.g., TR/RR=0.78 and 0.62 for 1_18 and 30_90 with 0.9 mm/pixel in SS). Both TR and RR improved linearly with distance away from isocenter. The center‐to‐periphery resolution differences decreased with IT times SUB (e.g., slopes of resolution versus radius were −0.74 and −0.45 for 20_18 and 30_36 with 0.9 mm/pixel in SS) and with smaller pixel sizes (e.g., slopes of resolution versus radius were −0.89, −0.82 and −0.74 for 3.6, 1.8 and 0.9 mm/pixel for 20_18 in SS). TR and RR improved as a power‐law with IT times SUB. The rate of improvement showed no obvious dependence on pixel size. TR and RR were similar between SS and C. Conclusion: Spatial resolution of SPECT images reconstructed iteratively exhibited power‐law dependence on IT times SUB, linear dependence on radial position, and exhibited TR/RR anisotropy — modeling of which are important for accurate SPECT quantification.

18F-DOPA-PET bei neuroendokrinen Tumoren (NET)

Der Nachweis von NET mittels planarer Szintigrafie oder Single-Photonen-Emissions-Tomografie (SPECT) ist gerade bei kleinen Befunden trotz spezifischer Radiopharmaka wie 111In-Octreotid oder 123I-MIBG durch die begrenzte Auflösung der Gammakamera limitiert. Die Positronenemissionstomografie (PET) hat gegenüber der konventionellen Bildgebung den Vorteil der höheren Ortsauflösung, die bei onkologischen Fragestellung am häufigsten eingesetzte 18F-Fluordesoxyglukose ist jedoch eher zum Nachweis von entdifferenzierten NET geeignet. Für den Einsatz der 18F-DOPA-PET bei neuroendokrinen Tumoren liegen wenige, aber in Hinblick auf die Sensitivität des Tumornachweises, viel versprechende Studien vor. Der Stellenwert von 18F-DOPA im Vergleich zu den 68Ga-markierten Somatostatinrezeptorliganden wird in Studien zu klären sein.

203Pb-Labeled α-Melanocyte–Stimulating Hormone Peptide as an Imaging Probe for Melanoma Detection

Peptide-targeted alpha-therapy with 7.4 MBq of (212)Pb-[1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid]-ReO-[Cys(3,4,10),d-Phe(7),Arg(11)]alpha-MSH(3-13) ((212)Pb-DOTA-Re(Arg(11))CCMSH) cured 45% of B16/F1 murine melanoma-bearing C57 mice in a 120-d study, highlighting its melanoma treatment potential. However, there is a need to develop an imaging surrogate for patient-specific dosimetry and to monitor the tumor response to (212)Pb-DOTA-Re(Arg(11))CCMSH therapy. The purpose of this study was to evaluate the potential of (203)Pb-DOTA-Re(Arg(11))CCMSH as a matched-pair SPECT agent for (212)Pb-DOTA-Re(Arg(11))CCMSH. DOTA-Re(Arg(11))CCMSH was labeled with (203)Pb in 0.5 M NH(4)OAc buffer at pH 5.4. The internalization and efflux of (203)Pb-DOTA-Re(Arg(11))CCMSH were determined in B16/F1 melanoma cells. The pharmacokinetics of (203)Pb-DOTA-Re(Arg(11))CCMSH was examined in B16/F1 melanoma-bearing C57 mice. A micro-SPECT/CT study was performed with (203)Pb-DOTA-Re(Arg(11))CCMSH in a B16/F1 melanoma-bearing C57 mouse at 2 h after injection. (203)Pb-DOTA-Re(Arg(11))CCMSH was easily prepared in NH(4)OAc buffer and completely separated from the excess nonradiolabeled peptide by reversed-phase high-performance liquid chromatography (RP-HPLC). (203)Pb-DOTA-Re(Arg(11))CCMSH displayed fast internalization and extended retention in B16/F1 cells. Approximately 73% of (203)Pb-DOTA-Re(Arg(11))CCMSH activity internalized after a 20-min incubation at 25 degrees C. After incubation of the cells in culture medium for 20 min, 78% of internalized activity remained in the cells. (203)Pb-DOTA-Re(Arg(11))CCMSH exhibited a biodistribution pattern similar to that of (212)Pb-DOTA-Re(Arg(11))CCMSH in B16/F1 melanoma-bearing mice. (203)Pb-DOTA-Re(Arg(11))CCMSH exhibited a peak tumor uptake of 12.00+/-3.20 percentage injected dose per gram (%ID/g) at 1 h after injection. The tumor uptake gradually decreased to 3.43+/-1.12 %ID/g at 48 h after injection. (203)Pb-DOTA-Re(Arg(11))CCMSH exhibited a peak tumor-to-kidney uptake ratio of 1.53 at 2 h after injection. The absorbed doses to the tumor and kidneys were 4.32 and 4.35 Gy, respectively, per 37 MBq. Whole-body clearance of (203)Pb-DOTA-Re(Arg(11))CCMSH was fast, with approximately 89% of the injected activity cleared through the urinary system by 2 h after injection. (203)Pb showed 1.6-mm SPECT resolution, which was comparable to (99m)Tc. Melanoma lesions were visualized through SPECT/CT images of (203)Pb-DOTA-Re(Arg(11))CCMSH at 2 h after injection. (203)Pb-DOTA-Re(Arg(11))CCMSH exhibited favorable pharmacokinetic and tumor imaging properties, highlighting its potential as a matched-pair SPECT agent for (212)Pb-DOTA-Re(Arg(11))CCMSH melanoma treatment.

A compact CT/SPECT system for small-object imaging

We report herein on a low-cost, high-performance dual imaging modality CT/SPECT system for small objects or animals. The system is realized from a commercial micro-focus X-ray tube, a Gd2O2S:Tb phosphor screen and a CCD camera. SPECT/planar imaging is obtained using a pinhole collimator with the same camera module as for X-ray/CT. Fusion of anatomic and functional images from the two modalities is easily accomplished by adjusting the magnification of the two modalities. Using an X-ray tube of 15 μm focal spot size, an image magnification of 1:1500, a field of view of 110 mm×110 mm, and adopting variable gamma detection geometry, the system may serve for numerous imaging applications and can be expanded into high-sensitivity (300 cpm/μCi), sub-millimeter (0.86 mm) SPECT resolution over a field of view of 20 mm in diameter.

Sentinel node SPECT-CT in breast cancer

The AIM of this study was to determine the additional value of SPECT/CT in sentinel node scintigraphy in breast cancer. Furthermore, it was our question to determine, whether the low-dose computed tomography component (LD-CT) can be used for axillary lymph node staging of clinically negative patients. 51 patients with invasive breast cancer <3 cm in diameter were included in our prospective investigation. SPECT/CT was performed on a dedicated scanner 30 minutes after subareolar injection of (99m)Tc-Nanocoll. Axillary staging with CT(LD) was performed using standard CT-criteria. SLN were allocated to an axillary level using SPECT alone and SPECT/CT. Additionally, the number of SLN on CT(LD) corresponding to the scintigraphic hot node was notified for each patient and compared to the number of SLN found with the gamma probe. In 45/51 evaluable patients SLN could be localised in level I in 43 patients and in level II in two patients (all positive) using SPECT-CT, whereas a clear allocation could not be obtained by SPECT alone. The number of SLN was discrepant between SPECT and CT(LD) in 13/45 patients. The number of SLN detected with the gamma probe (n = 68) not significantly differed from the number of SLN detected by CT(LD) (n = 65) but was significantly higher than with SPECT (n = 51). CT(LD) yielded a sensitivity of 35.7%, a specificity of 83.9%, a positive predictive value (PPT) of 50%, a negative predictive value (NPV) of 74.3% and a diagnostic accuracy of 68.9% for axillary staging with CT(LD). The additional information of SPECT/CT allows a more accurate characterization of the SN concerning size, depth and anatomical location. CT(LD) when performed during (99m)Tc-Nanocoll sentinel-SPECT/CT is not suitable for axillary staging in breast cancer patients with clinical negative axilla due to its low sensitivity and moderate specificity. Therefore, it does not influence the decision for SNB or ALND. The limited resolution of SPECT leads to an underestimation of the number of SLN compared to CT(LD) and the gamma probe.

Estudios SPECT-TAC con 67Ga de la enfermedad linfomatosa. Su aportación en la estadificación y seguimiento de la enfermedad

67Ga scintigraphy is an established method for the staging and follow-up of patients diagnosed of lymphomas. The aim of this study is to evaluate advantages of 67Ga SPECT-CT study over planar, SPECT and high resolution CT studies in lymphoma disease. One hundred and one 67Ga studies corresponding to 74 patients (46 men) were obtained, mean age 44 years. Thirty-eight patients (51 %) were diagnosed of Hodgkin's lymphoma and 36 were non-Hodgkin's lymphoma. All patients were evaluated with 67Ga and high-resolution CT studies. 67Ga studies were performed in a hybrid system, obtaining planar, SPECT and fused SPECT-CT imaging. Findings obtained from 67Ga studies were correlated with findings obtained from CT studies, both much in number of tumoral lesions and in their localization. Planar, SPECT, SPECT-CT and CT studies detected 123, 146, 155 and 132 lesions respectively. SPECT-CT and CT were concordant in 52 studies, while there was no concordance between SPECT-CT and CT in the remaining 49 studies, SPECT-CT detecting more lesions than CT in 28 of them. These findings changed the disease stage 18 times (18 % of whole studies). These results show better efficiency of 67Ga SPECT-CT compared to the other acquisition methods of 67Ga study and to CT for detection of tumoral lymphomatous lesions. 67Ga SPECT-CT study improves the diagnostic yield of the study with 67Ga in patients with lymphoma, providing better anatomical localization of tumoral lesions and detection of extraganglionar disease.

SU‐FF‐I‐76: Observed Inter‐Camera Variability of Clinically Relevant Performance Characteristics for SIEMENS Symbia® Gamma Cameras

Purpose: To evaluate the inter‐camera variability of clinically relevant performance characteristics for Symbia® gamma cameras (Siemens Medical Solutions, USA). Materials and Methods: Evaluation of the inter‐camera variability was based on measurements made with nine separate systems. Performance characteristics measurements were based on NEMA standards and AAPM Reports (#22 and #52). All of the measurements were performed using Tc‐99m (except Co‐57 for extrinsic resolution) and low‐energy high‐resolution collimation. Of the nine cameras, 4 have 3/8″ and 5 have 5/8″ crystals. Energy resolution, intrinsic and extrinsic spatial resolution, intrinsic integral and differential flood uniformity over the useful field‐of‐view, pixel size, deadtime, sensitivity, SPECT resolution, and SPECT integral uniformity were evaluated. The mean, standard deviation, and coefficient of variability (CV) of each metric were computed for each crystal thickness. Results: The mean (standard deviation) of the measured metrics for the 3/8″ and 5/8″ crystal systems, respectively, were as follows: energy resolution [FWHM‐%] of 9.5 (0.2) and 9.5 (0.3); intrinsic resolution [FWHM‐mm] of 3.46 (0.08) mm and 3.87 (0.09) mm; extrinsic resolution [FWHM‐mm] of 4.39 (0.09) mm and 4.70 (0.10) mm; integral uniformity [%] of 4.5 (0.4) and 4.7 (0.7); differential uniformity [%] of 2.6 (0.3) and 2.7 (0.2); pixel size [mm] of 0.601 (0.001) and 0.602 (0.001); maximum count rate [kcps] with 20% deadtime loss of 125 (18) and 130 (13); sensitivity [cpm/ Ci] of 203 (5) and 217 (8); SPECT resolution [FWHM‐mm] of 13.2 (0.1) and 13.4 (0.1); and SPECT integral uniformity [%] of 0.14 (0.02) and 0.13 (0.01). The mean and maximum CV were determined to be ∼6% and ∼17%, respectively, with the intrinsic uniformity, deadtime, and SPECT uniformity displaying the greatest CV amongst the different systems. Conclusions: All of the tested gamma cameras exhibited performance characteristics within specifications and the inter‐camera variability was observed to be low.

TH‐D‐330A‐01: Annual Gamma Camera QC: Techniques And Phantoms To Simplify The Implementation Of The NEMA NU‐1 Procedures For Tests Recommended By The ACR

The objective of this work is to present techniques to perform the NEMA tests that are suggested by the ACR for annual gamma camera QC. Since the recommendation contains nine tests, the goal is to devise simple and efficient procedures to reduce the required time without compromising the quality. Also included is a comparison of test equipment conforming to NEMA specifications to equipment made in‐house.The time to complete the annual QC is markedly reduced by the availability of specifically designed phantoms. They provide a reliable means to compare the cameras and to establish a performance baseline. For two tests, Multi Window Spatial Registration and SPECT Resolution with scatter, the NEMA prescribed equipment is compared with readily available devices. The comparison of the commercial MWSP device and the one produced in‐house showed that the average maximum difference of the center of mass for the three Ga‐67 peaks measured at various points across the crystal face is 0.35 mm vs. 0.33 mm for the commercial and the in‐house device, respectively. For the SPECT resolution using three capillary tubes filled with Tc‐99m, a NEMA phantom is compared to a modified Jaszczak phantom. The FWHM is 4.78 pxl vs. 4.79 pxl (radial) and 4.144 pxl vs. 4.167 pxl (azimuthal) for NEMA and Jaszczak phantom, respectively.Further topics include sensitivity, count rate performance, comparison of fit methods, and monitor/printer QC.

Database of normal human cerebral blood flow measured by SPECT: II. Quantification of I-123-IMP studies with ARG method and effects of partial volume correction

The limited spatial resolution of SPECT causes a partial volume effect (PVE) and can lead to the significant underestimation of regional tracer concentration in the small structures surrounded by a low tracer concentration, such as the cortical gray matter of an atrophied brain. The aim of the present study was to determine, using 123I-IMP and SPECT, normal CBF of elderly subjects with and without PVE correction (PVC), and to determine regional differences in the effect of PVC and their association with the regional tissue fraction of the brain. Quantitative CBF SPECT using 123I-IMP was performed in 33 healthy elderly subjects (18 males, 15 females, 54-74 years old) using the autoradiographic method. We corrected CBF for PVE using segmented MR images, and analyzed quantitative CBF and regional differences in the effect of PVC using tissue fractions of gray matter (GM) and white matter (WM) in regions of interest (ROIs) placed on the cortical and subcortical GM regions and deep WM regions. The mean CBF in GM-ROIs were 31.7 +/- 6.6 and 41.0 +/- 8.1 ml/100 g/min for males and females, and in WM-ROIs, 18.2 +/- 0.7 and 22.9 +/- 0.8 ml/100 g/min for males and females, respectively. The mean CBF in GM-ROIs after PVC were 50.9 +/- 12.8 and 65.8 +/- 16.1 ml/100 g/min for males and females, respectively. There were statistically significant differences in the effect of PVC among ROIs, but not between genders. The effect of PVC was small in the cerebellum and parahippocampal gyrus, and it was large in the superior frontal gyrus, superior parietal lobule and precentral gyrus. Quantitative CBF in GM recovered significantly, but did not reach values as high as those obtained by invasive methods or in the H2(15)O PET study that used PVC. There were significant regional differences in the effect of PVC, which were considered to result from regional differences in GM tissue fraction, which is more reduced in the frontoparietal regions in the atrophied brain of the elderly.

SPECT-TC con 123I-MIBG y sonda gamma portátil en la localización radioguiada de un feocromocitoma

We report a case of a 56-year-old male with high suspicion of an intraabdominal catecholamine-producer tumor. The patient underwent different diagnostic procedures including 123I-meta-iodobenzylguanidine (123I-MIBG) scintigraphy, with subsequent SPECT and low resolution CT for attenuation correction and anatomic and functional image fusion. After practicing a new 123I-MIBG scintigraphy the patient was taken to the operating room, where a hand-held gamma probe detector helped to localize the lesion.

The loss in brain SPECT resolution due to bed oscillation

The loss in brain SPECT resolution due to bed oscillation

Faisabilité de la tomoscintigraphie synchronisée cardiaque chez le rat avec une gamma caméra standard

Objective. – Demonstrate the feasibility of ECG gated SPECT in the rat using a standard gamma camera. Methods. – Pinhole magnifying properties enabled to improve SPECT resolution significantly, by taking physical and geometrical effects into account in the matrix projection operator. We described the projection of each object voxel in the projection plane using the pinhole collimator geometry for each projection condition. Then, deconvolution of the projections is automatically achieved by solving the linear system given by the projection equations with the ART algorithm. With a standard gamma-camera (ARGUS, Philips) and a pinhole collimator (1.1 mm diameter), we performed SPECT on a resolution phantom and gated SPECT on adult anaesthetized (isoflurane) rats (Sprague–Dawley), with ( n = 2) or without myocardial infarction ( n = 2). For myocardial perfusion 550 MBq of 99mTc-MIBI were employed and for ventriculography 550 MBq of 99mTc labelling red blood cells in vivo were used. We acquired 48 projections with a matrix size of 64 × 64 (16 phases/cycle) over 180° and 1 min for each projection. Results. – Phantom measurements show a clear increasing in tomographic spatial resolution (1.5 mm) and rat’s myocardial perfusion and ventricular function were obtained in normal and pathological conditions. Conclusion. – The reconstruction method demonstrates the feasibility of the technique and allows to discuss future improvements in small animal cardiac molecular imaging.

Quantitative accuracy of serotonergic neurotrans-mission imaging with high-resolution 123I SPECT

Summary Aim: Serotonin transporter (SERT) imaging can be used to study the role of regional abnormalities of neurotransmitter release in various mental disorders and to study the mechanism of action of therapeutic drugs or drugs’ abuse. We examine the quantitative accuracy and reproducibility that can be achieved with high-resolution SPECT of serotonergic neurotransmission. Method: Binding potential (BP) of 123I labeled tracer specific for midbrain SERT was assessed in 20 healthy persons. The effects of scatter, attenuation, partial volume, mis-registration and statistical noise were estimated using phantom and human studies. Results: Without any correction, BP was underestimated by 73%. The partial volume error was the major component in this underestimation whereas the most critical error for the reproducibility was misplacement of region of interest (ROI). Conclusion: The proper ROI registration, the use of the multiple head gamma camera with transmission based scatter correction introduce more relevant results. However, due to the small dimensions of the midbrain SERT structures and poor spatial resolution of SPECT, the improvement without the partial volume correction is not great enough to restore the estimate of BP to that of the true one.

Improving spatial resolution in SPECT with the combination of PSPMT based detector and iterative reconstruction algorithms

This paper investigates the possibility of developing a SPECT system that combines the high spatial resolution of position sensitive photomultiplier tubes (PSPMTs) with the excellent performance of iterative reconstruction algorithms. A small field of view (FOV) camera based on a PSPMT and a pixelized scintillation crystal made of CsI(Tl) have been used for the acquisition of the projections. With the use of maximum likelihood expectation maximization (ML-EM) and ordered subsets expectation maximization (OSEM) slices of the object are obtained while three-dimensional (3D) reconstruction of the object is carried out using a modified marching cubes (MMC) algorithm. The spatial resolution of tomographic images obtained with the system was 2–3 mm. The spatial resolution of a conventional system that uses filtered backprojection (FBP) for slices reconstruction was more than 9 mm.