Low-energy High-resolution Collimator Research Articles

An energy-optimized collimator design for a CZT-based SPECT camera

In single photon emission computed tomography, it is a challenging task to maintain reasonable performance using only one specific collimator for radiotracers over a broad spectrum of diagnostic photon energies, since photon scatter and penetration in a collimator differ with the photon energy. Frequent collimator exchanges are inevitable in daily clinical SPECT imaging, which hinders throughput while subjecting the camera to operational errors and damage. Our objective is to design a collimator, which is independent of the photon energy, performs reasonably well for commonly used radiotracers with low- to medium-energy levels of gamma emissions. Using the Geant4 simulation toolkit, we simulated and evaluated a parallel-hole collimator mounted to a CZT detector. With the pixel-geometry-matching collimation, the pitch of the collimator hole was fixed to match the pixel size of the CZT detector throughout this work. Four variables, hole shape, hole length, hole radius/width and the source-to-collimator distance were carefully studied. Scatter and penetration of the collimator, sensitivity and spatial resolution of the system were assessed for four radionuclides including 57Co, 99mTc, 123I and 111In, with respect to the aforementioned four variables. An optimal collimator was then decided upon such that it maximized the total relative sensitivity (TRS) for the four considered radionuclides while other performance parameters, such as scatter, penetration and spatial resolution, were benchmarked to prevalent commercial scanners and collimators. Digital phantom studies were also performed to validate the system with the optimal square-hole collimator (23mm hole length, 1.28mm hole width, and 0.32mm septal thickness) in terms of contrast, contrast-to-noise ratio and recovery ratio. This study demonstrates promise of our proposed energy-optimized collimator to be used in a CZT-based gamma camera, with comparable or even better imaging performance versus commercial collimators such as low-energy high resolution (LEHR) and medium energy general purpose (MEGP) collimators.

The Effect of Parallel-hole Collimator Material on Image and Functional Parameters in SPECT Imaging: A SIMIND Monte Carlo Study.

The collimator in single-photon emission computed tomography (SPECT) is a critical component of the imaging system and plays an impressive role in the imaging quality. In this study, the effect of the collimator material on the radioisotopic image and its functional parameters was studied. The simulating medical imaging nuclear detectors (SIMIND) Monte Carlo program was used to simulate a Siemens E.CAM SPECT (Siemens Medical Solutions, Erlangen, Germany) system equipped with a low-energy high-resolution (LEHR) collimator. The simulation and experimental data from the SPECT imaging modality using 99mTc were obtained on a point source and Jaszczak phantom. Seventeen high atomic number materials were considered as LEHR collimator materials. In order to determine the effect of the collimator material on the image and functional parameters, the energy resolution, spatial resolution, contrast, and collimator characteristics parameters such as septal penetration and scatter-to-primary ratio were investigated. Energy spectra profiles, full width at half maximums (FWHMs) (mm) of the point spread function (PSF) curves, system sensitivity, and contrast of cold spheres of the Jaszczak phantom for the simulated and experiment systems have acceptability superimposed. The results of FWHM and energy resolution for the 17 collimators showed that the collimator made of 98% lead and 2% antimony could provide the best FWHM and energy resolution, 7.68 mm and 9.87%, respectively. The LEHR collimator with 98% lead and 2% antimony offers the best resolution and contrast when compared to other high atomic number metals and alloys.

Optimisation of quantitative lung SPECT applied to mild COPD: a software phantom simulation study.

BackgroundThe amount of inhomogeneities in a 99mTc Technegas single-photon emission computed tomography (SPECT) lung image, caused by reduced ventilation in lung regions affected by chronic obstructive pulmonary disease (COPD), is correlated to disease advancement. A quantitative analysis method, the CVT method, measuring these inhomogeneities was proposed in earlier work. To detect mild COPD, which is a difficult task, optimised parameter values are needed.MethodsIn this work, the CVT method was optimised with respect to the parameter values of acquisition, reconstruction and analysis. The ordered subset expectation maximisation (OSEM) algorithm was used for reconstructing the lung SPECT images. As a first step towards clinical application of the CVT method in detecting mild COPD, this study was based on simulated SPECT images of an advanced anthropomorphic lung software phantom including respiratory and cardiac motion, where the mild COPD lung had an overall ventilation reduction of 5%.ResultsThe best separation between healthy and mild COPD lung images as determined using the CVT measure of ventilation inhomogeneity and 125 MBq 99mTc was obtained using a low-energy high-resolution collimator (LEHR) and a power 6 Butterworth post-filter with a cutoff frequency of 0.6 to 0.7 cm−1. Sixty-four reconstruction updates and a small kernel size should be used when the whole lung is analysed, and for the reduced lung a greater number of updates and a larger kernel size are needed.ConclusionsA LEHR collimator and 125 99mTc MBq together with an optimal combination of cutoff frequency, number of updates and kernel size, gave the best result. Suboptimal selections of either cutoff frequency, number of updates and kernel size will reduce the imaging system’s ability to detect mild COPD in the lung phantom.

Characterization of parallel-hole collimator using Monte Carlo Simulation.

Objective:Accuracy of in vivo activity quantification improves after the correction of penetrated and scattered photons. However, accurate assessment is not possible with physical experiment. We have used Monte Carlo Simulation to accurately assess the contribution of penetrated and scattered photons in the photopeak window.Materials and Methods:Simulations were performed with Simulation of Imaging Nuclear Detectors Monte Carlo Code. The simulations were set up in such a way that it provides geometric, penetration, and scatter components after each simulation and writes binary images to a data file. These components were analyzed graphically using Microsoft Excel (Microsoft Corporation, USA). Each binary image was imported in software (ImageJ) and logarithmic transformation was applied for visual assessment of image quality, plotting profile across the center of the images and calculating full width at half maximum (FWHM) in horizontal and vertical directions.Results:The geometric, penetration, and scatter at 140 keV for low-energy general-purpose were 93.20%, 4.13%, 2.67% respectively. Similarly, geometric, penetration, and scatter at 140 keV for low-energy high-resolution (LEHR), medium-energy general-purpose (MEGP), and high-energy general-purpose (HEGP) collimator were (94.06%, 3.39%, 2.55%), (96.42%, 1.52%, 2.06%), and (96.70%, 1.45%, 1.85%), respectively. For MEGP collimator at 245 keV photon and for HEGP collimator at 364 keV were 89.10%, 7.08%, 3.82% and 67.78%, 18.63%, 13.59%, respectively.Conclusion:Low-energy general-purpose and LEHR collimator is best to image 140 keV photon. HEGP can be used for 245 keV and 364 keV; however, correction for penetration and scatter must be applied if one is interested to quantify the in vivo activity of energy 364 keV. Due to heavy penetration and scattering, 511 keV photons should not be imaged with HEGP collimator.

Comparative Study of Imaging Characteristics of I-125 Imaging Using the Siemens Inveon Scanner and Siemens Symbia TruePoint

Objective: Although Iodine-125 (125I) has been widely used for in vitro studies because of its relatively long half-life (60.1 days), 125I imaging is limited because of its low energy (27 - 35 keV), even in an animal-dedicated system. In this study, imaging characteristics of 125I were assessed using a small animal-dedicated imaging system and clinical scanner. Methods: Using the Siemens Inveon and Siemens Symbia TruePoint systems, imaging characteristics such as resolution, sensitivity, and image quality were compared. Mouse high resolution (MHR-0.5), mouse general purpose (MGP-1.0), and mouse high sensitivity (MHS-2.0) collimators were used for the Inveon scanner, and low energy high-resolution (LEHR) and low energy all-purpose (LEAP) collimators were used for the Symbia TruePoint. For animal imaging, 16.8 MBq of 125I was administered to BALB/c mice intravenously, and the planar image and single-photon emission computed tomography (SPECT) were obtained using both scanners. Results: The resolution of 125I for the Inveon scanner was 3.98 mm full width at half maximum (FWHM) at a 30-mm distance with the MHR-0.5 collimator, and the value of Symbia scanner was 8.72 mm FWHM at a 30-mm distance with the LEHR collimator. The sensitivity of 125I for the Inveon scanner was 21.87 cps/MBq, and the value for the clinical scanner was 30.55 cps/MBq. The planar images of mice were successfully obtained at the level of evaluating specific binding in both scanners. Conclusion: 125I small animal imaging can be achieved with a clinical scanner. This result may enhance the utilization of 125I small animal imaging using a clinical scanner.

An anthropomorphic phantom study of brain dopamine transporter SPECT images obtained using different SPECT/CT devices and collimators.

The aim of this study was to evaluate differences in dopamine transporter SPECT images among different SPECT/CT devices and to determine the most appropriate region of interest (ROI) for semiquantitative evaluation. An anthropomorphic striatal phantom was filled with (123)I solutions of different striatum-to-background radioactivity ratios. Data were acquired using 2 SPECT/CT devices equipped with low- to medium-energy general-purpose and low-energy high-resolution (LEHR) collimators. The SPECT images were reconstructed by filtered backprojection with both attenuation and scatter correction and then were analyzed using specific binding ratio (SBR). The most appropriate of 7 ROI types was determined, and we then compared the linearity and recovery of SBR among the different SPECT/CT devices and collimators. The linearity of SBR was excellent for all types of ROIs. The ROI contouring the striatum based on the CT images showed the best recovery of SBR using mean activity in the striatal ROI (SBRmean) (47.8%). For this ROI, the recovery of SBRmean for SPECT/CT with a LEHR collimator with thick septa and a long hole length was 61.6%-significantly higher than that of other devices. The ROI contouring the striatum based on CT images was considered appropriate for evaluating dopamine transporter SPECT/CT. Among the different SPECT/CT devices, an LEHR collimator designed for (123I)I imaging is recommended.

123I-MIBG Cardiac Imaging: Acquisition Protocols and Correction Methods for Quantitative Evaluation

Cardiac sympathetic imaging with 123I-MIBG offers unique insights into heart failure and neurodegenerative disease. Because of the diffuse nature of impairment, quantitative evaluation is indispensable, and the heart-to-mediastinum ratio is widely accepted as a valuable index. However, estimation of this index is highly dependent on acquisition protocol, especially collimator choice. A low-energy high-resolution collimator having thin septa is often used for 123I-MIBG imaging, and high-energy photons emitted from 123I readily penetrate the thin septa. The heart-to-mediastinum ratios are affected by accumulation in the lung and liver and are underestimated to various degrees. Medium-energy collimators having thick septa are less susceptible to septal penetration and are expected to offer a better indicator of cardiac sympathetic function. This review will provide an overview of the physics of 123I imaging and discuss acquisition protocols and correction methods for quantitative evaluation of cardiac 123I-MIBG imaging with special reference to the effect of septal penetration.

Multipinhole collimator with 20 apertures for a brain SPECT application.

Several new technologies for single photon emission computed tomography (SPECT) instrumentation with parallel-hole collimation have been proposed to improve detector sensitivity and signal collection efficiency. Benefits from improved signal efficiency include shorter acquisition times and lower dose requirements. In this paper, the authors show a possibility of over an order of magnitude enhancement in photon detection efficiency (from 7.6 × 10(-5) to 1.6 × 10(-3)) for dopamine transporter (DaT) imaging of the striatum over the conventional SPECT parallel-hole collimators by use of custom-designed 20 multipinhole (20-MPH) collimators with apertures of 0.75 cm diameter. Quantifying specific binding ratio (SBR) of (123)I-ioflupane or (123)I-iometopane's signal at the striatal region is a common brain imaging method to confirm the diagnosis of the Parkinson's disease. The authors performed imaging of a striatal phantom filled with aqueous solution of I-123 and compared camera recovery ratios of SBR acquired between low-energy high-resolution (LEHR) parallel-hole collimators and 20-MPH collimators. With only two-thirds of total acquisition time (20 min against 30 min), a comparable camera recovery ratio of SBR was achieved using 20-MPH collimators in comparison to that from the LEHR collimator study. Their systematic analyses showed that the 20-MPH collimator could be a promising alternative for the DaT SPECT imaging for brain over the traditional LEHR collimator, which could give both shorter scan time and improved diagnostic accuracy.

Evaluation of dead-time corrections for post-radionuclide-therapy 177Lu quantitative imaging with low-energy high-resolution collimators

Evaluation of dead-time corrections for post-radionuclide-therapy 177Lu quantitative imaging with low-energy high-resolution collimators

An improved method for estimating the heart-to-mediastinum ratio from cardiac sympathetic nerve imaging with low-energy high-resolution collimators

BackgroundSeptal penetration causes underestimation of the heart-to-mediastinum (H/M) ratio in cardiac 123I-metaiodobenzylguanidine (MIBG) imaging with a low-energy high-resolution (LEHR) collimator. We aimed to improve the method of estimating the H/M ratios using the LEHR collimator. Methods and Results4 hours after 123I-MIBG injection, 40 patients were imaged successively with the medium-energy (ME) and LEHR collimators using gamma cameras having 3/8-inch crystals. Severe underestimation of the H/M ratios was observed with the LEHR collimator when compared to the ME collimator. Narrowing the energy window width did not reduce the underestimation. Application of 123I-dual-window (IDW) correction using a narrow or wide subwindow reduced the underestimation substantially but not entirely. The H/M ratios estimated from the LEHR images with or without IDW correction were corrected based on their correlations with the ratios estimated from the ME images. This empiric correction removed systematic underestimation, and residual errors were reduced when the H/M ratios after IDW correction were converted using the empiric equation. The conversion equation was successfully applied to the correction of the H/M ratios determined in another 40 patients using a 5/8-inch crystal. ConclusionsIn estimating the H/M ratios using an LEHR collimator, empiric correction combined with IDW correction improves concordance with ME-based values in comparison with empiric correction alone.

Evaluation of the scattered radiation components produced in a gamma camera using Monte Carlo method

INTRODUCTION: This paper presents a simulation for evaluation of the scattered radiation components produced in a gamma camera PARK using Monte Carlo code SIMIND. It simulates a whole body study with MDP (Methylene Diphosphonate) radiopharmaceutical based on Zubal anthropomorphic phantom, with some spinal lesions. METHODS: The simulation was done by comparing 3 configurations for the detected photons. The corresponding energy spectra were obtained using Low Energy High Resolution collimator. The parameters related with the interactions and the fraction of events in the energy window, the simulated events of the spectrum and scatter events were calculated. RESULTS: The simulation confirmed that the images without influence of scattering events have a higher number of valid recorded events and it improved the statistical quality of them. A comparison among different collimators was made. The parameters and detector energy spectrum were calculated for each simulation configuration with these collimators using 99mTc. CONCLUSION: The simulation corroborated that LEHS collimator has higher sensitivity and HEHR collimator has lower sensitivity when they are used with low energy photons.

Simultaneous Tc-99m/I-123 dual-radionuclide myocardial perfusion/innervation imaging using Siemens IQ-SPECT with SMARTZOOM collimator

Simultaneous dual-radionuclide myocardial perfusion/innervation SPECT imaging can provide important information about the mismatch between scar tissue and denervated regions. The Siemens IQ-SPECT system developed for cardiac imaging uses a multifocal SMARTZOOM collimator to achieve a four-fold sensitivity for the cardiac region, compared to a typical parallel-hole low-energy high-resolution collimator, but without the data truncation that can result with conventional converging-beam collimators. The increased sensitivity allows shorter image acquisition times or reduced patient dose, making IQ-SPECT ideal for simultaneous dual-radionuclide SPECT, where reduced administrated activity is desirable in order to reduce patient radiation exposure. However, crosstalk is a major factor affecting the image quality in dual-radionuclide imaging. In this work we developed a model-based method that can estimate and compensate for the crosstalk in IQ-SPECT data. The crosstalk model takes into account interactions in the object and collimator-detector system. Scatter in the object was modeled using the effective source scatter estimation technique (ESSE), previously developed to model scatter with parallel-hole collimators. The geometric collimator-detector response was analytically modeled in the IQ-SPECT projector. The estimated crosstalk was then compensated for in an iterative reconstruction process. The new method was validated with data from both Monte Carlo simulations and physical phantom experiments. The results showed that the estimated crosstalk was in good agreement with simulated and measured results. After model-based compensation the images from simultaneous dual-radionuclide acquisitions were similar in quality to those from single-radionuclide acquisitions that did not have crosstalk contamination. The proposed model-based method can be used to improve simultaneous dual-radionuclide images acquired using IQ-SPECT. This work also demonstrates that ESSE scatter modeling can be applied to non-parallel-beam projection geometries.

Improved Detection of Sentinel Lymph Nodes in SPECT/CT Images Acquired Using a Low- to Medium-Energy General-Purpose Collimator

The use of the low-energy high-resolution (LEHR) collimator for lymphoscintigraphy causes the appearance of star-shaped artifacts at injection sites. The aim of this study was to confirm whether the lower resolution of the low- to medium-energy general-purpose (LMEGP) collimator is compensated by decrease in the degree of septal penetration and the reduction in star-shaped artifacts. A total of 106 female patients with breast cancer, diagnosed by biopsy, were enrolled in this study. Tc phytate (37 MBq, 1 mCi) was injected around the tumor, and planar and SPECT/CT images were obtained after 3 to 4 hours. When sentinel lymph nodes (SLNs) could not be identified from planar and SPECT/CT images by using the LEHR collimator, we repeated the study with the LMEGP collimator. Planar imaging performed using the LEHR and LEHR + LMEGP collimators positively identified SLNs in 96.2% (102/106) and 99.1% (105/106) of the patients, respectively. Using combination of planar and SPECT/CT imaging with the LEHR and LEHR + LMEGP collimators, SLNs were positively identified in 97.2% (103/106) and 100% (106/106) of the patients, respectively. The LMEGP collimator provided better results than the LEHR collimator because of the lower degree of septal penetration. The use of the LMEGP collimator improved SLN detection.

Technical Considerations of Phosphorous-32 Bremsstrahlung SPECT Imaging after Radioembolization of Hepatic Tumors: A Clinical Assessment with a Review of Imaging Parameters.

Background. Bremsstrahlung (BS) imaging during radioembolization (RE) confirms the deposition of radiotracer in hepatic/extrahepatic tumors. The aim of this study is to demonstrate 32P images and to optimize the imaging parameters. Materials and Methods. Thirty-nine patients with variable types of hepatic tumors, treated with the intra-arterial injection of 32P, were included. All patients underwent BS SPECT imaging 24–72 h after tracer administration, using low energy high resolution (LEHR) (18 patients) or medium energy general purpose (MEGP) (21 patients) collimators. A grading scale from 1 to 4 was used to express the compatibility of the 32P images with those obtained from CT/MRI. Results. Although the image quality obtained with the MEGP collimator was visually and quantitatively better than with the LEHR (76% concordance score versus 71%, resp.), there was no statistically significant difference between them. Conclusion. The MEGP collimator is the first choice for BS SPECT imaging. However, if the collimator change is time consuming (as in a busy center) or an MEGP collimator is not available, the LEHR collimator could be practical with acceptable images, especially in a SPECT study. In addition, BS imaging is a useful method to confirm the proper distribution of radiotherapeutic agents and has good correlation with anatomical findings.

Evaluation of dead-time corrections for post-radionuclide-therapy 177Lu quantitative imaging with low-energy high-resolution collimators

Dead-time (DT) effects rarely cause problems in diagnostic single-photon emission computed tomography (SPECT) studies; however, in post-radionuclide-therapy imaging, DT can be substantial. Therefore, corrections may be necessary if quantitative images are used in image-based dosimetry or for evaluation of therapy outcomes. This task is particularly challenging if low-energy collimators are used. Our goal was to design a simple method to determine the dead-time correction factor (DTCF) without the need for phantom experiments and complex calculations. Planar and SPECT/CT scans of a water phantom containing a 70 ml bottle filled with lutetium-177 (Lu) were acquired over 60 days. Two small Lu markers were used in all scans. The DTCF based on the ratio of observed to true count rates measured over the entire spectrum and using photopeak primary photons only was estimated for phantom (DT present) and marker (no DT) scans. In addition, variations in counts in SPECT projections (potentially caused by varying bremsstrahlung and scatter) were investigated. For count rates that were about two-fold higher than typically seen in post-therapy Lu scans, the maximum DTCF reached a level of about 17%. The DTCF values determined directly from the phantom experiments using the total energy spectrum and photopeak counts only were equal to 13 and 16%, respectively. They were closely matched by those from the proposed marker-based method, which uses only two energy windows and measures photopeak primary photons (15-17%). A simple, marker-based method allowing for determination of the DTCF in high-activity Lu imaging studies has been proposed and validated using phantom experiments.

Clinical Utility of Radiation Medicine 99mTc-Methylene Diphosphanate Bone Scintigraphy in the Early Diagnosis of Rheumatoid Arthritis.

The value of 99mTc-Methylene diphosphanate (99mTc-MDP) bone scan in predicting development of bony destruction, swelling, new bone erosions and skeletal deformities in small joints and bones was studied by visual evaluation of bone scans. 99m Tc-MDP was injected intravenously. 3 hours after the 99mTc-MDP injection, they have been underwent spot views of entire skeletons with planar scintigraphy in the anterior and posterior positions. All patients were examined under the Electronics Corporation of India Limited (ECIL) single head gamma camera imaging machine, equipped with a low-energy high-resolution parallel-hole collimator. In 9 patients with newly diagnosed rheumatoid arthritis a total of 60 patients of 99mTc-MDP bone scan were examined clinically, scintigraphically, and radiographically. The follow up period was 2 years. Seven patients found increased radiopharmaceutical increased in small joints. Onset of the rheumatoid disease was found in three out of seven patients. 2/9 patients, the joints which were eroded scintigraphically, was active at all the checkups. Erosions were detected earlier in foot joints than in finger joints. New erosions were especially prone to appear in joints with persisting and high scintigraphic activity. On the contrary, inactive joints by radionuclide scanning never eroded. Scintigraphic and clinical activity and radiographic erosion correlated significantly with each other. The sensitivity and specificity of visual scintigraphic assessment and the relative pixel activity method proved to be superior to the region of interest methods and clinical evaluation for prediction of bony erosions in patients of rheumatoid arthritis.

Design and performance evaluation of a 20-aperture multipinhole collimator for myocardial perfusion imaging applications

Single photon emission computed tomography (SPECT) myocardial perfusion imaging remains a critical tool in the diagnosis of coronary artery disease. However, after more than three decades of use, photon detection efficiency remains poor and unchanged. This is due to the continued reliance on parallel-hole collimators first introduced in 1964. These collimators possess poor geometric efficiency. Here we present the performance evaluation results of a newly designed multipinhole collimator with 20 pinhole apertures (PH20) for commercial SPECT systems. Computer simulations and numerical observer studies were used to assess the noise, bias and diagnostic imaging performance of a PH20 collimator in comparison with those of a low energy high resolution (LEHR) parallel-hole collimator. Ray-driven projector/backprojector pairs were used to model SPECT imaging acquisitions, including simulation of noiseless projection data and performing MLEM/OSEM image reconstructions. Poisson noise was added to noiseless projections for realistic projection data. Noise and bias performance were investigated for five mathematical cardiac and torso (MCAT) phantom anatomies imaged at two gantry orbit positions (19.5 and 25.0 cm). PH20 and LEHR images were reconstructed with 300 MLEM iterations and 30 OSEM iterations (ten subsets), respectively. Diagnostic imaging performance was assessed by a receiver operating characteristic (ROC) analysis performed on a single MCAT phantom; however, in this case PH20 images were reconstructed with 75 pixel-based OSEM iterations (four subsets). Four PH20 projection views from two positions of a dual-head camera acquisition and 60 LEHR projections were simulated for all studies. At uniformly-imposed resolution of 12.5 mm, significant improvements in SNR and diagnostic sensitivity (represented by the area under the ROC curve, or AUC) were realized when PH20 collimators are substituted for LEHR parallel-hole collimators. SNR improves by factors of 1.94–2.34 for the five patient anatomies and two orbital positions studied. For the ROC analysis the PH20 AUC is larger than the LEHR AUC with a p-value of 0.0067. Bias performance, however, decreases with the use of PH20 collimators. Systematic analyses showed PH20 collimators present improved diagnostic imaging performance over LEHR collimators, requiring only collimator exchange on existing SPECT cameras for their use.

Acquisition Protocols and Correction Methods for Estimation of the Heart-to-Mediastinum Ratio in 123I-Metaiodobenzylguanidine Cardiac Sympathetic Imaging

Septal penetration of high-energy photons affects quantitative results in imaging of (123)I-labeled tracers. We investigated acquisition protocols (collimator choice and energy window setting) and correction methods for estimating the heart-to-mediastinum (H/M) ratio in cardiac (123)I-metaiodobenzylguanidine (MIBG) imaging. Four hours after (123)I-MIBG injection, 40 patients successively underwent planar anterior chest imaging with the medium-energy (ME) (ME method) and low-energy high-resolution (LEHR) (LEHR method) collimators. A 20% energy window was used for both collimators. Another 40 patients were imaged successively with the ME collimator and a 20% window (ME method), the low-medium-energy (LME) collimator and a 20% window (LME20 method), and the LME collimator and a 15% window (LME15 method). The H/M ratios obtained by the LEHR, LME20, and LME15 methods were corrected using their correlations with the H/M ratio obtained by the ME method (empiric correction). The (123)I-dual-window (IDW) correction was also applied to remove the influence of high-energy photons. Without correction, severe underestimation of the H/M ratio was shown for the LEHR method using the ME method as a standard, and this underestimation increased with increasing H/M ratios. Underestimation substantially decreased using the LME20 method and further using the LME15 method. Empiric correction reduced the error in the H/M ratio by the LEHR method, but the error was still evident. After empiric correction, the H/M ratios with the LME collimator were comparable to those with the ME collimator. The IDW correction only partially reduced underestimation by the LEHR method and caused a small overestimation for the LME15 method. The use of an LME collimator appears to be acceptable for cardiac (123)I-MIBG imaging as an alternative to an ME collimator, and the application of a 15% energy window is recommended when an LME collimator is used. Empiric correction is also expected to improve exchangeability between H/M ratios calculated with ME and LME collimators. Neither the use of an LEHR collimator nor the use of IDW correction is recommended.

Effect of the NSAID Diclofenac on 99mTc-MAG3 and 99mTc-DTPA Renography

Renal function and disease are commonly evaluated by radionuclide studies. The choice of radiopharmaceutical agent for various studies is crucial for proper interpretation. (99m)Tc-mercaptoacetyltriglycine ((99m)Tc-MAG3) is excreted almost exclusively by the renal tubules, whereas (99m)Tc-diethylenetriamine pentaacetic acid ((99m)Tc-DTPA) is predominantly excreted by glomerular filtration. The present study compared the effect of the nonsteroidal antiinflammatory drug (NSAID) diclofenac, which is the most commonly used drug to relieve kidney pain, on the kinetic behavior of administered (99m)Tc-MAG3 and (99m)Tc-DTPA in experimental animals. Two groups of 12 New Zealand White rabbits ((99m)Tc-MAG3 and (99m)Tc-DTPA) were used for the renography. Each rabbit served as its own control. The animals were given 60 mL of saline intravenously 30 min before each renographic study. A baseline study (control) was done by injecting 48 MBq (1.3 mCi) of (99m)Tc-MAG3, and renography was performed. Two days later, a single intravenous dose of diclofenac (2 mg/kg) (treated animals) was given, and after 20 min, (99m)Tc-MAG3 renography was performed. This procedure was repeated for the (99m)Tc-DTPA group after administration of 96 MBq (2.6 mCi) of the tracer. Dynamic images (as 2-s frames for the first minute and 30-s frames for the next 30 min on a 64 × 64 matrix) were acquired using a γ-camera equipped with a low-energy high-resolution collimator interfaced with a computer. Regions of interest were drawn over the whole kidneys. Time-activity curves were generated from the region of interest. Time to peak activity (T(max)), time from peak to 50% activity (T(1/2)), and the uptake slope of each kidney were calculated from the renograms for control and treated rabbits. Administration of diclofenac shifted the experimental renogram curves to the right, compared with the control curves, indicating that there was a delayed renal uptake of the 2 tracers and clearance of the radioactivity. The calculated average values of T(max) for control and treated rabbits using (99m)Tc-MAG3 were 1.8 ± 0.5 and 6.35 ± 0.4 min, respectively, whereas those of (99m)Tc-DTPA were 3.4 ± 0.4 and 18.2 ± 2 min, respectively. The T1/2 for control and treated rabbits for (99m)Tc-MAG3 were 3.2 ± 0.07 and 6.6 ± 0.07 min, respectively, whereas those for (99m)Tc-DTPA were 10.1 ± 1 and 35 ± 4 min, respectively. The differences were statistically significant (P < 0.05). This study showed that diclofenac delayed both T(max) and T1/2. The NSAID-induced kinetic changes were considerably greater for (99m)Tc-DTPA than for (99m)Tc-MAG3. On the basis of these findings, it is suggested that (99m)Tc-MAG3 be used to perform renography for studies involving the use of NSAID administration to decrease any change that may occur due to the type of tracer and not to the condition of the kidney.

Performance of a high‐sensitivity dedicated cardiac SPECT scanner for striatal uptake quantification in the brain based on analysis of projection data

The authors have previously reported the advantages of high-sensitivity single-photon emission computed tomography (SPECT) systems for imaging structures located deep inside the brain. DaTscan (Isoflupane I-123) is a dopamine transporter (DaT) imaging agent that has shown potential for early detection of Parkinson disease (PD), as well as for monitoring progression of the disease. Realizing the full potential of DaTscan requires efficient estimation of striatal uptake from SPECT images. They have evaluated two SPECT systems, a conventional dual-head gamma camera with low-energy high-resolution collimators (conventional) and a dedicated high-sensitivity multidetector cardiac imaging system (dedicated) for imaging tasks related to PD. Cramer-Rao bounds (CRB) on precision of estimates of striatal and background activity concentrations were calculated from high-count, separate acquisitions of the compartments (right striata, left striata, background) of a striatal phantom. CRB on striatal and background activity concentration were calculated from essentially noise-free projection datasets, synthesized by scaling and summing the compartment projection datasets, for a range of total detected counts. They also calculated variances of estimates of specific-to-nonspecific binding ratios (BR) and asymmetry indices from these values using propagation of error analysis, as well as the precision of measuring changes in BR on the order of the average annual decline in early PD. Under typical clinical conditions, the conventional camera detected 2 M counts while the dedicated camera detected 12 M counts. Assuming a normal BR of 5, the standard deviation of BR estimates was 0.042 and 0.021 for the conventional and dedicated system, respectively. For an 8% decrease to BR = 4.6, the signal-to-noise ratio were 6.8 (conventional) and 13.3 (dedicated); for a 5% decrease, they were 4.2 (conventional) and 8.3 (dedicated). This implies that PD can be detected earlier with the dedicated system than with the conventional system; therefore, earlier identification of PD progression should be possible with the high-sensitivity dedicated SPECT camera.