High-resolution Collimator Research Articles

A study on sensitivity correction factor of gamma camera in whole body bone image

The aim of this study was to calculate a reasonable correction factor that could be corrected when the sensitivity of each gamma camera is measured and a whole body bone scan is performed as a follow-up examination. Seven pieces of equipment were used to analyse the sensitivity measurements of each gamma camera based on the source sensitivity measurement method recommended by the IAEA. These were BRIGHTVIEW, PRECEDENCE, ECAM, ECAM signature, ECAM Plus, SYMBIA T2 and INFINIA. The 99mTc line source for the sensitivity measurement was generated in 4–7 kcps, which are the common values in a whole body bone scan. All the cameras were equipped with a low-energy and high-resolution parallel multi-hole collimator and set at a window width and photo peak of 15% and 140 keV, respectively. After placing the 99mTc source as closely as possible to the collimator, the count was measured for 60 and 120 seconds to calculate correction factor. To determine if the correction factor calculated using the 99mTc line source could be applied to a whole body bone scan of a real patient, a whole body bone scan was performed on 27 patients before applying the correction factor for comparative analysis. According to the experimental results using the 99mTc line source, the gamma camera sensitivity was the highest for ECAM plus, followed in order by the gamma cameras, ECAM signature, SYMBIA T2, ECAM, BRIGHTVIEW, INFINIA and PRECEDENCE. When the results were used to calculate the correction factor based on the ECAM gamma camera, which had a medium-degree of sensitivity, the respective correction factors were 1·07, 1·05, 1·03, 1·00, 0·90, 0·83 and 0·72. The correction factors calculated based on the experiment using a 99mTc line source were similar to those calculated based on the whole body bone scan. Clinical application of correction factor for measured sensitivity enables estimation of factor correction depending on difference in equipment when image is read, which improves accuracy and reliability of examination, and is expected to be used especially for continuous follow-up examination.

WE-G-141-08: Simultaneous Reduction of Radiation Dose and Scatters for CBCT by Using Collimators

Purpose: On-board CBCT has been widely available in radiotherapy clinic for target localization. However, the extra radiation dose is always a concern for its frequent use. Additionally, the relatively large scatters in CBCT often impair the image quality. By using collimators/grids, some of the X-rays are stopped from reaching the patient and the detectors, hence both the scatters and the patient dose are simultaneously reduced. We show in this work that the data can still be reconstructed without any noticeable artifacts. We further investigate the relationship between the CBCT image quality and the amount of beams being blocked by collimators. Methods: A CBCT system with collimators was simulated following the typical geometry used in clinic. Different collimator designs were tested by varying the size and the number of the collimator holes, and at the same time, the ratio between transmitted beams to blocked beams was varied from 10 to 1/10, resulting in hundreds of different simulation scenarios. The simulated projections for lung and pelvis phantoms were reconstructed using the total variation technique. The image quality was examined by root mean square errors (RMSEs) and compared with the conventional CBCT image. Results: The CBCT image quality increases as the amount of beams passing through the collimators increases, and decreases as the size of the collimator holes increases while keeping the beam transmission rate constant. With ultra-high resolution collimators, the RMSEs were comparable to the conventional CBCT image until the beam transmission rate is reduced below 20%. Conclusion: Both the scatters and radiation dose can be dramatically reduced for CBCT by using collimators, while the image quality remains similar to the conventional CBCT. With high resolution collimators, the patient dose reduction can easily reach 1/4 of the conventional CBCT.

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.

A four-pixel matched collimator for high-sensitivity SPECT imaging

We propose a wide aperture parallel-hole collimator that we call a 4-pixel matched collimator (4-PMC) for high-sensitivity SPECT imaging. The hole size of the 4-PMC is matched to four detector pixels; that is, there are four (2 × 2) pixels per collimator hole. By contrast, a 1-pixel matched collimator (1-PMC) is defined as a collimator whose hole size is matched to one detector pixel. We evaluated four types of collimator (high-resolution collimator versions and high-sensitivity collimator versions of both 4-PMC and 1-PMC) by simulation. SPECT images of a cylindrical phantom with cold spots in the noise-free condition demonstrated that the 4-PMC provided a higher-contrast image than the 1-PMC for the same collimator version. In addition, SPECT images at the noise level corresponding to a human cerebral blood flow study suggested that the high-sensitivity version of the 4-PMC provided the highest contrast image among the four collimator types. In conclusion, the high-sensitivity SPECT system using the 4-PMC can improve the trade-off between spatial resolution and sensitivity and will consequently provide improved image contrast for clinical studies of the human brain compared with the SPECT system using the 1-PMC.

Evaluation of a matched filter resolution recovery reconstruction algorithm for SPECT-CT imaging

The aim of our study was to assess improvements in spatial resolution and noise control from the application of the Astonish resolution recovery algorithm for single photon emission computed tomography imaging. Secondary aims were to compare acquisitions made with low-energy general purpose collimators with those obtained using low-energy high-resolution collimators in this context and evaluate the potential of a finer matrix to improve image quality further. A Tc-filled Jaszczak phantom with hot spheres was used to assess contrast and noise. A National Electrical Manufacturers Association triple line source single photon emission computed tomography resolution phantom was used to measure spatial resolution. Acquisitions were made using both low-energy high-resolution and low-energy general purpose collimators. Compared with standard ordered subsets expectation maximization reconstructions, the resolution recovery algorithm resulted in a higher spatial resolution (8 vs. 14 mm full-width at half-maximum) leading to reduced partial volume effects in the smaller Jaszczak spheres. Higher image contrast was achieved alongside lower levels of noise. An edge enhancement artefact was observed in the resolution recovery corrected images. An overestimate of the target-to-background activity was also observed for the larger spheres. The use of such an algorithm results in images characterized by increased spatial resolution and reduced noise. However, small sources of the order of 2-3 cm can be significantly overenhanced.

Quantification of myocardial area at risk in the absence of collateral flow: The validation of angiographic scores by myocardial perfusion single-photon emission computed tomography

ObjectivesOur study aimed to compare the area at risk (AAR) determined by single-photon emission computed tomography (SPECT) with the Bypass Angioplasty Revascularization Investigation (BARI) and modified Alberta Provincial Project for Outcome Assessment in Coronary Heart Disease (APPROACH) angiographic scores in the setting of patients undergoing coronary angioplasty for either unstable angina or an STEMI. BackgroundRadionuclide myocardial perfusion imaging prior to reperfusion has classically been the most widely practised technique for assessing the AAR and has been successfully used to compare the efficacy of various reperfusion strategies in patients with an ST-segment elevation myocardial infarction (STEMI). The BARI and modified APPROACH scores are angiographic methods widely used to provide a rapid estimation of the AAR; however, they have not been directly validated with myocardial perfusion single-photon emission computed tomography (SPECT). MethodsFifty-five patients with no previous myocardial infarction who underwent coronary angioplasty for single-vessel disease (unstable angina: n = 25 or an STEMI: n = 30) with no evidence of collaterals (Rentrop Collateral Score <2) were included in a prospective study. In STEMI patients, the 99mTc-tetrofosmin was injected prior to opening of the occluded vessel and, in patients with unstable angina after 10-15 seconds of balloon inflation. Acquisition was performed with a dual-head gammacamera with a low-energy and high-resolution collimator. A total of 60 projections were acquired using a non-circular orbit. No attenuation or scatter correction was used. Maximal contours of hypoperfusion regions corresponding to each coronary artery occlusion were delineated over a polar map of 17 segments and compared with the estimated AAR determined by two experienced interventional cardiologists using both angiographic scores. ResultsMean AAR percentage in SPECT was 35.0 (10.0%-56.0%). A high correlation was found between BARI and APPROACH scores (r= 0.9, P< .001). Furthermore, a high correlation was also observed between BARI versus SPECT and APPROACH versus SPECT to estimate the AAR (r= 0.9, P< .001 and r= 0.8, P< .001, respectively). Better correlations were observed when the left anterior descending artery (LAD) was revascularized (r= 0.8, P< 0.001 with BARI; r= 0.8, P= .001 with APPROACH) compared to other territories (r= 0.8, P= .001 with BARI; r= 0.7, P= .001 with APPROACH). Also, better correlations were observed in patients who underwent an elective rather than a primary percutaneous revascularization procedure. ConclusionsIn the absence of collateral flow, BARI and APPROACH scores constitute valid methods for AAR estimation in current clinical practice, with more accurate results when used for the LAD territory; both are useful not only in STEMI patients but also in patients with unstable angina.

Performance evaluation of small-animal multipinhole μSPECT scanners for mouse imaging

We compared the performance of three commercial small-animal μSPECT scanners equipped with multipinhole general purpose (GP) and multipinhole high-resolution (HR) collimators designed for imaging mice. Spatial resolution, image uniformity, point source sensitivity and contrast recovery were determined for the U-SPECT-II (MILabs), the NanoSPECT-NSO (BioScan) and the X-SPECT (GE) scanners. The pinhole diameters of the HR collimator were 0.35 mm, 0.6 mm and 0.5 mm for these three systems respectively. A pinhole diameter of 1 mm was used for the GP collimator. To cover a broad field of imaging applications three isotopes were used with various photon energies: (99m)Tc (140 keV), (111)In (171 and 245 keV) and (125)I (27 keV). Spatial resolution and reconstructed image uniformity were evaluated in both HR and a GP mode with hot rod phantoms, line sources and a uniform phantom. Point source sensitivity and contrast recovery measures were additionally obtained in the GP mode with a novel contrast recovery phantom developed in-house containing hot and cold submillimetre capillaries on a warm background. In hot rod phantom images, capillaries as small as 0.4 mm with the U-SPECT-II, 0.75 mm with the X-SPECT and 0.6 mm with the NanoSPECT-NSO could be resolved with the HR collimators for (99m)Tc. The NanoSPECT-NSO achieved this resolution in a smaller field-of-view (FOV) and line source measurements showed that this device had a lower axial than transaxial resolution. For all systems, the degradation in image resolution was only minor when acquiring the more challenging isotopes (111)In and (125)I. The point source sensitivity with (99m)Tc and GP collimators was 3,984 cps/MBq for the U-SPECT-II, 620 cps/MBq for the X-SPECT and 751 cps/MBq for the NanoSPECT-NSO. The effects of volume sensitivity over a larger object were evaluated by measuring the contrast recovery phantom in a realistic FOV and acquisition time. For 1.5-mm rods at a noise level of 8 %, the contrast recovery coefficient (CRC) was 42 %, 37 % and 34 % for the U-SPECT-II, X-SPECT and NanoSPECT-NSO, respectively. At maximal noise levels of 10 %, a CRCcold of 70 %, 52 % and 42 % were obtained for the U-SPECT-II, X-SPECT and NanoSPECT-NSO, respectively. When acquiring (99m)Tc with the GP collimators, the integral/differential uniformity values were 30 %/14 % for the U-SPECT-II, 50 %/30 % for the X-SPECT and 38 %/25 % for the NanoSPECT-NSO. When using the HR collimators, these uniformity values remained similar for U-SPECT-II and X-SPECT, but not for the NanoSPECT-NSO for which the uniformity deteriorated with larger volumes. We compared three μSPECT systems by acquiring and analysing mouse-sized phantoms including a contrast recovery phantom built in-house offering the ability to measure the hot contrast on a warm background in the submillimetre resolution range. We believe our evaluation addressed the differences in imaging potential for each system to realistically image tracer distributions in mouse-sized objects.

Contrast-noise-ratio (CNR) analysis and optimisation of breast-specific gamma imaging (BSGI) acquisition protocols.

BackgroundBreast cancer is one of the most prevalent forms of cancer in women. Breast-specific gamma imaging (BSGI) is a diagnostic imaging method that uses sestamibi-labelled 99Tc and a dedicated gamma camera to localize malignant lesions in breast tissue. The aim of this study is to investigate if the current acquisition protocol for BSGI at our hospital is optimized for the detection of lesions in our patients.MethodsWe analyzed patient data and performed a phantom study with a Dilon 6800 gamma camera. The patient data were collected from a group of 13 patients (740 MBq 99mTc-sestamibi, four views per patient were dynamically acquired with a frame duration of 30 s per frame and a total acquisition time of 8 min per view). Reduced-time static images were created, and contrast-to-noise ratios of identified hotspots were determined for different acquisition times. For the phantom study, we used a contrast detail phantom to investigate the contrast and resolution properties, within the range of relevant clinical acquisition parameters. The phantom was filled with a concentration of 80 MBq in 500 ml of water, and we dynamically acquired frames for a total acquisition time of 60 min using a general purpose (GP) collimator. To compare the GP collimator with the high-resolution collimator, a second acquisition was made for both collimators with a total acquisition time of 16 min.ResultsThe initial analysis of BSGI scans of the 13 patients showed that a dose reduction by a factor of 3 would not have reduced the number of observable hotspots in each of the acquired views. However, a subsequent systematic analysis of our protocol with a contrast-detail phantom showed that dose reduction results in a lower observability of hotspots, whereas increased doses resulted in a higher observability.ConclusionWe believe that the results of our phantom study are relevant for clinical practice and that further dose reduction cannot be recommended for the BSGI exams at our hospital and that an increase of the administered activity should be considered.

Comparison of gamma (Anger) camera systems in terms of detective quantum efficiency using Monte Carlo simulation

The aim of the present study was to perform an extensive evaluation of available gamma camera systems in terms of their detective quantum efficiency (DQE) and determine their dependency on relevant parameters such as collimator type, imaging depth, and energy window using the Monte Carlo technique. The modulation transfer function was determined from a simulated (99m)Tc point source and was combined with the system sensitivity and photon yield to obtain the DQE of the system. The simulations were performed for different imaging depths in a water phantom for 13 gamma camera systems from four manufacturers. Except at very low spatial frequencies, the highest DQE values were found with a lower energy window threshold of around 130 keV for all systems. The height and shape of the DQE curves were affected by the collimator design and the intrinsic properties of the gamma camera systems. High-sensitivity collimators gave the highest DQE at low spatial frequencies, whereas the high-resolution and ultrahigh-resolution collimators showed higher DQE values at higher frequencies. The intrinsic resolution of the system mainly affected the DQE curve at superficial depths. The results indicate that the manufacturers have succeeded differently in their attempts to design a system constituting an optimal compromise between sensitivity and spatial resolution.

Optimization of the angle between detector modules in a dual-head cardiac SPECT

In recent years, dedicated cardiac single photon emission computed tomography (SPECT) systems have been undergoing a profound change in design with multiple detectors and various angles between the modules to improve the sensitivity and the resolution by reducing the distance between the heart and the detector. The performance of a dual-head cardiac SPECT for small-animal imaging was characterized as a function of the angle between two detector heads by using GATE simulations, and simulation data were validated with experimental results. Each detector head consists of 50 × 50 × 6 mm3 NaI(Tl) optically coupled to a Hamamatsu H8500 position sensitive photomultiplier (PSPMT) and a low-energy high-resolution parallel-hole collimator (LEHR, septal thickness: 0.2 mm, diameter: 1.9 mm). The distance between the collimator surface and the center of rotation was set as 20, 20, 20, 25, or 31.5 mm for 70°, 80°, 90°, 100°, or 110°, respectively, based on a 40-mm field of view (FOV). A point source and a rat cardiac phantom of Tc-99m in scattering media were simulated. Projection data were acquired for 180 angular views in steps of 2° and were reconstructed by using a filtered back-projection algorithm. Results demonstrated that the angle between the detector heads did not make a big difference in the image quality when scattering media were not presented, but the dual heads in the 80° geometry provided the best spatial resolution in the cardiac phantom study. The peak-to-valley ratio between the myocardial wall and the cavity was measured as 1.87, 11.01, 3.28, 3.40, or 2.46 for 70°, 80°, 90°, 100°, or 110°, respectively. Experiments were performed with a dual-head SPECT in the 80° geometry, and the results agreed well with these from the simulations. In this study, the impact of the angle between dual detector heads on the imaging performance was evaluated, and the optimal angle was derived for a dedicated cardiac SPECT.

The effect of type of filters and collimators on the SPECT axis of rotation error

High resolution and artifact free SPECT reconstruction of the distribution of radioactive sources over the entire imaging field requires exact alignment between the electronic and the mechanical axis of rotations. In this paper, the effect of misalignment between the electronic and the mechanical axis of rotations of SPECT system equipped with low-energy high-resolution and low-energy general-purpose collimators through the field of view has been studied. In addition, the useful dimensions of the SPECT field of view without artifact due to axis of rotation error have been calculated. Furthermore, the roles of digital filters in reducing this effect have been studied.

A comparison of different energy window subtraction methods to correct for scatter and downscatter in I-123 SPECT imaging

One of the main problems in quantification of single photon emission computer tomography imaging is scatter. In iodine-123 (I-123) imaging, both the primary 159 keV photons and photons of higher energies are scattered. In this experimental study, different scatter correction methods, based on energy window subtraction, have been compared with each other. Iodine-123 single photon emission computed tomography images of a phantom with a known intensity ratio between background and hollow spheres were acquired for three different collimators (low energy high resolution, low energy general purpose, and medium energy general purpose). The hollow spheres were filled with a higher activity concentration than the uniform background activity concentration, resulting in hot spots. Counts were collected in different energy windows, and scatter correction was performed by applying different methods such as effective scatter source estimation, triple and dual energy window (TEW and DEW), double peak window (DPW) and downscatter correction. The intensity ratio between the spheres and the background was used to compare the performance of the different methods. The results revealed that the efficiency of the scatter correction techniques vary depending on the collimator used. For the low energy high resolution collimator, all correction methods except the effective scatter source estimation and the DPW perform well. For the medium energy general purpose collimator, even without scatter correction, the calculated ratio is close to the real ratio. The DEW and DPW methods tend to overestimate the ratio. For the low energy general purpose collimator, only the DEW and the combined DEW and downscatter correction methods perform well. The only correction method that provides a ratio that differs by less than 5% from the real ratio for all the collimators is the combined DEW and downscatter correction method.

Performance characteristics of a new pixelated portable gamma camera

To evaluate and characterize the performance of a new commercially available pixelated portable gamma camera Ergo (Digirad, Poway, CA). The authors evaluated a pixelated portable gamma camera system, Ergo, that consists of 11 520 elements of 3 × 3 mm(2) CsI(Tl) crystals that are 6-mm thick and are coupled to silicon photodiodes. The detector element has a size of 3.31 × 3.24 mm(2). The gamma camera performance was evaluated for both low-energy all-purpose (LEAP) and low-energy high-resolution (LEHR) collimators. The flood-field uniformity for (99m)Tc and (201)Tl was assessed using fillable uniform flood phantoms. Energy spectra were acquired for (99m)Tc, (111)In, (201)Tl, and (67)Ga to evaluate energy linearity and energy resolution. Spectral fits were performed to calculate the photopeak energies and resolutions. The pixel size and multiwindow spatial registration (MWSR) was evaluated by measuring mixed (99m)Tc and (201)Tl point sources placed at known distances apart. The system's sensitivity was measured according to the National Electrical Manufacturer's Association (NEMA) NU1-2007 standards for both LEAP and LEHR collimators as a function of distance from the collimator surface (5, 10, 15, 20, 25, 30, and 40 cm). The system resolution without scatter was measured for both LEAP and LEHR using (99m)Tc-filled capillary tubes located at 0, 2, 4, 6, 10, and 12 cm away from the surface of the collimator. As a measure of the spatial resolution, the full width at half maximum (FWHM) at a given distance was calculated from the presampling line spread function (LSF), constructed from the line profiles of the capillary tubes at the same distance. As a comparison, the FWHM at 10 cm away from LEHR and LEAP collimators was also calculated from linear interpolation as described by NEMA NU-1 2007 and from fitting the profiles to a Gaussian-plus-constant model. All isotope-collimator pairs demonstrated good flood-field uniformity with an integral uniformity of ≤5% and a differential uniformity of ≤3%. The system demonstrated excellent energy linearity with maximum discrepancy of measured keV from true keV of <1%. The energy resolution of the (99m)Tc 140-keV photopeak was 7.4%. The image pixel size was measured as 3.23 × 3.18 mm(2), and the MWSR was within 0.3 mm (or ~10% of the nominal pixel size). The system sensitivity at 10 cm was 112.6 cps/MBq (249.9 cpm/μCi) for LEAP and 63.1 cps/MBq (140.1 cpm/μCi) for LEHR. The system spatial resolution varied linearly with distance from the collimator and the FWHM were measured to be 7.2 and 8.9 mm at 10 cm for LEHR and LEAP, respectively. Herein, the authors describe detailed performance evaluation procedures of a new pixelated portable gamma camera system, which can also be applied to evaluate other pixelated gamma camera system. Spatial resolution assessment in near-field imaging condition offers a unique challenge where the measured FWHM is highly dependent on relative position between the capillary tube and the detector element. The evaluations of the Ergo gamma camera suggest suitable clinical imaging performance. This portable gamma camera has a high (LEAP) planar sensitivity, high energy and spatial resolutions that are comparable to other available gamma cameras, and it exhibits superior count rate performance that is linear up to tens of millions count per second. The Ergo imaging performance, however, can still be improved, for example, by optimizing collimator design for near field imaging.

Monte carlo study of the effect of collimator thickness on T-99m source response in single photon emission computed tomography

In single photon emission computed tomography (SPECT), the collimator is a crucial element of the imaging chain and controls the noise resolution tradeoff of the collected data. The current study is an evaluation of the effects of different thicknesses of a low-energy high-resolution (LEHR) collimator on tomographic spatial resolution in SPECT. In the present study, the SIMIND Monte Carlo program was used to simulate a SPECT equipped with an LEHR collimator. A point source of 99mTc and an acrylic cylindrical Jaszczak phantom, with cold spheres and rods, and a human anthropomorphic torso phantom (4D-NCAT phantom) were used. Simulated planar images and reconstructed tomographic images were evaluated both qualitatively and quantitatively. According to the tabulated calculated detector parameters, contribution of Compton scattering, photoelectric reactions, and also peak to Compton (P/C) area in the obtained energy spectrums (from scanning of the sources with 11 collimator thicknesses, ranging from 2.400 to 2.410 cm), we concluded the thickness of 2.405 cm as the proper LEHR parallel hole collimator thickness. The image quality analyses by structural similarity index (SSIM) algorithm and also by visual inspection showed suitable quality images obtained with a collimator thickness of 2.405 cm. There was a suitable quality and also performance parameters’ analysis results for the projections and reconstructed images prepared with a 2.405 cm LEHR collimator thickness compared with the other collimator thicknesses.

Dacryoscintigraphy

Dacryoscintigraphy is a grossly underutilized nuclear medicine procedure for assessing the patency of nasolacrimal ducts. It is an alternate noninvasive modality requiring no added expertise when compared with dacryocystography, an invasive radiological counterpart. Dacryocystorhinostomy (DCR) is a surgical procedure in which a patent rhinostomy is made so that a low-pressure lacrimal bypass system is created, thus relieving epiphora, dacryocystitis or mucocele. DCR has been accepted as a highly successful procedure in the management of epiphora from nasolacrimal duct obstruction; however, adverse local effects can reproduce epiphora. This study highlights the utility and simplicity of dacryoscintigraphy in the postoperative setting of DCR, apart from showcasing its high sensitivity and accuracy in localizing the sites of lacrimal drainage obstruction. Fifty-five postoperative patients of DCR were screened. Ten volunteers constituted the control group. One drop (10 μl) of technetium pertechnetate (TcO4) was instilled simultaneously in the outer canthus of both eyes (50-100 μCi). Upright dynamic (8 min) and anterior static images of the eyes (up to 20 min) were acquired on a gamma camera fitted with a high-resolution collimator. Physiological interventions that were used in this study were eye blinking, saline intervention, and lacrimal sac massaging. Out of 40 symptomatic DCR patients, 22 had complete obstruction at the presac level and 18 patients had partial obstruction. Quantitative parameters like tear transit time and lacrimal sac half-life were also calculated. After massage of the lacrimal sac, progression of the tracer was observed in five patients. Premassage and postmassage tear column measurements showed a relative increase of 30.1%. Massage of eight clinically normal ducts showed a relative increase of 2.4% (P=0.06). Statistical analysis using the Fisher test shows very significant concordance between clinical symptoms and dacryoscintigraphy findings in postoperative DCR patients (P<0.0001). The modified McNemar's pair test did not show statistically significant differences between dacryoscintigraphy and the syringing irrigation test. Dacryoscintigraphy is a simple and easy-to-perform investigation providing high sensitivity in epiphora detection in patients after DCR. Interventions play a role in further enhancing the sensitivity of the technique. This study demonstrates the utility of dacryoscintigraphy in detecting subclinical and partial lacrimal duct obstruction with good patient compliance. It provides an easy and effective way of screening families, enabling an early diagnosis. During imaging, a high-resolution collimator is found to be an efficient substitute for the conventional pinhole collimator.

Optimization of a high-resolution collimator for a CdTe detector: Monte Carlo simulation studies

Photon counting detectors using cadmium zinc telluride (CZT) or cadmium telluride (CdTe) have benefits compared to conventional scintillation detectors, and CZT and CdTe have advantageous physical characteristics for nuclear medicine imaging. Recently, many studies have been conducted using these materials to improve the sensitivity and the spatial resolution of the photon counting detector. By using a pixelated parallel-hole collimator, we may be able to improve the sensitivity and the spatial resolution. The purpose of this study was to optimize the design of a collimator to achieve excellent resolution and high sensitivity for a gamma camera system based on the CdTe detector. In this study we simulated a gamma camera system with a photon counting detector based on CdTe and evaluated the system’s performance. We performed a simulation study of the PID 350 (Ajat Oy Ltd., Finland) CdTe detector by using a Geant4 Application for Tomographic Emission (GATE) simulation. This detector consists of small pixels (0.35 × 0.35 mm2). We designed two parallel-hole collimators with different shapes and verified their usefulness. One was the proposed pixelated parallel-hole collimator in which the hole size and the pixel size are the same, and the other was the hexagonal parallel-hole collimator, which had a hole size similar to that of the pixelated parallel-hole collimator. We evaluated the sensitivity, spatial resolution, and contrast resolution to determine which parallel-hole collimator was best for the PID 350 CdTe detector. The average sensitivity was 22.65% higher for the pixelated parallel-hole collimator than for the hexagonal parallel-hole collimator. Also, the pixelated parallel-hole collimator provided 10.7% better spatial resolution than the hexagonal parallel-hole collimator, and the contrast resolution was improved by 8.93%. These results reflect an improvement in sensitivity and spatial resolution, and indicate that the imaging performance of the pixelated parallel-hole collimator is better than that of the hexagonal parallel-hole collimator. In conclusion, we successfully established a high resolution gamma camera system with a pixelated parallel-hole collimator, and based on our results, we recommend using the pixelated parallel-hole collimator to improve the sensitivity and the spatial resolution of gamma camera systems with semiconductor detectors such as CdTe.

Efficacy of high-energy collimator for sentinel node lymphoscintigraphy of early breast cancer patients

IntroductionLymphoscintigraphy is an important part of sentinel node mapping in breast cancer patients. Sometimes star shaped artefacts due to septal penetration can be problematic during imaging. In the current study, we evaluated the possibility of high energy (HE) collimators use for lymphoscintigraphy.Patients and methodsTwenty patients with early breast carcinoma were included. Thirty minutes after radiotracer injection (99mTc-antimony sulphide colloid), anterior and lateral images were acquired using a dual head gamma camera equipped with a parallel hole low energy high resolution (LEHR) collimator on one head and HE collimator on another head. All images were reviewed by two nuclear medicine specialists regarding detectability and number of axillary sentinel nodes and presence of star artefact.ResultsAll images taken by LEHR collimators showed star artefact of the injection site. No image taken by HE collimator showed this effect. In two patients the sentinel node was visible only by HE collimator. Tumour location in both of these patients was in the upper lateral quadrant and both had history of excisional biopsy. In two patients additional sentinel node was visible adjacent to the first one only on the LEHR images.ConclusionsHE collimators can be used for sentinel lymph node mapping and lymphoscintigraphy of the breast cancer patients. This collimator can almost eliminate star-shaped artefacts due to septal penetration which can be advantageous in some cases. However, to separate two adjacent sentinel nodes from each other LEHR collimators perform better.

Comparison between the image qualities obtained with low energy high-resolution (LEHR) and LEGP collimators in single-photon emission computed tomography (SPECT) under implementation of different filters

The aim of a single-photon emission computed tomography (SPECT) filter is to use the sharpest filter/smooth combination consistent with getting quality images. Fourier filtering technique has been shown to greatly improve image quality in both the spatial and temporal domain. An optimal filter manipulates the image in such a way that the image quality is enhanced without losing the basic components of the input object. Many filters have been developed to recover resolution and suppress noise. Thus, the question of theoptimal filter selection has been the subject of this investigation. The selection of proper collimator in many application of SPBCT will contribute to optimal image quality and quantitative information within the characteristics of the imaging equipment. In this study, we compared the results obtained by utilization of low energy high-resolution (LEHR) and low energy general-purpose (LEGP) collimators, under implementation of various filters, to show effect of hardware and software filters on the image quality, and capability of mathematical tools to compensate for the hardware flaw. Key words: Single-photon emission computed tomography (SPECT), filter, low energy high-resolution (LEHR) collimator, low energy general-purpose (LEGP).

Joint optimization of collimator and reconstruction parameters in SPECT imaging for lesion quantification

Obtaining the best possible task performance using reconstructed SPECT images requires optimization of both the collimator and reconstruction parameters. The goal of this study is to determine how to perform this optimization, namely whether the collimator parameters can be optimized solely from projection data, or whether reconstruction parameters should also be considered. In order to answer this question, and to determine the optimal collimation, a digital phantom representing a human torso with 16 mm diameter hot lesions (activity ratio 8:1) was generated and used to simulate clinical SPECT studies with parallel-hole collimation. Two approaches to optimizing the SPECT system were then compared in a lesion quantification task: sequential optimization, where collimation was optimized on projection data using the Cramer–Rao bound, and joint optimization, which simultaneously optimized collimator and reconstruction parameters. For every condition, quantification performance in reconstructed images was evaluated using the root-mean-squared-error of 400 estimates of lesion activity. Compared to the joint-optimization approach, the sequential-optimization approach favoured a poorer resolution collimator, which, under some conditions, resulted in sub-optimal estimation performance. This implies that inclusion of the reconstruction parameters in the optimization procedure is important in obtaining the best possible task performance; in this study, this was achieved with a collimator resolution similar to that of a general-purpose (LEGP) collimator. This collimator was found to outperform the more commonly used high-resolution (LEHR) collimator, in agreement with other task-based studies, using both quantification and detection tasks.