High-resolution Collimator Research Articles

Faster Acquisition for Dopamine Transporter Imaging Using Swiftscan Step and Shoot Continuous SPECT Without Impairing Visual and Semiquantitative Analysis.

Aim: Dopamine transporter (DAT) imaging with [123I] FP-CIT (DaTSCAN) is an established diagnostic tool in parkinsonism and dementia. Using a low energy high resolution and sensitivity (LEHRS) collimator and step and shoot continuous scanning mode, Swiftscan single photon emission computed tomography (SPECT) (GE Healthcare) enhances sensitivity and enables time or dose reduction. In this phantom and clinical study, we aim to validate a 25% reduction of the acquisition time using Swiftscan and its lack of effect on visual or quantitative analysis.Methods: Anthropomorphic striatal phantom with fillable striata was used. SPECT data from 30 normals (12 men, 18 women; age range, 39–91 years; mean, 71 years ± 11) and 30 patients with Parkinson disease or other neurodegenerative disease with extra-pyramidal syndrome (16 men, 14 women; age range, 43–84 years; mean, 69 years ± 10) were also included. Both phantom and clinical data were acquired using Swiftscan and reconstructed with full-time and 25%-time reduction. Striatal binding ratios (SBRs) were calculated using DaTQUANT software.Results: Both in phantom experiments and in clinical cases, visual analysis remained stable and SBRs were not significantly different whether using Swiftscan or Swiftscan with 25%-time reduction (p < 0.001). There was an excellent inter-rater agreement and no effect of time reduction on diagnosis or on image quality.Conclusion: Using Swiftscan step and shoot continuous SPECT mode, 25%-time reduction can be applied to DaTSCAN acquisition protocols, without impairing visual or quantitative analysis.

Comparison of Low-Pass Filters for SPECT Imaging.

In single photon emission computed tomography (SPECT) imaging, the choice of a suitable filter and its parameters for noise reduction purposes is a big challenge. Adverse effects on image quality arise if an improper filter is selected. Filtered back projection (FBP) is the most popular technique for image reconstruction in SPECT. With this technique, different types of reconstruction filters are used, such as the Butterworth and the Hamming. In this study, the effects on the quality of reconstructed images of the Butterworth filter were compared with the ones of the Hamming filter. A Philips ADAC forte gamma camera was used. A low-energy, high-resolution collimator was installed on the gamma camera. SPECT data were acquired by scanning a phantom with an insert composed of hot and cold regions. A Technetium-99m radioactive solution was homogenously mixed into the phantom. Furthermore, a symmetrical energy window (20%) centered at 140 keV was adjusted. Images were reconstructed by the FBP method. Various cutoff frequency values, namely, 0.35, 0.40, 0.45, and 0.50 cycles/cm, were selected for both filters, whereas for the Butterworth filter, the order was set at 7. Images of hot and cold regions were analyzed in terms of detectability, contrast, and signal-to-noise ratio (SNR). The findings of our study indicate that the Butterworth filter was able to expose more hot and cold regions in reconstructed images. In addition, higher contrast values were recorded, as compared to the Hamming filter. However, with the Butterworth filter, the decrease in SNR for both types of regions with the increase in cutoff frequency as compared to the Hamming filter was obtained. Overall, the Butterworth filter under investigation provided superior results than the Hamming filter. Effects of both filters on the quality of hot and cold region images varied with the change in cutoff frequency.

Optimal VMAT Delivery for Elekta MLC Beam Modulator: A Study of Collimator Rotation for Head and Neck Planning

BackgroundWell-optimized treatment planning parameters are vital for optimum beam delivery in advanced radiotherapy techniques. The Elekta “Beam-Modulator” (BM) is a high-resolution multileaf collimation system where each individual leaf is 4 mm wide at the isocentre, without backup diaphragms and jaws. Its maximum aperture is 21 × 16 cm2, which results in a limited clinical use for the target geometry of maximum 20 cm in length. The collimator rotation provides an opportunity to treat slightly extended treatment length with optimal target coverage. The study aims to observe the collimator rotation influence on volumetric modulated arc therapy (VMAT) plan quality for different head and neck target geometries using limited field collimator of BM. MethodsTen patients with head and neck cancer were planned by means of simultaneous integrated boost to deliver VMAT for five patients with three dose levels (70/60/56) and five patients with two dose levels (60/54). The single arc, dual arc, and combined two independent single arcs of 356° each were well optimized for four collimator angles (C) 15°,30°, 45°, and 90°. The plans were prepared for BM with SmartArc module of Pinnacle³ treatment planning system. Statistical significance (P ≤ .05) among collimator angles for planning target volume dose-volume indices was calculated with Student's t-test. Organ-at-risk doses were compared and monitor units were also evaluated as a parameter for dose-delivery efficiency and out-of-field dose index. ResultsThe dual arc and combined two independent single arcs achieved planning objectives for C15°, C30°, and C45°. Single arc for all collimator angles and C90° for all VMAT schemes failed to achieve planning objectives. The spread of low dose bath 20, 35, and 40 Gy and deterioration of doses were higher towards periphery at C90° and statistically significant. ConclusionThe small and medium collimator angles for dual-arc VMAT scheme(s) are suitable, whereas single arc and C90° are not suitable in VMAT implementation for Elekta Beam-Modulator collimation system.

Impact of Collimator on DaT-SPECT Imaging: Monte Carlo Simulation Study

Aim: The purpose of this study was to assess the impact of the collimator in viewing the dopamine transporter, using 123I ioflupane single-photon emission computed tomography (DaT-SPECT) images utilizing a Monte Carlo simulation. Methods: For the purpose of this study, the Monte Carlo simulation of electrons and photons (MCEP)- SPECT was used. A numerical phantom was created from a real basal ganglia phantom and installed within the code. The specific binding ratios (SBRs) were 5.03 and 2.01 for the background concentration of 7.44 kBq/mL or 7.04 and 3.03 for a background concentration of 5.56 kBq/mL. The simulated images were evaluated using a recovery coefficient (RC). Initially, we simulated the performance of 14 collimators without resolution correction to investigate the impact of the collimator dimension. The effects of two resolution correction methods (collimator broad correction (CBC) and three-dimensional frequency– distance relationship (3D-FDR)) on two reconstruction methods (Ordered-Subsets Expectation Maximization (OSEM) and Filtered back projection (FBP)) was assessed for collimators that demonstrated a better RC value. Results: Five low-energy high-resolution (LEHR) collimators and one medium-energy general-purpose (MEGP) collimator demonstrated superior RC values. These collimators had a high aspect ratio (holelength/hole-diameter). The maximum RC value without resolution correction was 64.9% when the image was reconstructed with OSEM. The RC value improved to 79.7% when the resolution correction of CBC was applied. When the resolution collection was applied, the RCs improved by approximately 1.2 times when compared against those without the resolution correction. In terms of the reconstruction method, the RC obtained using OSEM was statistically insignificant when compared to the RC using FBP. The difference in the RC value with collimators decreased according to resolution correction. Conclusion: The LEHR collimator with a high aspect ratio, and the OSEM with spatial resolution correction were confirmed to be appropriate for DaT-SPECT imaging. In terms of the reconstruction method, CBC was more favourable than FDR.

Optimization of Scatter Correction Method in Samarium-153 Single-photon Emission Computed Tomography using Triple-Energy Window: A Monte Carlo Simulation Study.

Purpose:In single-photon emission computed tomography imaging, the presence of scatter degrades image quality. The goal of this study is to optimize the main- and sub-energy windows for triple-energy window (TEW) method using Monte Carlo SImulating Medical Imaging Nuclear Detectors (SIMIND) code for samarium-153 (Sm-153) imaging.Materials and Methods:The comparison is based on the Monte Carlo simulation data with the results estimated using TEW method. Siemens Symbia gamma-camera equipped with low-energy high-resolution collimator was simulated for Sm-153 point source located in seven positions in water cylindrical phantom. Three different main-energy window widths (10%, 15%, and 20%) and three different sub-energy window widths (2, 4, and 6 keV) were evaluated. We compared the true scatter fraction determined by SIMIND and scatter fraction estimated using TEW scatter correction method at each position. In order to evaluate the image quality, we used the full width at half maximum (FWHM) computed on the PSF and image contrast using Jaszczak phantom.Results:The scatter fraction using TEW method is similar to the true scatter fraction for 20% of the main-energy window and 6 keV sub-energy windows. For these windows, the results show that the resolution and contrast were improved.Conclusion:TEW method could be a useful scatter correction method to remove the scatter event in the image for Sm-153 imaging.

Energy Window and Collimator Optimization in Lutetium-177 Single-photon Emission Computed Tomography Imaging using Monte Carlo Simulation.

Introduction:In lutetium-177 (Lu-177) single-photon emission computed tomography (SPECT) imaging, the accuracy of activity quantification is degraded by penetrated and scattered photons. We assessed the scattered photon fractions in order to determine the optimal situation and development of correction method. This study proposes to compare the image quality that can be achieved by three collimators.Materials and Methods:Siemens Medical System Symbia fitted with high-energy (HE), medium-energy (ME), and low-energy high-resolution collimators was simulated using the SIMIND Monte Carlo code simulation code. Counts were collected in three different main-energy window widths (20%, 15%, and 10%) for Lu-177 point source. Primary and scattered point spread functions and also geometric, penetration, scattering were drawn and analyzed.Results:In Lu-177 imaging, a 20% of main-energy window and ME collimator were found to be optimal. HE collimator can be used when the resolution is not required.Conclusion:These results provide the optimal energy window and collimator in Lu-177 SPECT imaging and will help the quantification of Lu-177.

Comparison of acquisition protocols for ventilation/perfusion SPECT—a Monte Carlo study

One of the most commonly used imaging techniques for diagnosing pulmonary embolism (PE) is ventilation/perfusion (V/P) scintigraphy. The aim of this study was to evaluate the performance of the currently used imaging protocols for V/P single photon emission computed tomography (V/P SPECT) at two nuclear medicine department sites and to investigate the effect of altering important protocol parameters.The Monte Carlo technique was used to simulate 4D digital phantoms with perfusion defects. Six imaging protocols were included in the study and a total of 72 digital patients were simulated. Six dually trained radiologists/nuclear medicine physicians reviewed the images and reported all perfusion mismatch findings. The radiologists also visually graded the image quality.No statistically significant differences in diagnostic performance were found between the studied protocols, but visual grading analysis pointed out one protocol as significantly superior to four of the other protocols. Considering the study results, we have decided to harmonize our clinical protocols for imaging patients with suspected PE. The administered Technegas and macro aggregated albumin activities have been altered, a low energy all purpose collimator is used instead of a low energy high resolution collimator and the acquisition times have been lowered.

Monte Carlo assessment of coded aperture tool for breast imaging: a Mura-mask case study

The main purpose of this work was to perform a rigorous computational study on scintimammography with a Mura-mask based on Monte Carlo simulation of voxelized breast phantoms. Three main objectives were addressed: (1) verification of Geant4 version 10.4, (2) optimization of the imaging setup, and (3) small tumor detection and localization. We successfully verified the Geant4-based imaging of a commonly used phantom in the field. We used a Mura-mask with a $$41\times 41$$ array pattern with adjustable thickness, material, and hole shape (box and cylinder); a low-energy high-resolution collimator with different hole shapes (cylinder and hexagon); and a voxelized breast phantom with different sizes (small, medium, and large) and glandularity percentages (low, medium, and high). We also compared the detector crystal outputs of CdZnTe and NaI(Tl). The simulation was followed by a deconvolution procedure, and the data (images) were statistically emphasized. Statistical metrics indicate that the Mura-mask (W material with 1.5 mm thickness and box holes) combined with a CdZnTe detector leads to the optimum point spread function. Finally, a preliminary study on small-sized tumor detection and localization was conducted with different tumor-to-background ratios (from 2 to 12). Tumors with diameters of 5 and 8 mm could be detected, while those of 2 mm were undetectable. Nevertheless, this study enhances our understanding of the early detection of tumors in the field of scintimammography.

The role of 99mTc-MIBI in the evaluation of non-functional thyroid gland nodules

Aim: The objective of the study is to show the role of 99mTc methoxyisobutylisonitrile (99mTc-MIBI) with planar imaging and single photon emission tomography with “low dose” CT (SPECT-CT) in a work up of non-functioning thyroid nodules on imaging with 99mTc- pertechnetate, which were confirmed by ultrasound examination. Patients and methods: Patients who underwent thyroid imaging with 99mTc-MIBI in the period from 2008 to 2018 were reviewed. The findings were compared with PHD results. The imaging was performed on gamma camera with high resolution collimator as planar scintigraphy and SPECT-CT. The results of fine needle aspiration biopsy were classified by the Bethesda classification, while PHD results were classified, as benign or malignant. Results: In the period from 2008-2018, 271 thyroid imaging with 99mTc- MIBI were performed. In 42 patients all-inclusive criteria were met.Out of those 42 patients, 28 of the PHD findings were concordant with the imaging, i.e. a node was presented as hypermetabolic. The calculated negative predictive value of the procedure is 78.6% (NPV = 11/ (3+11) = 0,786), and positive predictive value 18% (PPV = 5/ (5+23) = 0.179). Conclusion: Given the high negative predictive value, obtained from our results, 99mTc -MIBI imaging may be recommended as a complementary diagnostic method to fine-needle aspiration (FNA) in work up of thyroid nodules.

Comparison of Image Quality of Different Radionuclides Technetium-99m, Samarium-153, and Iodine-123.

Introduction:The choice of the radionuclide has a key role in nuclear medicine which appearing the lowest scatter fraction. In addition, the presence of penetrated and scattered photons from collimator in single-photon emission computed tomography images degrades resolution and contrast. Thus, image quality depends on sensitivity and resolution of the collimator–detector system. The goal of this study was to compare the image quality that can be achieved by three radionuclides: technetium-99 m (Tc-99 m), iodine-123 (I-123), and samarium-153 (Sm-153).Materials and Methods:Tc-99 m and Sm-153 were imaged with low-energy high resolution (LEHR) collimator, while I-123 was imaged with medium-energy (ME) collimator. We modeled the Siemens Symbia Medical system using Monte Carlo simulation code SIMIND. The imaging characteristics of each radionuclide were investigated by simulated data: point spread function, sensitivity (Cps/MBq) and geometric, penetration and scattering distribution.Results:Tc-99 m and Sm-153 give best and results with LEHR collimator for spatial resolution (full width at half maximum [FWHM] = 3.19 mm; full width at tenth maximum [FWTM] = 6.73 mm) and (FWHM = 3.22 mm; FWTM = 7.39 mm), respectively. Whereas, I-123 provided with ME collimator a lower resolution (FWHM = 4.89 mm; FWTM = 9.89 mm). The sensitivity recorded by Tc-99 m, Sm-153, and I-153 were (31.21 Cps/MBq), (10.16 Cps/MBq), and (51.22 Cps/MBq), respectively.Conclusion:Tc-99 m and Sm-153 give the best and generally similar imaging properties with LEHR. For I-123, the ME collimator helps lowering the influence of high-energy gamma rays.

Simplified Dynamic Phantom for Pediatric Renography: A Description of Instrument and its Performance.

Objective(s):Renography is used for the diagnostic evaluation of pediatric patients with a suspected obstruction of urinary tract or impaired renal function. The recommended dose for children have been released by the European Association of Nuclear Medicine, Society of Nuclear Medicine and Molecular Imaging, and Japanese Society of Nuclear Medicine. Since acquisition counts in dynamic scintigraphy are affected by the administered doses and sensitivity of the scintillation camera, the scan procedure should be determined independently. In this study, we constructed simplified dynamic phantom imitating pediatric renography and tested its performance.Methods: Simplified dynamic phantom consisted of three components (i.e., infusion, imitated kidney, and drainage sections). The infusion rates (mL/min) were determined by comparing the time activity curves obtained from patients with normal renal function. The time-points of the maximum counts (Tmax), as well as the two-thirds and one-half of the maximum counts (T2/3 and T1/2) were measured in different doses using the phantom with the best-match infusion rate and duration, and low-energy general-purpose (LEGP) or low-energy high-resolution (LEHR) collimators and applying different attenuations.Results:The best-match infusion rates of the phantom to imitate the time activity curve of the normal renal function were 42.0, 1.0, 0.6, and 0.3 mL/min in the arterial, secretory, early-excretory, and late-excretory phases, respectively. When 30 MBq, LEHR collimator and non-water-equivalent phantom were applied, Tmax, T2/3, and T1/2 were 242±15.3, 220±10.0 and 317±25.2 seconds, respectively. Using LEGP collimator and (3 MBq of activity) 5-cm water-equivalent phantom, Tmax, T2/3, and T1/2 values were estimated as 242±5.8, 213±11.5, and 310±17.3 sec, respectively.Conclusion:Our simplified dynamic phantom for pediatric renography could imitate the time activity curves obtained from patients with normal renal function. Tmax, T2/3, and T1/2 could be measured under various settings of dose, collimator, and tissue attenuation.

Impact of Novel Incorporation of CT-based Segment Mapping into a Conjugated Gradient Algorithm on Bone SPECT Imaging: Fundamental Characteristics of a Context-specific Reconstruction Method.

Objective(s):The latest single-photon emission computed tomography (SPECT)/computed tomography (CT) reconstruction system, referred to as xSPECT Bone™, is a context-specific reconstruction system utilizing tissue segmentation information from CT data, which is called a zone map. The aim of this study was to evaluate the effects of zone-map enhancement incorporated into the ordered-subset conjugated gradient minimization (OSCGM) reconstruction method on SPECT images.Methods: Image quality with zone-map enhanced OSCGM (OSCGMz) and non-enhanced OSCGM methods was compared using various reconstruction parameters. The compartment phantom had 3 radioactive sections with CT values of about 1000, 250, and 0 HU. SPECT data were acquired using a low-energy high-resolution (LEHR) collimator, with a 256×256 matrix and 2.4-mm pixel size. The performances of the 2 reconstruction methods (OSCGM vs. OSCGMz) were evaluated on the basis of %error, coefficient of variation (%CV), and normalized mean squared error (NMSE), and adequate iterative update numbers were determined. The relative CV representing the ratio of smoothed images to non-smoothed images was calculated to evaluate the effects of the Gaussian filter on each section set with different CT values.Results:On comparing the OSCGM and OSCGMz methods, it was found that the %error of the OSCGMz method tended to show convergence with fewer updates, especially in the high CT value section mimicking bone absorption. In the water section, the %CV of the OSCGMz method was lower than that of the OSCGM method. The NMSE minimum values for the OSCGM and OSCGMz methods were obtained at 30 and 20 updates, respectively. The relative CV for the OSCGMz method in the water section decreased remarkably according to the size of the full width at half maximum (FWHM) of the Gaussian filter.Conclusion:The zone-map enhancement contributed to SPECT reconstruction for the reproduction of radioactive concentrations in bone tissues, using a low number of OSCGM updates. Our findings indicated that the incorporation of zone maps into SPECT reconstruction might improve image quality.

Comparison of automatic depth correction versus manual depth correction in the calculation of glomerular filtration rate in gates renal processing of diethylenetriaminepentaacetic acid renogram in prospective renal donors

Aim: The aim of the study was to compare the glomerular filtration rate (GFR) obtained by gates method of renal processing using automated system generated method (ASGM) of depth correction with manual depth correction method (MDCM), in prospective renal donors using 99m-Tc diethylenetriaminepentaacetic acid (DTPA) scintigraphy. Materials and Methods: Prospective interventional study involving 20 voluntary renal donors of age 26–65 years were included. 99m-Tc DTPA renograms were acquired by dynamic acquisition for 30 min. Presyringe and postsyringe counts, prevoid and postvoid images, and both sides of lateral images (for manual depth correction) were acquired. GFR was calculated by Gates renal processing with the depth correction both by ASGM and MDCM methods. Results: The mean depth of right and left kidneys calculated by MDCM and ASGM were 7.2 ± 1.1 and 6.4 ± 1.1 and 7.0 ± 1.2 and 6 ± 1.2, respectively. The mean total GFR calculated by Gate's Method using MDCM and ASGM was 96.2 ± 15.4 and 82.0 ± 11.5. There was a statistically significant difference in the depth correction of both kidneys and improvement in total GFR values by MDCM methods compared to the ASGM method. Conclusion: There was a significant difference in depth and GFR values, calculated from MDCM compared to ASGM. Hence, the MDCM is better in calculating GFR for renal donors, especially when using low-energy high-resolution collimators, as full-width half-maximum varies considerably for every centimeter of the distance of the source from the collimator.

61 Evaluation and comparison of a new low energy high resolution collimator

Introduction In order to find an optimum compromise between spatial resolution and sensitivity, GEHC designed a new collimator (LEHRS) and combined it to a new acquisition software for planar images (Clarity2D) and to a new tomographic acquisition method: ”step and shoot continuous”. The objective of the study is to evaluate planar and tomographic performances of this new collimator and to compare them to GEHC LEHR and to Siemens LEHR. Methods In planar mode, sensitivity and spatial resolution were measured for the three collimators according to NEMA NU1–2000 [1] . In tomographic mode, volumetric sensitivity and spatial resolution were also evaluated according to NEMA NU1–2000. Image quality was measured according NEMA NU2-2012 (contrast of 8) [2] . Projections were acquired according to routine protocols and the volumes were reconstructed thanks to and independent software taking into account spatial resolution depth dependence and attenuation correction. Results Planar mode. Maximum sensitivity was measured for Siemens LEHR (100 cps/MBq), LEHRS’s was 9% lower and GEHC LEHR’s was 22% lower. The full width at half maximum of the linear spread function, at source contact, is equivalent for both LEHR and 5% higher for LEHRS. Nevertheless thanks to Clarity2D, LSF’s FWHM degradation is less important when collimator distance increases. With 15 cm of diffusing material, LEHRS spatial resolution is 9,2 mm, GEHC LEHR is 10,1 mm and Siemens LEHR is 10,6 mm. Tomographic mode. LEHRS volumetric sensitivity is superior to both LEHR’s (16% for Siemens LEHR and 25% for GEHC LEHR). Spatial resolution is equivalent for the 3 collimators. The biggest hot sphere contrast recovery is equivalent for both GEHC collimators (41% for LEHR and 39,3% for LEHRS) and superior to Siemens LEHR (35,7%). LEHRS provides a better background variability (7,9%) than both LEHR (10,1% for GEC and 9,8% for Siemens). Conclusions In planar mode, LEHRS collimator associated to clarity 2D provides higher quality images than the other collimators since then enough diffusing material is placed between the source and the camera. In tomographic mode, the increase of volumetric sensitivity allows to reduce noise in the images (low background variability) while maintaining equivalent or superior contrast recovery and spatial resolution.

Myocardial MIBG scintigraphy in genetic Parkinson's disease as a model for Lewy body disorders.

To identify myocardial sympathetic denervation patterns suggestive of Lewy body (LB) pathology in patients with genetic and idiopathic parkinsonisms by 123I-metaiodobenzylguanidine (MIBG) scintigraphy. We retrospectively analysed myocardial MIBG images acquired with a dual-head gamma camera and low-energy high-resolution collimator (LEHR) in 194 patients with suspected synucleinopathy or atypical parkinsonism, including 34 with genetic Parkinson's disease (PD; 4 PARK1, 8 PARK2 and 22 PARK8), 85 with idiopathic PD (iPD), 6 with idiopathic REM sleep behaviour disorder (iRBD), 17 with dementia with LB (DLB), 40 with multiple system atrophy (MSA) and 12 with progressive supranuclear palsy (PSP), and in 45 healthy controls. We calculated heart-to-mediastinum MIBG uptake ratios (HMR) at 15min and 4h (HMR4H) for the LEHR and standardized medium-energy collimators, to obtain classification accuracies and optimal cut-off values for HMR using supervised classification and ROC analyses. While patients with LB disorders had markedly lower HMR4HLEHR than controls (controls 1.86 ± 0.26, iPD 1.38 ± 0.29, iRBD 1.23 ± 0.09, PARK1 1.20 ± 0.09, DLB 1.17 ± 0.11; p < 0.05), for the remaining patient categories differences were smaller (PARK8 1.51 ± 0.32; p < 0.05) or not significant (MSA 1.82 ± 0.37, PSP 1.59 ± 0.23, PARK2 1.51 ± 0.30; p > 0.05). The diagnostic accuracy of HMR4HLEHR was highest in patients with LB disorders (PARK1, iPD, DLB, iRBD; 89% to 97%) and lowest in those with PARK2, PARK8, PSP and MSA (65% to 76%), with an optimal HMR4HLEHR cut-off value of 1.72 for discriminating most patients with LB disorders including iPD and 1.40 for discriminating those with aggressive LB spectrum phenotypes (DLB, PARK1 and iRBD). Our study including patients with a wide spectrum of genetic and idiopathic parkinsonisms with different degrees of LB pathology further supports myocardial MIBG scintigraphy as an accurate tool for discriminating patients with LB spectrum disorders.

Molecular imaging using the theranostic agent 197(m)Hg: phantom measurements and Monte Carlo simulations

BackgroundRadiomercury 197mHg and 197Hg, henceforth referred to as 197(m)Hg, is a promising theranostic radionuclide endowed with properties that allow diagnostic and therapeutic applications. The aim of this work was to investigate the capabilities of 197(m)Hg for nuclear medicine imaging. Therefore measurements were performed by using a Philips BrightView SPECT camera. Furthermore, Monte Carlo simulations using the GATE software were performed to theoretically explore the imaging contribution from the various gamma and X-ray emissions from 197(m)Hg for a commercial clinical camera with low-energy high-resolution (LEHR) and high-energy general-purpose (HEGP) collimators. We estimated the spatial resolution by using a four-quadrant bar phantom, and we evaluated the planar and tomographic images from an abdominal phantom containing three cylindrical sources of 197(m)Hg solution.ResultsA good accordance between measurements and simulations was found for planar and SPECT imaging. Simulations allowed the decomposition of the detected energy spectrum into photon origins. Measurements and simulations for the bar phantom revealed that for the LEHR collimator, the 6-mm pattern could be resolved, whereas for the HEGP collimator, the resolution is about 10 mm. Furthermore, we found that no significant image distortion results from high-energy photons when using the LEHR collimator.ConclusionsWe demonstrated the imaging capabilities of 197(m)Hg which is essential both for diagnostic applications and to determine the in vivo biodistribution for dose calculations in therapeutic applications.

OA107] Validation of left ventricular ejection fraction with gated IQ-SPECT myocardial perfusion imaging

Purpose This study was motivated by the inconsistency reported in myocardial perfusion imaging (MPI) studies both in phantom and in patients in the reported ejection fraction (EF) and perfusion indexes between gamma cameras equipped with confocal collimators (IQ-SPECT) and conventional low-energy high-resolution (LEHR) collimation protocols. The aim of the study was to assess in patients the agreement between the EF values and perfusion indexes obtained with IQ-SPECT and reconstructed with iterative reconstruction algorithms and with a conventional gamma camera equipped with LEHR (CGC) and reconstructed with Filtered Backprojection (FBP), considered as the gold standard. Methods Gated-stress myocardial perfusion imaging (MPI) was performed in 56 patients with suspected coronary artery disease. The patients underwent in a random order two sequential acquisitions performed on Symbia-IQ SPECT (4.8 mm pixel size, 1.6°/step, 28”/step, 208° angular range, reconstructed with OSEM, 10x3 iterations, 10 mm-Gaussian filter) and on a Ecam SPECT equipped with LEHR collimators (6.6 mm pixel size, 2.6°/step, 25”/step, 180 angular range, reconstructed with FBP, Butterworth filter 8–0.45); a subset of 32 patients underwent in a separate day a Gated-rest MPI, after injection of an average 524 ± 44 MBq of 99mTc-tetrofosmin. EF values and perfusion indexes (summed stress score-SSS, summed rest score-SRS), were evaluated separately for stress and rest MPI and compared as (CGC-IQ) using Bland–Altman plots estimating the bias and the limits of agreement. Results For EF, the bias were −4.1% −2.1% and the limits of agreement ranged from −18.0% to 9.9% and from −18.2% to 14.1% for stress and rest MPI, respectively. For SSS, bias and limits of agreement were 2.7 and [−9.9; +15.3] and for SRS they were 2.0 and [−5.8; +9.8]. Conclusions IQ configuration overestimates EF values for both stress and rest studies with bias of 2–4% and a considerable amplitude in LA interval that spans about 30%. Thus, there is a tendency to overestimate EF with IQ-SPECT. Of still more concern, is that the limits of agreement between the CGC and IQ are wide indicating that the reconstructed datasets are not interchangeable, and the values obtained with IQ-SPECT should only be used with caution when evaluating the functional state of the heart.

Feasibility study of a novel general purpose CZT-based digital SPECT camera: initial clinical results

BackgroundThe performance of a prototype novel digital single-photon emission computed tomography (SPECT) camera with multiple pixelated CZT detectors and high sensitivity collimators (Digital SPECT; Valiance X12 prototype, Molecular Dynamics) was evaluated in various clinical settings.Images obtained in the prototype system were compared to images from an analog camera fitted with high-resolution collimators. Clinical feasibility, image quality, and diagnostic performance of the prototype were evaluated in 36 SPECT studies in 35 patients including bone (n = 21), brain (n = 5), lung perfusion (n = 3), and parathyroid (n = 3) and one study each of sentinel node and labeled white blood cells. Images were graded on a scale of 1–4 for sharpness, contrast, overall quality, and diagnostic confidence.ResultsDigital CZT SPECT provided a statistically significant improvement in sharpness and contrast in clinical cases (mean score of 3.79 ± 0.61 vs. 3.26 ± 0.50 and 3.92 ± 0.29 vs. 3.34 ± 0.47 respectively, p < 0.001 for both). Overall image quality was slightly higher for the digital SPECT but not statistically significant (3.74 vs. 3.66).ConclusionCZT SPECT provided significantly improved image sharpness and contrast compared to the analog system in the clinical settings evaluated. Further studies will evaluate the diagnostic performance of the system in large patient cohorts in additional clinical settings.

Effects of Varying Matching Between Collimator Hole and Scintillator Pixel on Gamma Camera Image Resolution

A collimator is a key component of gamma cameras, which affects imaging performance significantly. Recently, pixelated scintillator arrays are widely applied in the development of highresolution gamma cameras, instead of monolithic scintillator blocks. Therefore, combining the collimator and the pixelated scintillator has been a crucial factor in achieving good imaging performance. In this study, we investigated the effects of the shape and position of a collimator hole on the image resolution of a gamma camera with a pixelated scintillator. We designed a pixel-matched collimator and a low-energy high-resolution (LEHR) collimator with hexagonal shaped holes that have the same collimator geometrical efficiency. Simulation experiments were performed with a Monte Carlo simulation package (GATE v7.0). For both types of collimator, camera sensitivity was measured for validating the collimator efficiency, and planar images were obtained to measure spatial resolution, with changing the line profile angle based on the septa direction. Camera sensitivities for both collimators were equivalent (difference = 1.76 ± 0.51%). In contrast to the case of the pixel-matched collimator, in the case of the LEHR collimator, as the angle of the line profile varied, the spatial resolution showed a difference at each profile angle. In the case when two collimator holes symmetrically matched with one scintillator pixel, the spatial resolution showed a 64.87% difference in its maximum and a position distortion of 26.06% from the original source position, according to the profile angle, compared to the other unmatched cases. These results showed that using a pixel-matched collimator in gamma camera systems employing a pixelated scintillator is essential for the exact delineation of small regions using high resolution gamma camera imaging

Evaluation of the Reconstruction Parameters of Brain Dopamine Transporter SPECT images Obtained by a Fan Beam Collimator: A Comparison with Parallel-hole Collimators.

Objective(s):The purpose of this study was to examine the optimal reconstruction parameters for brain dopamine transporter SPECT images obtained with a fan beam collimator and compare the results with those obtained by using parallel-hole collimators. Methods:Data acquisition was performed using two SPECT/CT devices, namely a Symbia T6 and an Infinia Hawkeye 4 (device A and B) equipped with fan-beam (camera A-1 and B-1), low- and medium-energy general-purpose (camera A-2 and B-2), and low-energy high-resolution (camera A-3 and B-3) collimators. The SPECT images were reconstructed using filtered back projection (FBP) with Chang’s attenuation correction. However, the scatter correction was not performed. A pool phantom and a three-dimensional (3D) brain phantom were filled with 123I solution to examine the reconstruction parameters. The optimal attenuation coefficient was based on the visual assessment of the profile curve, coefficient of variation (CV) [%], and summed difference from the reference activity of the pool phantom. The optimal Butterworth filter for the 3D-brain phantom was also determined based on a visual assessment. The anthropomorphic striatal phantom was filled with 123I solution at striatum-to-background radioactivity ratios of 8, 6, 4, and 3. The specific binding ratio (SBR) of the striatum (calculated by the CT method) was used to compare the results with those of the parallel-hole collimators.Results:The optimal attenuation coefficients were 0.09, 0.11, 0.05, 0.05, 0.11, and, 0.10 cm-1 for cameras A-1, A-2, A-3, B-1, B-2, and B-3, respectively. The cutoff frequencies of the Butterworth filter were 0.32, 0.40, and 0.36 cycles/cm for camera A, and 0.46, 0.44, and 0.44 cycles/cm for camera B, respectively. The recovery rates of the SBRmean with camera A were 51.2%, 49.4%, and 45.6%, respectively. The difference was not statistically significant. The recovery rates of the SBR with camera B were 59.2%, 50.7%, and 50.8%, respectively. Camera B-1 showed significantly high SBR values.Conclusion:As the findings indicated, the optimal reconstruction parameters differed according to the devices and collimators. The fan beam collimator was found to provide promising results with each device.