[Evaluation of Post-reconstruction Filtering in Resolution Recovery Reconstruction for Bone SPECT Imaging].

PURPOSE: The aim of this study was to clarify the optimal post-reconstruction filtering type in the three- dimensional ordered subset expectation maximization (3D-OSEM) method for bone single photon emission computed tomography (SPECT) from image quality and quantitative values. METHOD: We scanned a National Electrical Manufactures Association's body phantom for bone SPECT filled with radioactive solution of 99mTc whose radioactivity concentration was accurately measured. The SPECT images were created using the 3D-OSEM method. Post-reconstruction filtering was performed using a Butterworth filter (BW), a Gaussian filter (GA), and a Hanning filter (HA) with various parameters. The image quality was evaluated by the normalized mean-squared error (NMSE) value and % of contrast-to-noise ratio (QNR17). The image quality was evaluated by the error values between the measured radioactivity concentration and the true radioactivity concentration in the BG region and insert sphere. RESULTS: The minimum NMSE values were 0.034 (BW), 0.036 (GA), and 0.035 (HA), and there was no difference depending on the filter type. The values of QNR17 were 2.5 (BW), 2.6 (GA), and 2.6 (HA), and there was no difference depending on the filter type. The BG region was greatly affected by parameter changes in GA but less by those in BW and HA. The error values of the 37 mm insert sphere were 18.0% (BW), 28.2% (GA), and 26.2% (HA), and BW showed the lowest value. CONCLUSION: Our results suggest that the post-reconstruction filtering type used in the 3D-OSEM method was BW from the image quality and quantitative values.

[Investigation of Computed Tomography Exposure Dose for Whole-body 18F-FDG PET/CT Examination in Chugoku-Shikoku Regions].

PURPOSE: We investigated the way of thinking about the CT dose setting, the exposure dose (CTDIvol, DLP) and the image quality (standard deviation of liver: SDliver) of whole-body PET/CT examinations in the Chugoku and Shikoku regions for the optimized CT dose setting. METHOD: It was researched in the target 29 facilities which is equipped with 18F-FDG, PET/CT scanner in that regions. We examined how to determine the dose of complete physical PET/CT setting, the CT radiation dose (CTDIvol and DLP) and the image quality of CT fusion image that is the standard deviation of liver CT value in each facility. RESULT: The optimized CT dose was lower than the diagnostic CT in many facilities. The 75th percentile CTDIvol was 6.01 mGy. The 75th percentile DLP was 560.9 mGy ×cm. The SDliver was 14.6±5.3 HU. CONCLUSION: The CT condition was low setting in comparison with diagnostic CT in many facilities. The exposure dose was lower than the diagnostic CT dose. The image quality of the normal region of liver was very close to the diagnostic CT. Even though it was low dose, images were less noise components.

Effect of Scatter Limitation Correction with Misregistration between Computed Tomography and Positron Emission Tomography on Scatter Correction: A Physical Phantom Study.

PURPOSE: This study aimed to evaluate the advantage of scatter limitation correction with misregistration between µ-map in the computed tomography attenuation correction and positron emission tomography in PET/CT study. METHODS: We used torso phantom including simulated tumor and arms phantom. The CT scan was performed by changing the position of arms phantom after PET scan. Arms phantom movement was out-side direction, in-side direction, and top-side direction by 1-12 cm, respectively. The standardized uptake value (SUV) of simulated tumor and background (B.G.) were evaluated for three specific parameters. Two scatter corrections were performed with scatter correction (SC), and scatter limitation correction (SLC). RESULTS: The SUVmax of simulated tumor was increased by 2.80% (SC), and 2.78% (SLC) on out-side arms movement. In the SUVmax, SC and SLC were decreased by 28.6%, 9.04% on in-side arms, respectively. SUVmax of the SC, and SLC were increased on top-side arms. The scatter fraction factor (SFF) of SC and SLC were 0.25, 0.25 on out-side 5 cm and were 0.732, 0.391 on in-side 5 cm and were 0.785, 0.434 on top-side 12 cm, respectively. CONCLUSION: SLC improved the overestimation of the SUVmax by SC. However, it is necessary to pay attention, in order not to be improved completely. The finding results indicated that SFF was setting 0.40-0.45 in our institute PET/CT system.

[Accuracy of Resolution Recovery in PSF-based Fully-3D PET Image Reconstruction: Simulation and Phantom Study in Multicenter Trial].

PURPOSE: Recently, the quality of positron emission tomography (PET) images has rapidly improved using resolution recovery algorithm with point spread function (PSF). The aim of this study was to investigate the accuracy of the resolution recovery algorithm using three different PET systems. METHODS: Three PET scanner models, the GE Discovery 600 M (D600M), SIEMENS Biograph mCT (mCT), and SHIMADZU SET-3000GCT/X (3000GCT) were used in this study. The radial dependences of spatial resolution (full width at half maximum: FWHM) were obtained by point source measurements (0.9 mmφ). All PET data were acquired in three-dimensional (3D) mode and reconstructed using the filtered back projection (FBP) , 3D-ordered subsets expectation maximization (3D-OSEM or dynamic row-action maximum likelihood algorithm) , and 3D-OSEM+PSF (PSF) algorithms. Two indicators, aspect ratio (ASR) and resolution recovery ratio (RRR), were calculated from measured FWHMs and compared among the three PET scanners. RESULTS: In D600 and 3000GCT, distortions of the radial direction were slightly increased at circumference of field of view (FOV). On the other hand, random distortions were occurred in both radial and tangential direction in mCT. ASRs calculated from 3D-OSEM images at circumference of FOV were 2.06, 1.22, and 2.04 on D600M, mCT, and 3000GCT, respectively. ASR improved with PSF in all PET scanners. On the other hand, RRR with PSF were calculated 57.6%, 61.4%, and 31.6%, respectively. CONCLUSION: Our results suggest that the spatial resolutions of PET images could be improved with PSF algorithm in all PET systems; however, effect of PSF was different depending on PET systems. Furthermore, PSF algorithm could not completely improve spatial resolutions in circumference of FOV.

[Evaluation of Measurement Accuracy and Inter-institutional Comparison for Dose Calibrators].

PURPOSE: The aim of this study was to validate the reliability of dose calibrators for measuring the radioactivity of several radioisotopes in multi-institution. METHODS: We evaluated the measurement accuracy of dose calibrators using a commercially available source ((67) Ga, (99m) Tc, (123) I, (201) TL). Nine dose calibrators (five models) in seven institutions were performed in this study. Each source was measured at least 3 times a day over a period of 4 half-life. Linearity of concentration (%error value) and percent difference values (%diff measurement) between measured and estimated radioactivity were calculated to evaluate the measurement accuracy. In addition, difference among institutions (%diff institution) was evaluated by the error values between measured and reference institution values. RESULTS: Good linearity of concentration was found between measured and estimated radioactivity in (99m)Tc and (123)I. However, %error value was increased in (67)Ga and (201)TL (maximum 19.3%). %diff measurements were 1.9 ± 0.3% for (67)Ga, -0.9 ± 0.3% for (99m)Tc, 2.2 ± 0.4% for (123)I, and -0.7 ± 0.3% for (201)TL, respectively. Although there were no clear differences in six institutions, %diff institution in one institution tended to be higher than that obtained in other institutions. CONCLUSIONS: Our results indicated that measurement accuracy of nine dose calibrators (five models) was relatively stable. However, difference of measured values tended to be higher in a part of institution and source. It is important to perform quality assurance and quality control for dose calibrator using traceable source.

Effects of Non-radioactive Material around Radioactive Material on PET Image Quality.

PURPOSE: Subcutaneous fat is a non-radioactive material surrounding the radioactive material. We developed a phantom, and examined the effect of subcutaneous fat on PET image quality. METHODS: We created a cylindrical nonradioactive mimic of subcutaneous fat, placed it around a cylindrical phantom in up to three layers with each layer having a thickness of 20 mm to reproduce the obesity caused by subcutaneous fat. In the cylindrical phantom, hot spheres and cold spheres were arranged. The radioactivity concentration ratio between the hot spheres and B.G. was 4:1. The radioactivity concentration of B.G. was changed as follows: 1.33, 2.65, 4.00, and 5.30 kBq/mL. 3D-PET images were collected during 10 minutes. RESULTS: When the thickness of the mimicked subcutaneous fat increased from 0 mm to 60 mm, noise equivalent count decreased by 58.9‒60.9% at each radioactivity concentration. On the other hand, the percentage of background variability increased 2.2‒5.2 times. Mimic subcutaneous fat did not decrease the percentage contrast of the hot spheres, and did not affect the cold spheres. CONCLUSION: Subcutaneous fat decreases the noise equivalent count and increases the percentage of background variability, which degrades PET image quality.

[Validation of an optimal analysis method and reproducibility to calculate the heart-to-mediastinum ratio and washout rate in the iodine-123-labeled metaiodobenzylguanidine myocardial scintigraphy].

PURPOSE: The aim of this study was to investigate an appropriate analysis method and multicenter reproducibility of heart-to-mediastinum ratio (H/M) and washout rate (WR) in iodine-123-labeled metaiodobenzylguanidine (123I-MIBG) myocardial scintigraphy with a phantom. METHODS: We evaluated the optimal region of interest (ROI) setting method about the mediastinum and heart by varying the position and shape of the ROI. The mathematical method was changed to a combination of decay time correction (DTC) and background correction (BC). We evaluated the reproducibility of the H/M and WR between institutions. RESULT: H/M decreased to 23.49% and WR increased to 20.68% by changing the mediastinum ROI position from upper to lower. H/M increased to 26.03% by changing the heart ROI position from base to apex. H/M decreased to 38.36% with BC, and WR was reduced up to 48.51% with DTC. Reproducibility of the H/M and WR between institutions was improved by performing optimization of the ROI setting and unification of the mathematical method. DISCUSSION: The position of the mediastinum ROI should be set on the upper mediastinum. The position of the heart ROI should be set on the apex of the heart. WR should be calculated with DTC and BC. Our results suggest that the reproducibility of the H/M and WR between institutions was improved by performing optimization of the ROI setting and unification of the mathematical method.

[Evaluation of potentially influential factors for positron emission tomography image quality in liver signal-to-noise ratio utilizing a delivery ¹8F-fluoro-2-deoxy-D-glucose study on Bi4Ge3O12-positron emission tomography/computed tomography].

UNLABELLED: The purpose of this study was to evaluate the relationship of body habitus, blood glucose level and injected dose, respectively, with BGO (Bi4Ge3O12) positron emission tomography (PET) image quality using commercially available 2-deoxy-2-[¹8F] fluoro-D-glucose (FDG). We also evaluated the relationship between PET image quality and acquisition time for each weight group. METHOD: One hundred twenty-five patients (66 male, 59 female) were enrolled in the study. We adopted liver signal-to-noise ratio (liver SNR) as an image quality index, derived from the region of interest (ROI) placed on the axial image of the liver. RESULTS: The correlation coefficient between liver SNR and dose per weight was 0.502. The liver SNR indicated a negative relationship with body weight, body mass index (BMI) and cross sectional area of the patient's body, with the correlation coefficients of -0.594, -0.479 and -0.522, respectively. For all weight groups, an extended acquisition time of at least 60 s/bed was necessary to improve liver SNR. CONCLUSION: The findings of this study are potentially of use for designing imaging protocols for the BGO-PET/CT system when using commercially available FDG. It is easy to obtain good image quality for patients of low to average body size with the standard injection dose. However, large patients should be injected, wherever possible, with an FDG dose of up to 5 MBq/kg. The acquisition time in overweight and obese patients should be as longer as possible than in standard weight patients.

[Impact of the standardized uptake value on the body trunk with truncation error of µ-map in the positron emission tomography/computed tomography: phantom studies].

PURPOSE: The aim of this study was evaluate to impact of standardized uptake value (SUV) on the body trunk with truncation error of µ-map for CT attenuation correction (CTAC) in whole-body 2-deoxy-2-[(18)F] fluoro-D-glucose ((18)F-FDG)-positron emission tomography (PET)/CT with use of anthropomorphic phantom. METHODS: We used body phantom (2.5 MBq/l) including simulated tumor targets (11.25 MBq/l) and arm phantom. The CT scan was used with a field of view (FOV) of 50 cm. The µ-maps were created by assuming a state of the arm protruding from the FOV (Pmap). A 3D-PET scan with an emission time of 20 min was performed. The PET images were then reconstructed with CTAC, and with and without scatter correction. We evaluated the relationship to Pmap size and the count of simulated tumors and background (B.G.) in PET images which reconstructed the use of each Pmap, respectively. RESULTS: The count of simulated tumor (large) with scatter correction was decreased to 1.3% (Pmap: 15 mm) and 8.8% (Pmap: 35 mm). Then, the count severe reduction was 86.9% in Pmap of 65 mm. The same trend was shown by simulated tumor (middle, small) and B.G. The count of the simulated tumor (large) without scatter correction decreased to 1.3% (Pmap: 15 mm), 6.4% (Pmap: 35 mm) and 13.1% (Pmap: 65 mm). CONCLUSION: Truncation error by µ-map for CTAC in whole-body (18)F-PET/CT caused a decrease of the SUV on the body trunk used for attenuation and scatter correction in the PET images.

[Impact of Residual Radioactivity Rate of 99mTc-macro Aggregated Albumin (MAA) in Syringes and Administration Routes with a Focus on Pediatric Nuclear Medicine Examinations].

PURPOSE: The purpose of this study was to evaluate the residual radioactivity in the syringe and route of administration of a low fluid volume 99mTc-macro aggregated albumin (MAA) intended for pediatric nuclear medicine examinations. METHOD: We evaluated the residual characteristics, as the effect of elapsed time from drawing up of radiopharmaceuticals to plastic syringe to administration, and the effect of volume of 99mTcO4- solution to be labeled, the effect of rinsed times of plastic syringe, effect of dose of calculated by consensus guidelines for pediatric nuclear medicine and residual location in injection sets with 99mTc-MAA. Residual radioactivity was measured using planar images obtained by the gamma camera. RESULTS: Residual radioactivity rate of 99mTc-MAA, 99mTc-MAG3, 123I-IMP showed 41.3±1.6%, 14.4±0.6%, 14.6±2.0%, respectively. 99mTc-MAA clearly showed a higher residual rate. Residual radioactivity rate increased with the extension of the elapsed time, and reached a high value of 41.3% in 30 minutes. Residual radioactivity rate was dependent on the different volume of 99mTcO4- to be labeled (4.0 ml and 8.0 ml). Residual radioactivity rate did not change when the number of rinsed was more than one. Residual rate was around 40% at all doses of calculated by consensus guidelines for pediatric nuclear medicine. CONCLUSION: 99mTc-MAA showed the highest residual radioactivity rate among radiopharmaceuticals used in pediatric nuclear medicine examinations. The factor that most affected the residual radioactivity rate of 99mTc-MAA was the elapsed time from draw up to the plastic syringe to administration.

[Improvement of Standardized Uptake Value Accuracy in the 99mTc Body SPECT and SPECT/CT: Optimization of the Phantom for Calculating Becquerel Calibration Factor and Correction Method].

PURPOSE: The purpose of this study was to evaluate the best phantom for calculating the becquerel calibration factor (BCF) and correction method to obtain the improvement of standardized uptake value (SUV) accuracy in both single photon emission computed tomography (SPECT) and SPECT/CT. METHOD: A SPECT/CT scanner was used in this study. BCFs were calculated using four phantoms with different cross sections including National Electrical Manufacturers Association International Electrotechnical Commission body phantom (NEMA IEC body phantom) filled with 99mTcO4-, and five correction methods were used for reconstruction. SUVs were calculated by the NEMA IEC body phantom and pediatric phantom in house with these BCFs. We then measured SUVmean in the background region of the NEMA IEC body phantom, SUVmax and SUVpeak of the 37-mm-diameter sphere. RESULTS: In the SPECT scanner, SUVmean and SUVmax measured 1.04 and 4.02, respectively, in the case of BCF calculation and SUV measurement using NEMA IEC body phantoms without corrections. In the SPECT/CT scanner, SUVmean with CT attenuation correction (AC) was in agreement with the theoretical values using each phantom. SUVmax showed the same trend. CONCLUSION: In the SPECT scanner, it is possible to obtain a highly accurate SUV by using a phantom that matches the size of the subject for BCF calculation and without correction. In the SPECT/CT scanner, highly accurate SUVs can be obtained by using CT-based attenuation correction, and these values do not depend on the size of the BCF calculation phantom.

Acquisition time optimization of positron emission tomography studies by use of a regression function derived from torso cross-sections and noise-equivalent counts.

In this study, we aimed to optimize the positron emission tomography (PET) acquisition time for individual patients by employing a regression function derived from torso cross-sections by using computed tomography (CT) attenuation corrections and the noise-equivalent counts (NECs). We initially determined the standard image quality or the standard NEC at our institution by visually assessing the images acquired from 61 patients. We measured the NECs of the livers and the torso cross-sections of 165 patients who were evaluated with PET/CT with (18)F-2-fluoro-2-deoxy-D-glucose on the basis of our standard protocol of 120 s/bed position. The optimal acquisition time (OPT) was calculated as the product of the ratio of the standard NEC to the estimated NEC multiplied by 120 s. The estimated NEC was derived from the oval cross-section of each patient by use of the regression function. We evaluated the validity of the OPT equation in 59 additional patients. We determined 5.83 Mcounts as the standard NEC at our institution. The mean OPTs in a group of 59 patients of whom 20, 19, and 20 were underweight, normal-weight, and overweight, respectively, were 106.3 ± 18.0, 137.1 ± 4.6, and 172.1 ± 24.3 s, respectively. After optimization, the NECs for normal-weight and overweight patients increased by 14 and 43 %, respectively, compared with the NECs attained with use of the conventional acquisition time (120 s). Using the regression function based on the torso cross-sections and the NECs enabled optimizations of the PET acquisition times for individual patients.

Differential impact of multi-focus fan beam collimation with L-mode and conventional systems on the accuracy of myocardial perfusion imaging: Quantitative evaluation using phantoms.

OBJECTIVES: A novel IQ-SPECT™ method has become widely used in clinical studies. The present study compares the quality of myocardial perfusion images (MPI) acquired using the IQ-SPECT™ (IQ-mode), conventional (180° apart: C-mode) and L-mode (90° apart: L-mode) systems. We assessed spatial resolution, image reproducibility and quantifiability using various physical phantoms. METHODS: SPECT images were acquired using a dual-headed gamma camera with C-mode, L-mode, and IQ-mode acquisition systems from line source, pai and cardiac phantoms containing solutions of (99m)Tc. The line source phantom was placed in the center of the orbit and at ± 4.0, ± 8.0, ± 12.0, ± 16.0 and ± 20.0 cm off center. We examined quantifiability using the pai phantom comprising six chambers containing 0.0, 0.016, 0.03, 0.045, 0.062, and 0.074 MBq/mL of 99m-Tc and cross-calibrating the SPECT counts. Image resolution and reproducibility were quantified as myocardial wall thickness (MWT) and %uptake using polar maps. RESULTS: The full width at half maximum (FWHM) of the IQ-mode in the center was increased by 11% as compared with C-mode, and FWHM in the periphery was increased 41% compared with FWHM at the center. Calibrated SPECT counts were essentially the same when quantified using IQ-and C-modes. IQ-SPECT images of MWT were significantly improved (P<0.001) over L-mode, and C-mode SPECT imaging with IQ-mode became increasingly inhomogeneous, both visually and quantitatively (C-mode vs. L-mode, ns; C-mode vs. IQ-mode, P<0.05). CONCLUSION: Myocardial perfusion images acquired by IQ-SPECT were comparable to those acquired by conventional and L-mode SPECT, but with significantly improved resolution and quality. Our results suggest that IQ-SPECT is the optimal technology for myocardial perfusion SPECT imaging.

Evaluation of a novel normal database with matched SPECT systems and optimal pre-filter parameters for 3D-SSP.

PURPOSE: A normal perfusion database (NDB) is imperative for the statistical imaging of brain function. This study validates a novel NDB created under the same injection dose and acquisition conditions for three gamma camera systems and evaluates optimal pre-filter parameters for three-dimensional stereotactic surface projections (3D-SSPs). METHOD: We compared a novel NDB that matched the databases in each of three vendor gamma camera systems with a conventionally constructed NDB (conventional NDB) and a NDB constructed in-house for 3D-SSP. We generated hypoperfused regions where pre-specified volumes were simulated for various areas in SPECT images. The properties of each NDB were evaluated based on the distribution of the standard deviation (SD). Abnormal accumulation regions were validated using Z, extent, and artifactual scores. Detection error was used to evaluate the optimal Butterworth pre-filter cutoff frequency with the perfusion defect rate (PDR) in 3D-SSP. RESULTS: The SD distribution was the same in the novel NDB and in the NDB constructed in-house, and the SD of the peak distribution was 0.08-0.07. The Z and extent scores of the novel DB and the NDB constructed in-house were similar, but increased along with the artifactual scores when using the conventional NDB. Many artifacts appeared in the Z score map when using the conventional NDB. The detection error deviated from the actual value by -1.3% at a cutoff frequency of 0.58 cycles/cm and a PDR of 30%, which was the lowest. The cutoff frequency became lower or higher, and the low-perfusion defect rate increased according to the increasing detection error. The optimal cutoff frequency was between 0.52 and 0.58 cycles/cm. CONCLUSIONS: We generated a novel NDB according to the individual devices and compared it with a conventional and a NDB constructed in-house. The Z and extent scores were essentially equal when using the novel DB and the NDB constructed in-house, but considerably differed when using the conventional NDB. The optimal cutoff frequency of the Butterworth filter evaluated from the detection error was in the range of 0.52-0.58 cycles/cm. The detection error increased the perfusion defect rate by <15% and this was undetectable in 3D-SSP. The next step will be to improve the accuracy of the extent of abnormal regions and the sensitivity of the Z score using a novel NDB constructed according to the individual devices.

[Basic evaluation of sampling step angle and spatial resolution in continuous rotating acquisition with SPECT].

In the data sampling in single photon emission computed tomography (SPECT), the continuous rotating acquisition method has high clinical utility. There have been various reports about the optimum sampling step angle for continuous rotating acquisition. Objective evaluation was performed visually and by measuring spatial resolution with a column phantom to find the optimum sampling step angle for continuous rotating acquisition. In locations far from the rotation center, a large sampling step angle produced artificial images with tangential elongation. The spatial resolution was 11.58 ± 0.19 mm full width half maximum (FWHM) as measured at a sampling step angle of 3 degrees and at 10 cm away from the rotation center. Increasing the sampling step angle to more than 3 degrees resulted in an increase of FWHM in the tangential direction. The optimum sampling step angle for continuous rotating acquisition in SPECT needs to be below that calculated from the sampling theorem.