Assessment of Attenuation Correction Techniques with a 137Cs Point Source / 대한핵의학회잡지

PURPOSE: The objective of this study was to assess attenuation correction algorithms with the 137Cs point source for the brain positron emission tomography (PET) imaging process. MATERIALS AND METHODS: Four different types of phantoms were used in this study for testing various types of the attenuation correction techniques. Transmission data of a 137Cs point source were acquired after infusing the emission source into phantoms and then the emission data were subsequently acquired in 3D acquisition mode. Scatter corrections were performed with a background tail-fitting algorithm. Emission data were then reconstructed using iterative reconstruction method with a measured (MAC), elliptical (ELAC), segmented (SAC) and remapping (RAC) attenuation correction, respectively. Reconstructed images were then both qualitatively and quantitatively assessed. In addition, reconstructed images of a normal subject were assessed by nuclear medicine physicians. Subtracted images were also compared. RESULTS: ELAC, SAC, and RAC provided a uniform phantom image with less noise for a cylindrical phantom. In contrast, a decrease in intensity at the central portion of the attenuation map was noticed at the result of the MAC. Reconstructed images of Jaszack and Hoffan phantoms presented better quality with RAC and SAC. The attenuation of a skull on images of the normal subject was clearly noticed and the attenuation correction without considering the attenuation of the skull resulted in artificial defects on images of the brain. CONCLUSION: the complicated and improved attenuation correction methods were needed to obtain the better accuracy of the quantitative brain PET images.

Improved Scatter Correction for SPECT Images: A Monte Carlo Simulation Study / 대한핵의학회잡지

PURPOSE: Abutted scatter energy windows used for a triple energy window (TEW) method may provide wrong estimation of scatter. This study is to propose an extended TEW (ETEW) method, which doesn't require abutted scatter energy windows and overcomes the shortcomings of TEW method. MATERIALS AND METHODS: The ETEW is a modification of the TEW which corrects for scatter by using abutted scatter rejection windows, which can overestimate or underestimate scatter. The ETEW is compared to the TEW using Monte Carlo simulated data for point sources as well as hot and cold spheres in a cylindrical water phantom. Various main energy window widths (10 %, 15 % and 20 %) were simulated. Both TEW and ETEW improved image contrast, % recovery coefficients and normalized standard deviation. RESULTS: Both of TEW and ETEW improved image contrast and % recovery coefficients. Estimated scatter components by the TEW were not proportional to the true scatter components over the main energy windows when ones of 10 %, 15 %, and 20 % were simulated. The ETEW linearly estimated scatter components over the width of the main energy windows. CONCLUSION: We extended the TEW method into the method which could linearly estimate scatter components over the main energy windows.

Evaluation of a Conjugate View Method for Determination of Kidney Uptake / 대한핵의학회잡지

PURPOSE: In order to obtain better quantitation of kidney uptake, this study is to evaluate a conjugate view method (CVM) using a geometric mean attenuation correction for kidney uptake and to compare it to Gate's method. MATERIALS AND METHODS: We used a Monte Carlo code, SIMIND and a Zubal phantom, to simulate kidney uptake. SIMIND was both simulated with or without scatter for the Zubal phantom. Also, a real phantom test was carried out using a dual-head gamma camera. The activity of 0.5 mCi was infused into two small cylinder phantoms of 5 cm diameter, and then, they were inserted into a cylinder phantom of 20 cm diameter. The results by the CVM method were compared with ideal data without both of attenuation and scatter and with Gate's method. The CVM was performed with or without scatter correction. The Gate's method was performed without scatter correction and it was evaluated with regards to 0.12 cm (-1) and 0.15 cm (-1) attenuation coefficients. Data were analyzed with comparisons of mean counts in the regions of interest (ROI), profiles drawn over kidney images and linear regression. Correlation coefficients were calculated with ideal data, as well. RESULTS: In the case of the computer simulation, mean counts measured from ideal data, the CVM and the Gate's method were (right: 998 +/- 209, left: 896 +/- 249), (right: 911 +/- 207, left: 815 +/- 265), and (right: 1065 +/- 267, left: 1546 +/- 267), respectively. The ideal data showed good correlation with the CVM and the correlation coefficients of the CVM, Gate's method were (right: 0.91, left: 0.93) and (right: 0.85, left: 0.90), respectively. CONCLUSION: The conjugate view method using geometric mean attenuation correction resulted in better accuracy than the Gate's method. In conclusion, the conjugate view method independent of renal depths may provide more accurate kidney uptake.

Increase of Tc-99m RBC SPECT Sensitivity for Small Liver Hemangioma using Ordered Subset Expectation Maximization Technique / 대한핵의학회잡지

No abstract available.

Increase of Tc-99m RBC SPECT Sensitivity for Small Liver Hemangioma using Ordered Subset Expectation Maximization Technique / 대한핵의학회잡지

No abstract available.

Standard Performance Measurements of GE AdvanceTM Positron Emission Tomography / 대한핵의학회잡지

PURPOSE: The purpose of this study was to establish optimal imaging acquisition conditions for the GE Advance(TM) PET imaging system by performing the acceptance tests designed by National Electrical Manufacturers Association (NEMA) protocol and General Electric Medical Systems (GEMS) test procedures. MATERIALS AND METHODS: Performance tests were carried out with 18FDG radioactivity source and phantoms by using a standard acquisition mode. Transaxial resolution and scatter fraction tests were performed with a line source and axial resolution with a point source, respectively. A cylindrical phantom made of polymethylmethacrylate (PMMA) was used to measure sensitivity, count rate losses and randoms, uniformity correction, and attenuation inserts were added to measure remaining tests. The test results were acquired in a diagnostic acquisition mode and analyzed mainly on high sensitivity mode. RESULTS: Transaxial resolution and axial resolution were measured as average of 4.65 mm and 3.98 mm at 0 cm, and 6.02 mm and 6.71 mm at 20 cm on high sensitivity mode, respectively. Average scatter fraction was 9.87%, and sensitivity was 225.8 kcps/micronCi/cc of trues. Activity at 50% deadtime was 4.6 Ci/cc, and the error of count rate correction at that activity was from 1.49% to 3.83%. Average nonuniformity for total slice was 8.37%. The accuracy of scatter correction was -0.95%. The accuracies of attenuation correction were 5.68% for air, 0.04% for water and -6.51% for polytetrafluoroethylene (PTFE). CONCLUSION: The results satisfied most acceptance criteria, indicating that the GE AdvanceTM PET system can be optimally used for clinical applications.

Development and Performance Test of Preamplifier and Amplifier for Gamma Probe / 대한핵의학회잡지

PURPOSE: Preamplifier and amplifier are very important parts for developing a portable counting or imaging gamma probe. They can be used for analyzing pulses containing energy and position information for the emitted radiations. The commercial Nuclear Instrument Modules (NIMs) can be used for processing these pulses. However, it may be improper to use NIMs in developing a portable gamma probe, because of its size and high price. The purpose of this study was to develop both preamplifier and amplifier and measure their performance characteristics. MATERIALS and Methodes: The preamplifier and amplifier were designed as a charge sensitive device and a capacitor resistor-rsistor capacitor (CR-RC) electronic circuit, respectively, and they were mounted on a print circuit board (PCB). We acquired and analyzed energy spectra for Tc-99m and Cs-137 using both PCB and NIMs. Multichannel analyzer (Accuspec/A, Caberra Industries Inc., Meriden Connecticut, U.S.A) and scintillation detectors (EP-047 (Bicron Saint-Gobain/Norton Industrial EP-047 (Ceramics Co., Ohio, U.S.A) with 2"x2" NaI (T1) crystal and R1535 (Hamamatsu Photonics K.K., Electron Tube Center, Shizuoka-ken, Japan) with 1"x1"NaI (T1) crystal) were used for acquiring the energy spectra. RESULTS: Using PCB, energy resolutions or EP-047 detectors for Tc-99m and Cs-137 were 12.92% and 5.01%, respectively, whereas R1535 showed 13.75% and 5.19% of energy resolution. Using the NIM devices, energy resolutions of EP-047 detector for Tc-99m and Cs-137 were measured as 14.6% and 7.58%, respectively. However, reliable energy spectrum of R1535 detector could not be acquired, since its photomultiplier tube (PMT) requires a specific type of preamplifier. CONCLUSION: We developed a special preamplifier and amplifier suitable for a small sized gamma probe that showed good energy resolutions independent of PMT types. The RESULTS indicate that the PCB can be used in developing both counting and imaging gamma probe.

Comparison Studies of SPECT Dopamine Transporter Imaging and Noninvasive Quantification using TRODAT-1 and IPT / 대한핵의학회잡지

The SPECT radiopharmaceuticals labeled with I-123 for dopamine transporter imaging have been used to measure dopamine transporters in patients with movement disorders. However, a cyclotron produced I-123 limits its availiability and ease of use as a radioisotope to be labeled with pharmaceuticals in routine clinical diagnostic procedures. Recently, new radiopharmaceuticals for Tc-99m which has optimal characteristic for SPECT imaging have been developed to overcome the limits of using I-123. The purpose of this study was to compare the quality of [Tc-99m]TRODAT-1 with [I-123]IPT SPECT data and then to evaluate the usefulness of [Tc-99m]TRODAT-I SPECT by using three noninvasive simplified quantitative methods. TRODAT-1 labeled with Tc-99m(15.93+/-0.82 mCi) and IPT labeled with I-123(6.60+/-0.11 mCi) were injected into five normal controls. Dynamic [Tc-99m] TRODAT-I SPECT scans of brain were performed for 10 minutes each over 180 minnutes, and for 20 minutes at 4 hrs and 5 hrs. [I-123IPT SPECT scans were performed for 5 minutes each over 120 minutes. Time activity curves were generated for the left basal ganglia(LBG), right basal ganglia(RBG), and occipital cortex(OCC). Dopamine transporter parameters were obtained using (BG-OCC)/OCC, graphical method(Rv), and area ratio method(RA). TRODAT-1 and IPT SPECT imaging showed high uptake at the level of the basal ganglia. (BG-OCC)/OCC ratios for TRODAT-1 and IPT were 0.80+/-0.14, and 3.22+/-0.81, Rvs were 0.62+/-0.12, and 2.30+/-0.35, and RAs were 0.37+/-0.08 and 1.73+/-0.31, respectively. In conclusion, further improvement of [Tc-99m]TRODAT-I imaging characteris- tics may be required to estimate the dopamine transporter concentrations in human brains although it shows clear BG localization.