Without physical corrections impacts the performance of myocardial blood flow quantitation with multi-pinhole CZT-SPECT / 中华核医学与分子影像杂志

Objective To investigate the impact on myocardial blood flow (MBF) quantitation with multi-pinhole cadmium zinc telluride (CZT)-SPECT with or without partial physical corrections. Methods A total of 30 patients (18 males, 12 females; age: (63±9) years) with suspected or known coronary heart diseases who underwent dynamic SPECT from July 2018 to January 2019 in Fuwai Hospital were enrolled. Images were reconstructed using different corrections: no correction (NC), partial corrections ((noise re-duction ( NR) , NR+scatter correction ( SC) , NR+SC+resolution recovery ( RR) ) , NR+SC+RR+attenua-tion correction ( AC;total corrections, TC) . Kinetic modeling integrated one-tissue two-compartment model while using index of fitting quality ( R2 ) and fraction blood volume ( FBV) to assess the quality of modeling. Rest MBF ( RMBF) , stress MBF ( SMBF) and myocardial flow reserve ( MFR) quantified from no correc-tion ( NC) or partial corrections were compared with those of TC. Wilcoxon signed rank test and linear re-gression analysis were used to analyze the data. Results Compared to TC, NC showed the lowest R2( rest:0.69, stress:0.78;z values:4.78 and 4.78, both P<0.01) and highest FBV ( rest:0.37, stress:0.40;z values: -3.40 and -3.30, both P<0.01). The improvement of R2 and FBV was consistent with increased corrective terms. Compared with TC, NC overestimated SMBF and MFR ( z values:1.27 and-3.50, both P<0.01), all partial corrections overestimated RMBF and SBMF (z values:from -4.55 to 1.27, all P<0.01). NR and NR+SC underestimated MFR (both P<0.05). Linear regression analysis showed that the regressive coefficients of RMBF between NC, NR, NR+SC, NR+SC+RR and TC were 0.908-1.210, and Bland-Altman plots of RMBF demonstrated positive or negative biases (-0.07, 0.21, 0.26, 0.15 ml·min-1·g-1). The regression coefficients of SMBF were 1. 129-1. 308, and Bland-Altman plots demonstrated positive biases (0. 60, 0.25, 0.28, 0.24 ml·min-1·g-1). The regression coefficients of MFR were 0.907-1.318, and Bland-Altman plots demonstrated positive or negative biases (0.70,-0.11,-0.05, 0.01). Conclusion Full physical corrections can improve the index of fitting quality in the kinetic modeling and reduce left ventricle spillover, which help to warrant the accuracy of SPECT myocardial blood flow quantitation with multi-pin-hole CZR-SPECT.

Without physical corrections impacts the performance of myocardial blood flow quantitation with multi-pinhole CZT-SPECT / 中华核医学与分子影像杂志

Objective@#To investigate the impact on myocardial blood flow (MBF) quantitation with multi-pinhole cadmium zinc telluride (CZT)-SPECT with or without partial physical corrections.@*Methods@#A total of 30 patients (18 males, 12 females; age: (63±9) years) with suspected or known coronary heart diseases who underwent dynamic SPECT from July 2018 to January 2019 in Fuwai Hospital were enrolled. Images were reconstructed using different corrections: no correction (NC), partial corrections ((noise reduction (NR), NR+ scatter correction (SC), NR+ SC+ resolution recovery (RR)), NR+ SC+ RR+ attenuation correction (AC; total corrections, TC). Kinetic modeling integrated one-tissue two-compartment model while using index of fitting quality (R2) and fraction blood volume (FBV) to assess the quality of modeling. Rest MBF (RMBF), stress MBF (SMBF) and myocardial flow reserve (MFR) quantified from no correction (NC) or partial corrections were compared with those of TC. Wilcoxon signed rank test and linear regression analysis were used to analyze the data.@*Results@#Compared to TC, NC showed the lowest R2 (rest: 0.69, stress: 0.78; z values: 4.78 and 4.78, both P<0.01) and highest FBV (rest: 0.37, stress: 0.40; z values: -3.40 and -3.30, both P<0.01). The improvement of R2 and FBV was consistent with increased corrective terms. Compared with TC, NC overestimated SMBF and MFR (z values: 1.27 and -3.50, both P<0.01), all partial corrections overestimated RMBF and SBMF (z values: from -4.55 to 1.27, all P<0.01). NR and NR+ SC underestimated MFR (both P<0.05). Linear regression analysis showed that the regressive coefficients of RMBF between NC, NR, NR+ SC, NR+ SC+ RR and TC were 0.908-1.210, and Bland-Altman plots of RMBF demonstrated positive or negative biases (-0.07, 0.21, 0.26, 0.15 ml·min-1·g-1). The regression coefficients of SMBF were 1.129-1.308, and Bland-Altman plots demonstrated positive biases (0.60, 0.25, 0.28, 0.24 ml·min-1·g-1). The regression coefficients of MFR were 0.907-1.318, and Bland-Altman plots demonstrated positive or negative biases (0.70, -0.11, -0.05, 0.01).@*Conclusion@#Full physical corrections can improve the index of fitting quality in the kinetic modeling and reduce left ventricle spillover, which help to warrant the accuracy of SPECT myocardial blood flow quantitation with multi-pinhole CZR-SPECT.

Potential Clinical Applications of ¹⁸F-Fluorodeoxyglucose Positron Emission Tomography/Magnetic Resonance Mammography in Breast Cancer / 대한핵의학회잡지

The whole-body positron emission tomography (PET)/magnetic resonance (MR) scan is a cutting edge technology providing comprehensive structural information from MR imaging and functional features from PET in a single session. Recent research findings and clinical experience have shown that ¹⁸F-fluorodeoxyglucose (FDG) whole-body PET/MRimaging has a diagnostic performance comparable with or superior to that of PET/CT in the field of oncology, including for breast cancer. In particular, FDG PET/MR mammography in the prone position with the breast hanging in a pendant manner can provide more comprehensive information about the metabolism, anatomy, and functional features of a breast lesion than a whole-body PET/MR scan. This article reports on current state-of-the-art PET/MR mammography in patients with breast cancer and the prospects for potential application in the future.

Impact of Smart Neuro Attenuation Correlation on the Quality and Standardized Uptake Value of Brain PET Imaging / 中国医学影像学杂志

PurposeSmart neuro attenuation correlation (SNAC) is a new method of calculated attention correction. This paper aims to evaluate the impact of SNAC on the quality and standardized uptake value of brain imaging with PET/CT.Materials and Methods Fifty-eight patients who underwent systematic scan with18F-FDG PET/CT were analyzed retrospectively. CT attenuation correlation (CTAC) and SNAC brain PET images were reconstructed respectively. All images were analyzed by visual assessment and Scenium software and the results of the two methods were compared with regard to image contrast, homogeneity and mean SUV at different cerebral regions. Moreover, the correlation of the mean SUV of the two methods was further analyzed.Results There was no significant visual difference of contrast and uniformity between SNAC and CTAC. The Scenium analysis shows that the contrast of SNAC images were slightly higher than that of CTAC, but the difference were not statistically significant (4.19±1.11vs. 4.08±1.03,t=0.764,P>0.05). The uniformity of SNAC images were slightly lower than that of CTAC (1.00vs. 0.83). The mean SUV at various brain regions measured by SNAC was greater than that by CTAC, but both were significantly correlated (r=0.978,P<0.01), and the linear regression analysis also demonstrated that the results were consistent (R2=0.959). Compared with that measured by CTAC, the average percentage difference of SUV measured by SNAC was 8.45±4.71, but it varied greatly at 10 brain regions (-8.56-27.93). The analysis of variance presented significant differences in the average percentage difference of SUV at different brain regions (F=119.084,P<0.01), while the average percentage difference at the outer slices was greater than that at the central slices. Conclusion No significant difference exists in image quality between SNAC and CTAC. Although the mean SUV at different brain regions measured by SNAC may increase by various degrees, it is significantly associated with the results measured by CTAC. Moreover, SNAC simplifies the process of examination and reduces radiation dose, which is beneficial to patients as a qualitative method.

Impact of misregistration between SPECT and CT on attenuation correction of myocardial perfusion imaging / 中华核医学与分子影像杂志

Objective To evaluate the effects of misregistration with different directions and magnitudes between SPECT and CT on image quality and semi-quantification of MPI.Methods The data of 19 healthy volunteers (11 males,8 females ; mean age:(65.3 ± 9.6) years) were retrospectively analyzed.They all had a low pretest likelihood of coronary artery disease according to exercise and rest 99Tcm-MIBI MPI.The CT attenuation correction (CTAC) was performed on a SPECT/CT system.The CT images were manually shifted by 0.5,1.0,1.5,2.0,2.5,3.0,3.5,4.0,4.5 cm distance along the up/down,left/ right,and anterior/posterior axes respectively by using the system built-in software.The counts of the left ventricle were measured using myocardial Bull's eye generated from the reconstructed CTAC images.The image quality and semi-quantification of the CTAC images reconstructed from the raw data with and without shifting were compared and analyzed.Paired t test was used to analyze the data.Results There was no visible artifact with 0.5 cm shifting.The image quality was deteriorated significantly and the counting difference was significant with shifting distance greater than or equal to 1.0 cm.The image artifact of apex wall was mainly due to the upward shift,anterior and apex wall due to the downward shift,septal wall due to the leftward shift,anterior,apex and lateral wall due to the rightward shift,lateral and infero-posterior wall due to the forward shift,anterior,apex and septal wall due to backward shift.The counting difference caused by the downward shift was significantly more severe than that caused by the upward shift ((-9.68±8.06) ％ and (-2.04±1.83)％,t=6.573,P＜0.01) ; and the rightward shift was more severe than the leftward shift ((-9.02± 8.47) ％ and (-4.38±3.67) ％ ; t =1.987,P＜0.05).The image artifacts in anterior,apex and lateral walls were more severe than those in the infero-posterior and septal walls.Conclusions CTAC image artifacts in myocardial perfusion SPECT/CT studies could be caused by misregistration ≥ 1.0 cm.Different directions and magnitudes of shift could result in different degrees of attenuation artifacts at different locations on the original images.

The influence of integrated-CT artifacts on the attenuation correction results of SPECT/CT bone imaging / 中国医学影像技术

Objective To evaluate the influence of integrated-CT artifacts on attenuation-corrected (AC) images of SPECT bone imaging. Methods Imaging documents of 78 patients who underwent SPECT/CT bone imaging were retrospectively analyzed, and the artifacts on CT images and CT attenuation maps were visually studied. Compared with the non-attenuation corrected (NC) images, the coefficient of variation (CV) and percentage difference (PD) of radioactive count of regional bone influenced by CT artifacts were calculated and statistically analyzed to estimate the influence of CT artifacts on AC images of SPECT bone imaging. Results The integrated-CT artifacts were found in 38 patients of 78, and appeared the same image findings as those on CT attenuation maps respectively, including truncation artifact, thoraco-abdominal gas artifact, photon starvation artifact, etc. On all the AC images with integrated-CT artifacts, regional bones were influenced not only on uniformity (CVAC 17.62%±4.13%, CVNC 11.19%±3.81%;t=2.13, P<0.05), but also by the distribution (PDAC 16.98%±3.31%, PDNC 9.84%±1.62%;t=2.46, P<0.05) of radioactive count. Conclusion Artifacts on integrated-CT images can induce false AC information on CT attenuation maps, therefore, a comparative analysis with NC images is recommended if necessary.

Whole Body Imaging Using 18-Fluorine Fluorodeoxyglucose (18F-FDG) Positron Emission Tomography/Computed Tomography (PET/CT) with or without Contrast Enhanced Computed Tomography (CT) in Dignosing Arteritis

Introduction: Takayasu's Arteritis and Horton's Arteritis are two rare cases of auto-immune complex diseases resulting in sterile inflammatory reactions affecting the wall of large and medium sized arteries. Various radiological and interventional methods employed are inconclusive and become diagnostic only when complications begin to set in. The new non-invasive hybrid Positron Emission Tomography Computed Tomography (PET/CT) using 18Florine-Fluorodeoxyglucose (18F-FDG) imaging technique could detect arteritis in an early clinical stage when routine conventional cross-sectional imaging was inconclusive. Method: Two cases from Klagenfurt Hospital, Austria and Milan General Hospital, Italy were compared with image acquisition being done in the respective hospitals. In Klagenfurt, PET/CT image acquisition was performed using intravenous contrast administration and in Milan, CT parameters were used as attenuation correction and anatomical correlation of PET images. Results: CT performed using both methods, with or without iodinated contrast media, were useful in detecting arteritis. Conclusion: It is concluded that PET/CT aside from being a useful tool in cancer imaging, is also useful for pyrexia of unknown origin. PET/CT should be employed early in managing this clinical condition where arteritis is a possible diagnosis.

Physical Artifact Correction in Nuclear Medicine Imaging: Normalization and Attenuation Correction / 핵의학분자영상

Artifact corrections including normalization and attenuation correction were important for quantitative analysis in Nuclear Medicine Imaging. Normalization is the process of ensuring that all lines of response joining detectors in coincidence have the same effective sensitivity. Failure to account for variations in LOR sensitivity leads to bias and high-frequency artifacts in the reconstructed images. Attenuation correction is the process of the correction of attenuation phenomenon lies in the natural property that photons emitted by the radiopharmaceutical will interact with tissue and other materials as they pass through the body. In this paper, we will review the several approaches for normalization and attenuation correction strategies.

Motion Correction in PET/CT Images / 핵의학분자영상

PET/CT fused image with anatomical and functional information have improved medical diagnosis and interpretation. This fusion has resulted in more precise localization and characterization of sites of radio-tracer uptake. However, a motion during whole-body imaging has been recognized as a source of image quality degradation and reduced the quantitative accuracy of PET/CT study. The respiratory motion problem is more challenging in combined PET/CT imaging. In combined PET/CT, CT is used to localize tumors and to correct for attenuation in the PET images. An accurate spatial registration of PET and CT image sets is a prerequisite for accurate diagnosis and SUV measurement. Correcting for the spatial mismatch caused by motion represents a particular challenge for the requisite registration accuracy as a result of differences in PET/CT image. This paper provides a brief summary of the materials and methods involved in multiple investigations of the correction for respiratory motion in PET/CT imaging, with the goal of improving image quality and quantitative accuracy.

Quantitative Comparisons between CT and 68Ge Transmission Attenuation Corrected 18F-FDG PET Images: Measured Attenuation Correction vs. Segmented Attenuation Correction / 핵의학분자영상

PURPOSE: It was reported that CT-based measured attenuation correction (CT-MAC) produced radioactivity concentration values significantly higher than 68Ge-based segmented attenuation correction (Ge-SAC) in PET images. However, it was unknown whether the radioactivity concentration difference resulted from different sources (CT vs. Ge) or types (MAC vs. SAC) of attenuation correction (AC). We evaluated the influences of the source and type of AC on the radioactivity concentration differences between reconstructed PET images in normal subjects and patients. MATERIAL AND METHODS: Five normal subjects and 35 patients with a known or suspected cancer underwent 18F-FDG PET/CT. In each subject, attenuation corrected PET images using OSEM algorithm (28 subsets, 2 iterations) were reconstructed by 4 methods: CT-MAC, CT-SAC, Ge-MAC, and Ge-SAC. The physiological uptake in normal subjects and pathological uptake in patients were quantitatively compared between the PET images according to the source and type of AC. RESULTS: The SUVs of physiological uptake measured in CT-MAC PET images were significantly higher than other 3 differently corrected PET images. Maximum SUVs of the 145 foci with abnormal FDG uptake in CT-MAC images were significantly highest among 4 differently corrected PET images with a difference of 2.4% to 5.1% (p<0.001). The SUVs of pathological uptake in Ge-MAC images were significantly higher than those in CT-SAC and Ge-MAC PET images (p<0.001). CONCLUSION: Quantitative radioactivity values were highest in CT-MAC PET images. The adoption of MAC may make a more contribution than the adoption of CT attenuation map to such differences.

The Effect of Intravenous Contrast on SUV Value in 18F-FDG PET/CT using Diagnostic High Energy CT / 핵의학분자영상

PURPOSE: According to the development of CT scanner in PET/CT system, the role of CT unit as a diagnostic tool has been more important. To improve the diagnostic ability of CT scanner, it is a key aspect that CT scanning has to be performed with high dose energy and intravenous (IV) contrast. So we investigated the effect of IV contrast media on the maximum SUV (maxSUV) of normal tissues and pathologic lesions using PET/CT scanner with high dose CT scanning. MATERIALS AND METHODS: The study enrolled 13 patients who required PET/CT evaluation. At first, the patients were performed whole body non-contrast CT (NCCT - 120 kVp, 130 mAs) scan. Then contrast enhanced CT (CECT) scan was performed immediately. Finally PET scan was followed. The PET emission data were reconstructed twice, once with the NCCT and again with the CECT. We measured the maxSUV of 10 different body regions that were considered as normal in all patients. Also pathologic lesions were investigated. RESULTS: There were not seen focal artifacts in PET images based on CT with IV contrast agent. Firstly, 130 normal regions in 13 patients were evaluated. The maxSUV was significantly different between two PET images (p<0.001). The maxSUV was 1.1+/-0.5 in PET images with CECT-corrected attenuation and 1.0+/-0.5 in PET images with NCCT-corrected attenuation. The limit of agreement was 0.1+/-0.3 in Bland-Altman analysis. Especially there were significant differences in 6 of 10 regions, apex and base of the right lung, ascending aorta, segment 6 and segment 8 of the liver and spleen (p<0.05). Secondly, 39 pathologic lesions were evaluated. The maxSUV was significantly different between two PET images (p<0.001). The maxSUV was 4.7+/-2.0 in PET images with CECT-corrected attenuation and 4.4+/-2.0 in PET images with NCCT-corrected attenuation. The limit of agreement was 0.4+/-0.8 in Bland-Altman analysis. CONCLUSION: Although there were increases of maxSUVs in the PET images based on CT with IV contrast agent, it was very narrow in the range of limit of agreement. So there was no significant effect to clinical interpretation for PET images that were corrected attenuation with high dose CT using IV contrast.

Effects of Attenuation and Scatter Corrections in Cat Brain PET Images Using microPET R4 Scanner / 핵의학분자영상

PURPOSE: The aim of this study was to examine the effects of attenuation correction (AC) and scatter correction (SC) on the quantification of PET count rates. MATERIALS AND METHODS: To assess the effects of AC and SC, 18F-FDG PET images of phantom and cat brain were acquired using microPET R4 scanner. Thirty-minute transmission images using 68Ge source and emission images after injection of FDG were acquired. PET images were reconstructed using 2D OSEM. AC and SC were applied. Regional count rates were measured using ROIs drawn on cerebral cortex including frontal, parietal, and latral temporal lobes and deep gray matter including head of caudate nucleus, putamen and thalamus for pre- and post-AC and SC images. The count rates were then normalized with the injected dose per body weight. To assess the effects of AC, count ratio of "deep gray matter/cerebral cortex" was calculated. To assess the effects of SC, ROIs were also drawn on the gray matter (GM) and white matter (WM), and contrast between them ((GM-WM)/GM) was measured. RESULTS: After the AC, count ratio of "deep gray matter/cerebral cortex" was increased by 17+/-7%. After the SC, contrast was also increased by 12+/-3%. CONCLUSION: Relative count of deep gray matter and contrast between gray and white matters were increased after AC and SC, suggesting that the AC would be critical for the quantitative analysis of cat brain PET data.

Impact of Contrast Agent for PET Images with CT-based Attenuation Correction / 의학물리

Experiments and simulation were done to study the impact of contrast agent when CT scan was used to attenuation correction for PET images in PET/CT system. Whole body phantom was imaged with various concentration of iodine-based contrast agent using CT. Mathematical emission and transmission density map with liver were made to simulate for whole body FDG imaging. A variety of factors were estimated, including non-uniform enhancement of contrast agent, concentration and distribution size of contrast agent, noise level, image resolution, reconstruction algorithm, hypo-attenuation of contrast agent, and different time phases for contrast agent. Experimental studies showed that Hounsfield unit depends on the concentration of contrast agent and tube voltage. From the simulation data, contrast agents introduced artifacts and degraded image quality on the attenuation-corrected PET images. The severity of these effects depends on a variety of factors, including the concentration and distribution size of contrast agent, the noise levels, and the image resolution. These results indicated that the impact of contrast agents should be considered with a full understanding of their potential problems in clinical PET/CT images.

The Effect of Attenuation Correction with CT on the Interpretation of Myocardial Perfusion SPECT: in Patients with Normal Coronary Angiogram / 대한핵의학회잡지

PURPOSE: There has been many reports for the effect of attenuation correction on myocardial perfusion SPECT. We studied the effect of attenuation correction with CT (computed tomography) in patients with normal coronary angiography. MATERIALS AND METHODS: Fifteen patients with normal coronary artery on angiography and low likelihood of coronary artery disease were enrolled in this study (male: 6, female: 9, mean age: 58+/-8 year). Myocardial perfusion SPECT was done with Millennium VG with Hawkeye device (GE, SPECT/CT camera). A visual analysis and polar map quantification (Emory tool box) was performed. In quantitative analysis, percent uptake of each myocardial wall on polar map (percent of maximal uptake) was compared between non-corrected (NC) and corrected (AC) images. RESULTS: Visual analysis showed AC images led to an increase of uptake in the inferior wall, but decrease of uptake in the anterior wall, apex and septum. Liver activity is also increased in AC images. In quantitative analysis, the percent uptake is decreased in the anterior wall, apex and septum, but increased in the inferior wall. It is helpful to interpret the images in the inferior wall after AC, but difficult in the apex and anterior wall after AC. CONCLUSION: AC is helpful in the inferior wall. But in the apex or anterior wall, AC must be carefully applied to normal perfused myocardium.

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.

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.

PET-CT: a functional imaging device / 医疗卫生装备

PET-CT is a functional imaging device with a complicated imaging theory and technique. It attracts some arguments when applied clinically. This paper discusses mainly its technique problems and its prospects in the future.

Improved Activity Estimation using Combined Scatter and Attenuation Correction in SPECT / 대한핵의학회잡지

PURPOSE: The pvrpose of this study was to evaluate the accuracy of radioactivity quantitation in Tc-99m SPECT by using combined scatter and attenuation correction. MATERIALS AND METHODS: A cylindrical phantom which simulates tumors (T) and normal tissue (B) was filled with varying activity ratios of Tc-99m. We acquired emission scans of the phantom using a three-headed SPECT system (Trionix, Inc.) witb two energy windows (photopeak window: 126 154 keV and scatter window: 101 123 keV). We performed the scatter correction with dual-energy window subtraction method (k=0.4) and Chang attenuation correction. Three sets of SPECT images were reconstructed using combined scatter and attenuation correction (SC+AC', attenuation correction (AC) and without any correction (NONE). We compared T/B ratio, irnage contrast [(T-B)/(T+B)) and absolute radioactivity with true values. RESULTS: SC+AC images had the highest mean values of T/B ratios. Image contrast was 0.92 in SC+AC, which was close to the true value of 1, and higher than AC (0.77) or NONE (0.80). Errors of true activity by SPECT images ranged from 1 to 11% for SC+AC, 22-47% for AC, and 2 16% for NONE in a phantom which was located 2.4cm from the phantom surface. In a phantom located 10,0cm from the surface, SC+AC underestimated by ?4%, NON.E 40%. However, AC overestimated by 10%. CONCLUSION: We conclude that accurate SPECT activity quantitation of Tc-99m distribution can be achieved by dual window scatter correc.tion combined with attenuation correction.