Value of Patlak Ki images from 18F-FDG-PET/CT for evaluation of the relationships between disease activity and clinical events in cardiac sarcoidosis.

The association between 18F-fluorodeoxyglucose (18F-FDG) myocardial uptake and clinical presentations in cardiac sarcoidosis (CS) has not yet been clarified. The Patlak slope, Ki, which represents the rate of 18F-FDG uptake is a quantitative index of 18F-FDG metabolism. This study aims to investigate the usefulness of standardized uptake value (SUV) and Patlak Ki images (Ki images) extracted from dynamic 18F-FDG-PET/CT for evaluating the risk of clinical events (CEs) in CS. The SUV and Ki myocardial images were generated from 30 dynamic 18F-FDG-PET/CT scans of 21 CS patients. The SUV and Ki images both were rated as positive in 19 scans and negative in 11 scans with the same incidence of CEs which were significantly higher in positive than negative scans [cardiac dysfunction: 78.9% (15/19) vs. 27.2% (3/11); arrhythmic events: 65.5% (10/19) vs. 0% (0/11)]. In 19 positive scans, the three Ki parameters (Ki max, Ki mean and Ki volume) were significantly higher in scans for patients with arrhythmic events than in those without. Logistic regression analysis showed that the Ki volume alone was significantly associated with the risk of arrhythmic events. Our study suggests that Ki images may add value to SUV images for evaluating the risk of CEs in CS patients.

Direct comparison of brain [18F]FDG images acquired by SiPM-based and PMT-based PET/CT: phantom and clinical studies.

BACKGROUND: Silicon photomultiplier-positron emission tomography (SiPM-PET) has better sensitivity, spatial resolution, and timing resolution than photomultiplier tube (PMT)-PET. The present study aimed to clarify the advantages of SiPM-PET in 18F-fluoro-2-deoxy-D-glucose ([18F]FDG) brain imaging in a head-to-head comparison with PMT-PET in phantom and clinical studies. METHODS: Contrast was calculated from images acquired from a Hoffman 3D brain phantom, and image noise and uniformity were calculated from images acquired from a pool phantom using SiPM- and PMT-PET. Sequential PMT-PET and SiPM-PET [18F]FDG images were acquired over a period of 10 min from 22 controls and 10 patients. All images were separately normalized to a standard [18F]FDG PET template, then the mean standardized uptake values (SUVmean) and Z-score were calculated using MIMneuro and CortexID Suite, respectively. RESULTS: Image contrast, image noise, and uniformity in SiPM-PET changed 19.2, 3.5, and - 40.0% from PMT-PET, respectively. These physical indices of both PET scanners satisfied the criteria for acceptable image quality published by the Japanese Society of Nuclear Medicine of contrast > 55%, CV ≤ 15%, and SD ≤ 0.0249, respectively. Contrast was 70.0% for SiPM-PET without TOF and 59.5% for PMT-PET without TOF. The TOF improved contrast by 3.5% in SiPM-PET. The SUVmean using SiPM-PET was significantly higher than PMT-PET and did not correlate with a time delay. Z-scores were also significantly higher in images acquired from SiPM-PET (except for the bilateral posterior cingulate) than PMT-PET because the peak signal that was extracted by the calculation of Z-score in CortexID Suite was increased. The hypometabolic area in statistical maps was reduced and localized using SiPM-PET. The trend was independent of whether the images were derived from controls or patients. CONCLUSIONS: The improved spatial resolution and sensitivity of SiPM-PET contributed to better image contrast and uniformity in brain [18F]FDG images. The SiPM-PET offers better quality and more accurate quantitation of brain PET images. The SUVmean and Z-scores were higher in SiPM-PET than PMT-PET due to improved PVE. [18F]FDG images acquired using SiPM-PET will help to improve diagnostic outcomes based on statistical image analysis because SiPM-PET would localize the distribution of glucose metabolism on Z-score maps.

Effects of the addition of low-dose ketamine to propofol anesthesia in the dental procedure for intellectually disabled patients.

BACKGROUND: This study aimed to examine whether the combination of low-dose ketamine and propofol in deep sedation is clinically useful in controlling the behavior in intellectually disabled patients who are typically extremely noncooperative during dental procedures. METHODS: A total of 107 extremely noncooperative intellectually disabled adult patients were analyzed. In all patients, deep sedation was performed using either propofol alone (group P) or using a combination of propofol and 0.2 mg/kg or 0.4 mg/kg ketamine (groups PK0.2 and PK0.4, respectively). The procedures were performed in the order of insertion of nasal cannula into the nostril, attachment of mouth gag, and mouth cleaning and scaling. The frequency of patient movement during the procedures, mean arterial pressure, heart rate, peripheral oxygen saturation, recovery time, discharge time, and postoperative nausea and vomiting were examined. RESULTS: The three groups were significantly different only in the frequency of patient movement upon stimulation during single intravenous injection of propofol and scaling. CONCLUSION: For propofol deep sedation, in contrast to intravenous injection of propofol alone, prior intravenous injection of low-dose ketamine (0.4 mg/kg) is clinically useful because it neither affects recovery, nor causes side effects and can suppress patient movement and vascular pain during procedures.

Multiple-animal MR imaging using a 3T clinical scanner and multi-channel coil for volumetric analysis in a mouse tumor model.

PURPOSE: Multiple small-animal magnetic resonance (MR) imaging to measure tumor volume may increase the throughput of preclinical cancer research assessing tumor response to novel therapies. We used a clinical scanner and multi-channel coil to evaluate the usefulness of this imaging to assess experimental tumor volume in mice. METHODS: We performed a phantom study to assess 2-dimensional (2D) geometric distortion using 9-cm spherical and 32-cell (8×4 one-cm(2) grids) phantoms using a 3-tesla clinical MR scanner and dedicated multi-channel coil composed of 16 5-cm circular coils. Employing the multi-channel coil, we simultaneously scanned 6 or 8 mice bearing sarcoma 180 tumors. We estimated tumor volume from the sum of the product of tumor area and slice thickness on 2D spin-echo images (repetition time/echo time, 3500/16 ms; in-plane resolution, 0.195×0.195×1 mm(3)). After MR acquisition, we excised and weighed tumors, calculated reference tumor volumes from actual tumor weight assuming a density of 1.05 g/cm(3), and assessed the correlation between the estimated and reference volumes using Pearson's test. RESULTS: Two-dimensional geometric distortion was acceptable below 5% in the 9-cm spherical phantom and in every cell in the 32-cell phantom. We scanned up to 8 mice simultaneously using the multi-channel coil and found 11 tumors larger than 0.1 g in 12 mice. Tumor volumes were 1.04±0.73 estimated by MR imaging and 1.04±0.80 cm(3) by reference volume (average±standard deviation) and highly correlated (correlation coefficient, 0.995; P<0.01, Pearson's test). CONCLUSION: Use of multiple small-animal MR imaging employing a clinical scanner and multi-channel coil enabled accurate assessment of experimental tumor volume in a large number of mice and may facilitate high throughput monitoring of tumor response to therapy in preclinical research.

An anthropomorphic pelvis phantom for optimization of the diagnosis of lymph node metastases in the pelvis.

OBJECTIVE: An anthropomorphic pelvis phantom was made by the modification of a National Electrical Manufacturers Association (NEMA) phantom, currently the most popular one, and its clinical usefulness was evaluated. METHODS: The NEMA plus bone phantom was made by placing the pelvic bone model in the NEMA phantom. The NEMA plus bladder phantom was made by placing an imitation of the urinary bladder in the NEMA phantom. The pelvis phantom was also made by placing both the pelvic bone model and the bladder in the NEMA phantom. Four kinds of phantoms were imaged by both 2D and 3D dynamic modes, and for each phantom, prompt coincidence count rates, random ones, true plus scatter ones, and single photon rates were measured and these coincidence count rates were compared with those from the actual clinical data. After image reconstruction, the contrast ratio and image noise were also investigated. RESULTS: For the random coincidence count rate, the data obtained from each phantom showed good correspondence to the clinical data. The prompt coincidence count rates and true plus scatter ones of the clinical data were different from those obtained from NEMA phantom, NEMA plus bone one and NEMA plus bladder one, whereas there was a good correspondence between the data of the pelvis phantom and the clinical data. For the contrast ratio and image noise, there were discrepancies between the data of NEMA phantom and pelvis phantoms. CONCLUSIONS: We made an anthropomorphic pelvis phantom by the simple modification of a NEMA phantom. This phantom showed performance similar to that of the actual human pelvis, suggesting clinical usefulness in the evaluation of new acquisition protocols and reconstruction algorithms.

Improvement of the diagnostic accuracy of lymph node metastases of colorectal cancer in 18F-FDG-PET/CT by optimizing the iteration number for the image reconstruction.

OBJECTIVE: Improvement in the diagnostic accuracy of lymph node (LN) metastases of colorectal cancer by optimizing the reconstruction parameters was studied, including a phantom study and clinical studies. METHODS: In the experimental study, the contrast ratio was evaluated using a standard image quality phantom, changing the iteration number of ordered subsets expectation maximization algorithm from 2 to 6. In the clinical study, 89 patients with preoperative colorectal cancer who received 18F-2-deoxy-2-fluoro-D: -glucose positron emission tomography/computed tomography (PET/CT) were studied. Their LN metastases were visually assessed when systematically changing the iteration number, and the optimal iteration number was determined. After the appropriate cut-off value of maximum standardized uptake value was determined, the improvement of the diagnostic accuracy of LN metastases was evaluated for the proximal nodes and the distal ones using the reconstructed images with the optimal iteration number. This was compared with the conventional method that had an iteration number of 2. RESULTS: In the phantom study, it was confirmed that the contrast ratio improved when the iteration number increased. In clinical evaluation, the optimal iteration number was determined to be 5 by visual assessment. When the cut-off value of 1.5 was used, which happened to be the best number, the sensitivity/specificity/accuracy improved from 52%/91%/72% to 77%/89%/83% for the proximal nodes, and from 63%/90%/84% to 91%85%/87% for the distal nodes, respectively. CONCLUSIONS: When the iteration number of the reconstruction algorithm was optimized, the sensitivity of LN metastasis improved by more than 20%, and the accuracy exceeded 80%. Optimization of the image reconstruction parameters in the diagnosis of LN metastases using PET/CT is clinically important.

Diagnosis supporting algorithm for lymph node metastases from colorectal carcinoma on 18F-FDG PET/CT.

OBJECTIVE: We studied the improvement of the detect-ability of lymph node (LN) metastases from colorectal cancer in (18)F-fluorodeoxyglucose positron emission tomography (FDG PET)/computed tomography (CT) by analyzing the acquired counts with a statistical method. METHODS: Thirty-nine metastatic LNs from 32 cases with colorectal cancer were included in this study. "Uptake region" was defined as the site where counts were higher than the average plus 3 standard deviations (SDs) on each transaxial image of FDG PET. After the initial uptake regions were selected, these high accumulation areas were automatically excluded from consideration thereafter. This method was repeated and new uptake regions were identified. This method was repeated up to five times. After that, the stacked-up uptake regions were compared with computed tomography (CT) images, and the high accumulation areas that were superimposed on the normal structures, such as intestine, vessels, and ureters, were excluded from the consideration. The remaining uptake regions were diagnosed as metastatic LNs, and the detectability of LN metastases was calculated. We then compared these statistical results with the results obtained on the basis of visual assessments by radiologists. RESULTS: Our proposed method showed the best results when the procedures were repeated three times in the light of detectability. After being repeated three times, this method detected 15/23 (65.2%) metastatic LNs in the first LN group, 16/16 (100%) in the second-third LN groups and 31/39 (79.4%) in the total LNs, whereas the radiologists diagnosed 8/23 (34.8%) of metastatic first LNs, 12/16 (75.0%) in the second-third LNs and 20/39 (51.3%) in the total LNs. A statistically significant difference was observed between the result of iteration number 3 and that by radiologists as for the second-third LNs and the total LNs. CONCLUSIONS: This study suggests that our proposed statistical method could improve the detectability of LN metastases from colorectal cancer. Our method will help radiologists to detect small metastatic lesions such as LN metastases.

[Examination of PET image evaluation experimentation method aiming at improved accuracy of data acquisition].

Multiple data evaluation is desirable for data obtained by positron emission tomography (PET), as the data follow the Poisson distribution. Such evaluation, however, tends to be very complicated, since the count- rates change with nuclide decay. To solve this problem, we propose a new data scan protocol in this communication. With this method, the true+scatter coincidence counts were computed during the initial one-minute scanning, which was fixed as the standard. A dynamic scan was then performed with the fixed counts from the high count-rate region. Regions with +/-2.5% of the image noise of the standard image was chosen to provide the data for evaluation. These were found to be the regions of 16.5-25.5 kcps (2D) and 81.1-138.5 kcps. Image quality was found to be affected by noise (2D) and random coincidence. Using this method, multiple data could be obtained by a single experiment, and very reliable image evaluation could be done.

Assessment of global and regional left ventricular function by electrocardiographic gated N-13 ammonia positron emission tomography in patients with coronary artery disease.

BACKGROUND: Electrocardiographic gated 13N-ammonia positron emission tomography (PET) enables simultaneous assessment of myocardial blood flow and left ventricular (LV) function. The aim of this study was to assess the accuracy of gated 13N-ammonia PET for evaluating global and regional LV function in patients with coronary artery disease (CAD) in comparison with conventional left ventriculography (LVG). METHODS AND RESULTS: Fifty-four patients with CAD underwent gated 13N-ammonia PET and LVG. The LV end-diastolic and end-systolic volumes (LVEDV, LVESV) and ejection fraction (LVEF) by gated 13N-ammonia PET were calculated using Cedars-Sinai automated quantitative gated single photon emission computed tomography (QGS) and compared with those obtained by LVG. The regional wall motion (RWM) was visually scored, and compared with that on LVG. There were good correlations between the 2 methods for LVEF, LVEDV and LVESV (R=0.828, R=0.821 and R=0.874 respectively). The RWM assessed by gated 13N-ammonia PET also agreed well with that by LVG (complete agreement was 70.4%, kappa=0.58). CONCLUSIONS: Gated 13N-ammonia PET combined with QGS works reasonably well for the assessment of both global and regional LV function in CAD patients, although additional calibration may be necessary.