Effect of Tumor-Pixel Positioning on the Variability of SUV Measurements in PET Images.

Objectives: The aim of this study was to investigate the effect on standardized uptake value (SUV) measurement variability of the positional relationship between objects of different sizes and the pixel of a positron emission tomography (PET) image. Methods: We used a NEMA IEC body phantom comprising six spheres with diameters of 10, 13, 17, 22, 28, and 37 mm. The phantom was filled with 18F solution and contained target-to-background ratios (TBRs) of 2, 4, and 8. The PET data were acquired for 30 min using a SIGNA PET/MR scanner. The PET images were reconstructed with the ordered subsets expectation maximization (OSEM) algorithm with and without point-spread function (PSF) correction (OSEM + PSF + Filter and OSEM + Filter, respectively). A Gaussian filter of 4 mm full width at half maximum was applied in all reconstructions, except for one model (OSEM + PSF + no Filter). The matrix sizes were 128×128, 192×192, 256×256 and 384×384. Reconstruction was performed by shifting the reconstruction center position by 1 mm in the range 0 to 3 mm in the upward or rightward direction for each parameter. For all reconstructed images, the SUVmax of each hot sphere was measured. To investigate the resulting variation in the SUVmax, the coefficient of variation (CV) of each SUVmax was calculated. Results: The CV of the SUVmax increased as the matrix size and the diameter of the hot sphere decreased in all reconstruction settings. With PSF correction, the CV of SUVmax increased as the TBR increased except when the TBR was 2. The CV of the SUVmax measured in the OSEM + PSF + no Filter images were larger than those measured in the OSEM + PSF + Filter images. The amount of this increase was higher for smaller spheres and larger matrix sizes and was independent of TBR. Conclusions: Shifting the reconstruction center position of the PET image causes variability in SUVmax measurements. To reduce the variability of SUV measurements, it is necessary to use sufficient matrix sizes to satisfy sampling criterion and appropriate filters.

Multicentre analysis of PET SUV using vendor-neutral software: the Japanese Harmonization Technology (J-Hart) study.

BACKGROUND: Recent developments in hardware and software for PET technologies have resulted in wide variations in basic performance. Multicentre studies require a standard imaging protocol and SUV harmonization to reduce inter- and intra-scanner variability in the SUV. The Japanese standardised uptake value (SUV) Harmonization Technology (J-Hart) study aimed to determine the applicability of vendor-neutral software on the SUV derived from positron emission tomography (PET) images. The effects of SUV harmonization were evaluated based on the reproducibility of several scanners and the repeatability of an individual scanner. Images were acquired from 12 PET scanners at nine institutions. PET images were acquired over a period of 30 min from a National Electrical Manufacturers Association (NEMA) International Electrotechnical Commission (IEC) body phantom containing six spheres of different diameters and an 18F solution with a background activity of 2.65 kBq/mL and a sphere-to-background ratio of 4. The images were reconstructed to determine parameters for harmonization and to evaluate reproducibility. PET images with 2-min acquisition × 15 contiguous frames were reconstructed to evaluate repeatability. Various Gaussian filters (GFs) with full-width at half maximum (FWHM) values ranging from 1 to 15 mm in 1-mm increments were also applied using vendor-neutral software. The SUVmax of spheres was compared with the reference range proposed by the Japanese Society of Nuclear Medicine (JSNM) and the digital reference object (DRO) of the NEMA phantom. The coefficient of variation (CV) of the SUVmax determined using 12 PET scanners (CVrepro) was measured to evaluate reproducibility. The CV of the SUVmax determined from 15 frames (CVrepeat) per PET scanner was measured to determine repeatability. RESULTS: Three PET scanners did not require an additional GF for harmonization, whereas the other nine required additional FWHM values of GF ranging from 5 to 9 mm. The pre- and post-harmonization CVrepro of six spheres were (means ± SD) 9.45% ± 4.69% (range, 3.83-15.3%) and 6.05% ± 3.61% (range, 2.30-10.7%), respectively. Harmonization significantly improved reproducibility of PET SUVmax (P = 0.0055). The pre- and post-harmonization CVrepeat of nine scanners were (means ± SD) 6.59% ± 1.29% (range, 5.00-8.98%) and 4.88% ± 1.64% (range, 2.65-6.72%), respectively. Harmonization also significantly improved the repeatability of PET SUVmax (P < 0.0001). CONCLUSIONS: Harmonizing SUV using vendor-neutral software produced SUVmax for 12 scanners that fell within the JSNM reference range of a NEMA body phantom and improved SUVmax reproducibility and repeatability.

Performance Evaluation of a New Dedicated Breast PET Scanner Using NEMA NU4-2008 Standards.

UNLABELLED: The aim of this work was to evaluate the performance characteristics of a newly developed dedicated breast PET scanner, according to National Electrical Manufacturers Association (NEMA) NU 4-2008 standards. METHODS: The dedicated breast PET scanner consists of 4 layers of a 32 × 32 lutetium oxyorthosilicate-based crystal array, a light guide, and a 64-channel position-sensitive photomultiplier tube. The size of a crystal element is 1.44 × 1.44 × 4.5 mm. The detector ring has a large solid angle with a 185-mm aperture and an axial coverage of 155.5 mm. The energy windows at depth of interaction for the first and second layers are 400-800 keV, and those at the third and fourth layers are 100-800 keV. A fixed timing window of 4.5 ns was used for all acquisitions. Spatial resolution, sensitivity, counting rate capabilities, and image quality were evaluated in accordance with NEMA NU 4-2008 standards. Human imaging was performed in addition to the evaluation. RESULTS: Radial, tangential, and axial spatial resolution measured as minimal full width at half maximum approached 1.6, 1.7, and 2.0 mm, respectively, for filtered backprojection reconstruction and 0.8, 0.8, and 0.8 mm, respectively, for dynamic row-action maximum-likelihood algorithm reconstruction. The peak absolute sensitivity of the system was 11.2%. Scatter fraction at the same acquisition settings was 30.1% for the rat-sized phantom. Peak noise-equivalent counting rate and peak true rate for the ratlike phantom was 374 kcps at 25 MBq and 603 kcps at 31 MBq, respectively. In the image-quality phantom study, recovery coefficients and uniformity were 0.04-0.82 and 1.9%, respectively, for standard reconstruction mode and 0.09-0.97 and 4.5%, respectively, for enhanced-resolution mode. Human imaging provided high-contrast images with restricted background noise for standard reconstruction mode and high-resolution images for enhanced-resolution mode. CONCLUSION: The dedicated breast PET scanner has excellent spatial resolution and high sensitivity. The performance of the dedicated breast PET scanner is considered to be reasonable enough to support its use in breast cancer imaging.

[The examination of attenuation correction using one computed tomography scan in myocardial perfusion stress-rest single photon emission computed tomography].

Attenuation correction (AC) of myocardial perfusion stress-rest single photon emission computed tomography (SPECT) with hybrid SPECT/computed tomography (CT) is effective. But because CT scan is done two times, the radiation exposure of patients increases. Therefore, we suggested a new method of AC that can correct attenuation of SPECT images acquired during a rest examination by using the CT scan during a stress examination. AC was done using one CT scan and we evaluated the clinical appropriateness of using this method. Matters of this study were (1) positional reproducibility of data analysis machine (Xeleris) (2) phantom study: accuracy of registration by manual and repetition reproducibility (3) clinical study using (99m)Tc-tetrofosmin. Comparison methods were analyzed by calculating the difference perfusion (Dp) with 17-segments model of American Heart Association and visual evaluation of three axis images in the myocardium. In the phantom study, because most of the score of 17-segments accord (Dp≤1), it was considered that the shift on SPECT/CT's bed was reproduced by the shift on Xeleris. And it is shown that AC with CT scan on deference point was accuracy. In the clinical study, there were a few differences in Dp (Dp≤4) and approximately equal evaluation on visual evaluation was provided, which compared with conventional methods. Because AC of myocardial perfusion stress-rest SPECT by one CT scan showed that it was approximately equal in evaluation compared with conventional methods, we expect to be able to use this method in clinical cases.

Delayed initial radioactive iodine therapy resulted in poor survival in patients with metastatic differentiated thyroid carcinoma: a retrospective statistical analysis of 198 cases.

UNLABELLED: To elucidate the prognostic role of (131)I radioactive iodine therapy (RIT), we conducted a retrospective cohort study analyzing the clinical factors that affect survival of postoperative patients with differentiated thyroid carcinoma (DTC). METHODS: We included 198 DTC patients with extrathyroidal extension who received total or near-total thyroidectomy and then RIT in our hospital from January 1997 to June 2009: patients with lymph node metastases only (n = 47), lung metastases without bone metastases (n = 105), or bone metastases and other distant metastases (lung, liver, brain, and skin) (n = 46). Hemithyroidectomy or subtotal thyroidectomy had been performed before total or near-total thyroidectomy in 59 patients. Disease-specific survival after initial RIT was statistically evaluated using relevant clinical parameters, including age at initial RIT, pathology, sex, therapeutic history before initial RIT, pre- and posttherapeutic serum thyroglobulin ("prethyroglobulin" and "postthyroglobulin," respectively) at initial RIT, thyroglobulin under thyroid-stimulating hormone stimulation at initial RIT ("peak thyroglobulin"), grade of uptake at scintigraphy, extent of metastasis, and number of total RITs. RESULTS: During follow-up after initial RIT (average, 5.37 y), 24 patients died from DTC (11 male patients and 13 female). The most common reasons for death were respiratory failure due to lung metastases (n = 11) and uncontrollable brain metastases (n = 6). Univariate analysis showed that disease-specific survival was related to the following factors: extent of metastasis, age at initial RIT (<45 y), prethyroglobulin (<125 ng/mL), peak thyroglobulin (<1,000 ng/mL), and interval from total thyroidectomy to initial RIT (<180 d). A past history of hemithyroidectomy or subtotal thyroidectomy was not related to disease-specific survival. Multivariate analysis showed 3 factors to be independent prognostic factors--grade of (131)I uptake at whole-body scintigraphy, extent of metastasis, and interval to RIT (P ≤ 0.001, 0.010, and 0.005, respectively)--and also showed that risk of death in patients with an interval over 180 d was 4.22 times higher than in those with an interval within 180 d. Kaplan-Meier analysis revealed that a shorter interval (180, 365, or 1,000 d) had prognostic value even in the subgroups 45 y or older, with lung metastases, and with bone metastases or more. CONCLUSION: The present study suggests that delaying initial RIT until more than 180 d after total thyroidectomy may result in poor survival for DTC patients.

Significance of chronic marked hyperglycemia on FDG-PET: is it really problematic for clinical oncologic imaging?

OBJECTIVES: The purpose of this study was to evaluate the adverse effects of chronic marked hyperglycemia on clinical diagnostic performance of positron emission tomography (PET) using (18)F-fuorodeoxyglucose (FDG). METHODS: Fifty-seven scans of 54 patients, who received FDG-PET for the diagnosis of various cancer(s), and who showed high plasma glucose level of more than 200 mg/dl at the time of administration of FDG in spite of at least 4-h fasting, were retrospectively analyzed. In the clinical follow-up, this high plasma glucose was confirmed as chronic hyperglycemia derived from uncontrolled diabetes (n = 32) and untreated diabetes (n = 25). Based on the final diagnosis of malignancy obtained by histopathology or clinical follow-up for at least 6 months, the diagnostic performance of visual PET analysis was evaluated. RESULTS: Excluding nine scans of nine patients without sufficient follow-up, final diagnosis was obtained in 48 scans of 45 patients. In 36 scans of 36 patients, at least one malignant lesion was finally confirmed, and true-positive and false-negative results were obtained in 30 and six cases, respectively. Six cases showed false-negative results due to low FDG-avid pathological characteristics (hepatocellular carcinoma, etc.), chemotherapeutic effect or small tumor size. Overall, the patient-based sensitivity, specificity, positive predictive value, negative predictive value and diagnostic accuracy were 83, 83, 94, 63 and 83%, respectively. In lesion-based diagnosis, 56 of 75 lesions (74%) were depicted by PET, while 19 lesions were negative on PET, also due to low FDG-avid characteristics or small size (less than 15 mm). CONCLUSIONS: At the time of chronic hyperglycemia (not acute hyperglycemia), the adverse effect caused by high plasma glucose level was minimum. The FDG uptake of the tumor maintained a sufficiently high level for visual clinical diagnosis in most cases, except in the cases of low FDG-avid tumors or small lesions (15 mm in size).

Diagnostic accuracy of bone metastases detection in cancer patients: comparison between bone scintigraphy and whole-body FDG-PET.

UNLABELLED: 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) has become widely available and an important oncological technique. To evaluate the influence of PET on detection of bone metastasis, we compared the diagnostic accuracy of PET and conventional bone scintigraphy (BS) in a variety of cancer patients. METHODS: Consecutive ninety-five patients with various cancers, who received both PET and BS within one month, were retrospectively analyzed. A whole-body PET (from face to upper thigh) and a standard whole body BS were performed and these images were interpreted by two experienced nuclear medicine physicians with and without patient information using monitor diagnosis. Each image interpretation was performed according to 8 separate areas (skull, vertebra, upper limbs, sternum and clavicles, scapula, ribs, pelvis, and lower limbs) using a 5-point-scale (0: definitely negative, 1: probably negative, 2: equivocal, 3: probably positive, 4: definitely positive for bone metastasis). RESULTS: Twenty-one of 95 patients (22.1%) with 43 of 760 areas (5.7%) of bone metastases were finally confirmed. In untreated patients, 12 of 14 bone metastasis positive patients were detected by PET, while 9 of 14 were detected by BS. Three cases showed true positive in PET and false negative in BS due to osteolytic type bone metastases. In untreated cases, PET with and without clinical information showed better sensitivity than BS in patient-based diagnosis. For the purpose of treatment effect evaluation, PET showed better results because of its ability in the evaluation of rapid response of tumor cells to chemotherapy. Out of 10 cases of multiple-area metastases, 9 cases included vertebrae. There was only one solitary lesion located outside of FOV of PET scan in the femur, but with clinical information that was no problem for PET diagnosis. CONCLUSION: Diagnostic accuracy of bone metastasis was comparable in PET and BS in the present study. In a usual clinical condition, limited FOV (from face to upper thigh) of PET scan may not be a major drawback in the detection of bone metastases because of the relatively low risk of solitary bone metastasis in skull bone and lower limbs.