The use of standardized uptake values (SUVs) is now common place in clinical 2-deoxy-2-[ 18 F] fluoro-D-glucose (FDG) position emission tomography-computed tomography oncology imaging and has a specific role in assessing patient response to cancer therapy. Ideally, the use of SUVs removes variability introduced by differences in patient size and the amount of injected FDG. However, in practice there are several sources of bias and variance that are introduced in the measurement of FDG uptake in tumors and also in the conversion of the image count data to SUVs. In this article the overall imaging process is reviewed and estimates of the magnitude of errors, where known, are given. Recommendations are provided for best practices in improving SUV accuracy.

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Positron emission tomography-computed tomography standardized uptake values in clinical practice and assessing response to therapy.

Human brown adipose tissue (BAT) can be activated to increase glucose uptake and energy expenditure, making it a potential target for treating obesity and metabolic disease. Data on the functional and anatomic characteristics of BAT are limited, however. In 20 healthy young men [12 lean, mean body mass index (BMI) 23.2 ± 1.9 kg/m2; 8 obese, BMI 34.8 ± 3.3 kg/m2] after 5 h of tolerable cold exposure, we measured BAT volume and activity by 18F-labeled fluorodeoxyglucose positron emission tomography/computerized tomography (PET/CT). Obese men had less activated BAT than lean men (mean, 130 vs. 334 mL) but more fat in BAT-containing depots (mean, 1,646 vs. 855 mL) with a wide range (0.1–71%) in the ratio of activated BAT to inactive fat between individuals. Six anatomic regions had activated BAT—cervical, supraclavicular, axillary, mediastinal, paraspinal, and abdominal—with 67 ± 20% of all activated BAT concentrated in a continuous fascial layer comprising the first three depots in the upper torso. These nonsubcutaneous fat depots amounted to 1.5% of total body mass (4.3% of total fat mass), and up to 90% of each depot could be activated BAT. The amount and activity of BAT was significantly influenced by region of interest selection methods, PET threshold criteria, and PET resolutions. The present study suggests that active BAT can be found in specific adipose depots in adult humans, but less than one-half of the fat in these depots is stimulated by acute cold exposure, demonstrating a previously underappreciated thermogenic potential.

https://www.pnas.org/content/pnas/114/32/8649.full.pdf

Mapping of human brown adipose tissue in lean and obese young men

Recommendations of the International Commission on Radiological Protection, ICRP Publication 2: Keport of Committee II on Permissible Dose for Internal Radiation (1959)., Pergamon Press (London, New York, Paris, Los Angeles), 1960, 233頁, 18.5×25.0cm, 1800円(丸善の価格)

TOF PET is characterized by a better trade-off between contrast and noise in the image. This property is enhanced in more challenging operating conditions, allowing for example shorter examinations or low counts, successful scanning of larger patients, low uptake, visualization of smaller lesions, and incomplete data sampling. In this paper, the correlation between the time resolution of a TOF PET scanner and the improvement in signal-to-noise in the image is introduced and discussed. A set of performance advantages is presented which include better image quality, shorter scan times, lower dose, higher spatial resolution, lower sensitivity to inconsistent data, and the opportunity for new architectures with missing angles. The recent scientific literature that reports the first experimental evidence of such advantages in oncology clinical data is reviewed. Finally, the directions for possible improvement of the time resolution of the present generation of TOF PET scanners are discussed.

Focus on time-of-flight PET: the benefits of improved time resolution.

These recommendations for measuring pulmonary nodules at computed tomography (CT) are a statement from the Fleischner Society and, as such, incorporate the opinions of a multidisciplinary international group of thoracic radiologists, pulmonologists, surgeons, pathologists, and other specialists. The recommendations address nodule size measurements at CT, which is a topic of importance, given that all available guidelines for nodule management are essentially based on nodule size or changes thereof. The recommendations are organized according to practical questions that commonly arise when nodules are measured in routine clinical practice and are, together with their answers, summarized in a table. The recommendations include technical requirements for accurate nodule measurement, directions on how to accurately measure the size of nodules at the workstation, and directions on how to report nodule size and changes in size. The recommendations are designed to provide practical advice based on the available evidence from the literature; however, areas of uncertainty are also discussed, and topics needing future research are highlighted. © RSNA, 2017 Online supplemental material is available for this article.

Recommendations for Measuring Pulmonary Nodules at CT: A Statement from the Fleischner Society.

OBJECTIVE. There is growing interest in using PET/CT for evaluating early response to therapy in cancer treatment. Although widely available and convenient to use, standardized uptake value (SUV) measurements can be influenced by a variety of biologic and technologic factors. Many of these factors can be addressed with close attention to detail and appropriate quality control. This article will review factors potentially affecting SUV measurements and provide recommendations on ways to minimize when using serial PET to assess early response to therapy.CONCLUSION. Scanner and reconstruction parameters can significantly affect SUV measurements. When using serial SUV measurements to assess early response to therapy, imaging should be performed on the same scanner using the same image acquisition and reconstruction protocols. In addition, attention to detail is required for accurate determination of the administered radiopharmaceutical dose.

https://www.ajronline.org/doi/pdfplus/10.2214/AJR.10.4923

A systematic review of the factors affecting accuracy of SUV measurements.

Purpose: This work involved the development of a phantom-based method to quantify the performance of tube current modulation and iterative reconstruction in modern computed tomography (CT) systems. The quantification included resolution, HU accuracy, noise, and noise texture accounting for the impact of contrast, prescribed dose, reconstruction algorithm, and body size. Methods: A 42-cm-long, 22.5-kg polyethylene phantom was designed to model four body sizes. Each size was represented by a uniform section, for the measurement of the noise-power spectrum (NPS), and a feature section containing various rods, for the measurement of HU and the task-based modulation transfer function (TTF). The phantom was scanned on a clinical CT system (GE, 750HD) using a range of tube current modulation settings (NI levels) and reconstruction methods (FBP and ASIR30). An image quality analysis program was developed to process the phantom data to calculate the targeted image quality metrics as a function of contrast, prescribed dose, and body size. Results: The phantom fabrication closely followed the design specifications. In terms of tube current modulation, the tube current and resulting image noise varied as a function of phantom size as expected based on the manufacturer specification: From the 16- to 37-cm section, the HU contrast for each rod was inversely related to phantom size, and noise was relatively constant (<5% change). With iterative reconstruction, the TTF exhibited a contrast dependency with better performance for higher contrast objects. At low noise levels, TTFs of iterative reconstruction were better than those of FBP, but at higher noise, that superiority was not maintained at all contrast levels. Relative to FBP, the NPS of iterative reconstruction exhibited an ∼30% decrease in magnitude and a 0.1 mm−1 shift in the peak frequency. Conclusions: Phantom and image quality analysis software were created for assessing CT image quality over a range of contrasts, doses, and body sizes. The testing platform enabled robust NPS, TTF, HU, and pixel noise measurements as a function of body size capable of characterizing the performance of reconstruction algorithms and tube current modulation techniques.

A methodology for image quality evaluation of advanced CT systems.

Purpose: For nonlinear iterative image reconstructions (IR), the computed tomography (CT) noise and resolution properties can depend on the specific imaging conditions, such as lesion contrast and image noise level. Therefore, it is imperative to develop a reliable method to measure the noise and resolution properties under clinically relevant conditions. This study aimed to develop a robust methodology to measure the three-dimensional CT noise and resolution properties under such conditions and to provide guidelines to achieve desirable levels of accuracy and precision. Methods: The methodology was developed based on a previously reported CT image quality phantom. In this methodology, CT noise properties are measured in the uniform region of the phantom in terms of a task-based 3D noise-power spectrum (NPS{sub task}). The in-plane resolution properties are measured in terms of the task transfer function (TTF) by applying a radial edge technique to the rod inserts in the phantom. The z-direction resolution properties are measured from a supplemental phantom, also in terms of the TTF. To account for the possible nonlinearity of IR, the NPS{sub task} is measured with respect to the noise magnitude, and the TTF with respect to noise magnitude and edge contrast. To determine the accuracy and precisionmore » of the methodology, images of known noise and resolution properties were simulated. The NPS{sub task} and TTF were measured on the simulated images and compared to the truth, with criteria established to achieve NPS{sub task} and TTF measurements with <10% error. To demonstrate the utility of this methodology, measurements were performed on a commercial CT system using five dose levels, two slice thicknesses, and three reconstruction algorithms (filtered backprojection, FBP; iterative reconstruction in imaging space, IRIS; and sinogram affirmed iterative reconstruction with strengths of 5, SAFIRE5). Results: To achieve NPS{sub task} measurements with <10% error, the number of regions of interest needed to be greater than 65. To achieve TTF measurements with <10% error, the contrast-to-noise ratio of the edge needed to be ≥15, achievable by averaging multiple slices across the same edge. The NPS{sub task} measured on a commercial CT system showed IR's reduced noise (IRIS, 30% and SAFIRE5, 55%) and “waxier” texture (peak frequencies: FBP, 0.25 mm{sup −1}; IRIS, 0.23 mm{sup −1}; and SAFIRE5, 0.16 mm{sup −1}). The TTF measured within the axial plane showed improved in-plane resolution with SAFIRE5 at the TTF 50% frequency, f{sub 50} (FBP, 0.36–0.41 mm{sup −1}; SAFIRE5, 0.37–0.46 mm{sup −1}). The TTF measured along the axial direction showed improved z-direction resolution with thinner slice thickness (f{sub 50}: 0.6 mm, 0.35–0.79 mm{sup −1}; 1.5 mm, 0.22–0.3 mm{sup −1}) and with SAFIRE5 (f{sub 50}: FBP, 0.35–0.52 mm{sup −1}; SAFIRE5, 0.42–0.79 mm{sup −1}). Both in-plane and z-direction resolution of SAFIRE5 showed strong dependency on contrast, reflecting SAFIRE5's nonlinearity. Conclusions: A methodology was developed to measure three-dimensional CT noise and resolution properties for iterative reconstruction, especially at challenging measurement conditions with low contrast and high image noise. The methodology also demonstrated its utility for evaluating commercial CT systems.« less

Assessment of volumetric noise and resolution performance for linear and nonlinear CT reconstruction methods.

Our study results show that dual-energy multi–detector row CT with reconstruction of optimal-energy virtual monochromatic images can overcome renal cyst pseudoenhancement.

Impact of Dual-Energy Multi–Detector Row CT with Virtual Monochromatic Imaging on Renal Cyst Pseudoenhancement: In Vitro and in Vivo Study

Purpose:
The purpose of this work was to assess the inherent image quality characteristics of a new multidetector computed tomography system in terms of noise, resolution, and detectability index as a function of image acquisition and reconstruction for a range of clinically relevant settings.

Methods:
A multisized image quality phantom (37, 30, 23, 18.5, and 12 cm physical diameter) was imaged on a SOMATOM Force scanner (Siemens Medical Solutions) under variable dose, kVp, and tube current modulation settings. Images were reconstructed with filtered back projection (FBP) and with advanced modeled iterative reconstruction (ADMIRE) with iterative strengths of 3, 4, and 5. Image quality was assessed in terms of the noise power spectrum (NPS), task transfer function (TTF), and detectability index for a range of detection tasks (contrasts of approximately 45, 90, 300, −900, and 1000 HU, and 2–20 mm diameter) based on a non-prewhitening matched filter model observer with eye filter.

Results:
Image noise magnitude decreased with decreasing phantom size, increasing dose, and increasing ADMIRE strength, offering up to 64% noise reduction relative to FBP. Noise texture in terms of the NPS was similar between FBP and ADMIRE (<5% shift in peak frequency). The resolution, based on the TTF, improved with increased ADMIRE strength by an average of 15% in the TTF 50% frequency for ADMIRE-5. The detectability index increased with increasing dose and ADMIRE strength by an average of 55%, 90%, and 163% for ADMIRE 3, 4, and 5, respectively. Assessing the impact of mA modulation for a fixed average dose over the length of the phantom, detectability was up to 49% lower in smaller phantom sections and up to 26% higher in larger phantom sections for the modulated scan compared to a fixed tube current scan. Overall, the detectability exhibited less variability with phantom size for modulated scans compared to fixed tube current scans.

Conclusions:
Image quality increased with increasing dose and decreasing phantom size. The CT system exhibited nonlinear noise and resolution properties, especially at very low-doses, large phantom sizes, and for low-contrast objects. Objective image quality metrics generally increased with increasing dose and ADMIRE strength, and with decreasing phantom size. The ADMIRE algorithm could offer comparable image quality at reduced doses or improved image quality at the same dose. The use of tube current modulation resulted in more consistent image quality with changing phantom size.

Joshua M. Wilson

Papers

A systematic review of the factors affecting accuracy of SUV measurements.

A methodology for image quality evaluation of advanced CT systems.

Assessment of volumetric noise and resolution performance for linear and nonlinear CT reconstruction methods.

Impact of Dual-Energy Multi–Detector Row CT with Virtual Monochromatic Imaging on Renal Cyst Pseudoenhancement: In Vitro and in Vivo Study

Characteristic image quality of a third generation dual-source MDCT scanner: Noise, resolution, and detectability.