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Benefits of Point-Spread Function and Time of Flight for PET/CT Image Quality in Relation to the Body Mass Index and Injected Dose

Akamatsu, Go, MS*; Mitsumoto, Katsuhiko, MS*; Ishikawa, Kaori, BS*; Taniguchi, Takafumi, BS*; Ohya, Nobuyoshi, PhD; Baba, Shingo, MD, PhD; Abe, Koichiro, MD, PhD; Sasaki, Masayuki, MD, PhD*

doi: 10.1097/RLU.0b013e31828da3bd
Original Articles

The PET image quality of overweight patients and patients who receive low injected doses deteriorates because of increases in statistical noise. The purpose of this study was to investigate the benefits of the point-spread function (PSF) and time-of-flight (TOF) for PET/CT image quality in such patients.

Methods The PET images were reconstructed using the baseline ordered-subsets expectation-maximization algorithm (OSEM), OSEM + PSF, OSEM + TOF, and OSEM + PSF + TOF. In the phantom study, we used a National Electrical Manufacturers Association body phantom with different radioactivity concentrations and analyzed image quality using the coefficient of variance in the background (CVphantom). In the clinical study, we retrospectively studied 39 patients who underwent clinical 18F-FDG PET/CT. The patients were classified into groups based on body mass index and injected dose. Image quality was evaluated using the CV in the liver (CVliver).

Results In the phantom study, PSF and TOF improved the CVphantom, especially in low-activity models. Among all of the reconstructions, the best CVphantom was obtained with OSEM + PSF + TOF. In the clinical study, the CVliver of the low-dose group with OSEM + PSF + TOF was comparable to that of the high-dose group with conventional OSEM.

Conclusions Point-spread function and TOF improved PET/CT image quality for overweight patients who received a lower injected dose. Therefore, the use of PSF and TOF is suggested to maintain the image quality of such patients without extending scanning times. It is greatly beneficial to obtain sufficient image quality for larger patients, especially in delivery institutions where the injection dose cannot be easily increased.

From the *Department of Health Sciences, Graduate School of Medical Sciences, Kyushu University; †Department of Medical Technology, Kyushu University Hospital; and ‡Department of Clinical Radiology, Graduate School of Medical Sciences, Kyushu University.

Received for publication October 3, 2012; revision accepted January 14, 2013.

Conflicts of interest and sources of funding: This study was supported in part by a grant-in aid for Scientific Research from the Japan Society for the Promotion of Science KAKENHI (22611012). The authors declare that they have no conflict of interest.

Reprints: Masayuki Sasaki, MD, PhD, Division of Medical Quantum Science, Department of Health Sciences, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan. E-mail:

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