Optimization of scanning time of 18F-FDG whole body PET/CT imaging in obese patients using quadratic dose protocol.

INTRODUCTION: 18F-FDG imaging of overweight and obese patients is often challenging due to higher scattering and attenuation. Degradation of positron emission tomography (PET) image quality as the body weight increases is best overcome by using the quadratic dose protocol. Previously the implementation of this protocol on a Bismuth Germanium Oxide (BGO) scintillation crystal-based PET/CT system at Institut Kanser Negara (IKN), Malaysia practices using the linear dose protocol (Tmin=2.5 minutes). Hence, this study aims to optimize the Tmin of the quadratic dose protocol for 18F-FDG PET/CT. MATERIALS AND METHODS: This study was conducted based on the guideline published by the European Association of Nuclear Medicine (EANM) version 2.0 FDG-PET/CT and conducted in two phases. Firstly, 100 whole-body scan 18FFDG PET/CT images were selected for the average coefficient of variation (COV) analysis in the liver region. Second, a NEMA 2012/IEC2008 phantom was used to obtain the relationship between the COVphantom and the scanning time. Finally, the images acquired using the two Tmin were quantitatively compared using contrast recovery coefficient (QH), signal to noise ratio (SNR), and visibility (VH). Independent t-test between each image quality parameter performed with p-value <0.05 considered significant. RESULTS: The average COV of the liver was 17.7%. Currently, this value was clinically accepted to produce appropriate image quality at IKN. Interpolation at COV=17.7% gave a Tmin value of 2.9 minutes. Comparisons show that the two Tmin yielded equivalent PET/CT image quality (p-value of QH=0.774, SNR=0.780 and VH=0.915). CONCLUSION: The optimal Tmin defined in this study was 2.9 minutes, 27.6% shorter than the Tmin previously defined based on COV=15%. Despite the higher average COV, the shorter Tmin beneficial in the lower total 18F-FDG activity administered, reduce the internal dose to the patient while producing equivalent image quality.

The need of a system phantom for quantitative hybrid nuclear imaging of PET/CT: A systematic review.

INTRODUCTION: There has already been a rising demand in utilising phantom for hybrid Positron Emission Tomography/ Computed Tomography (PET/CT) scanner of nuclear imaging. This review further clarifies this topic and investigates how the previous research phantoms operated with the need for quantitative hybrid nuclear imaging of PET/CT while providing a relatively high image quality when it was performed. In this article, the necessity of previous and current phantom studies in hybrid nuclear imaging of PET/CT scanners is reviewed. METHODS: PubMed and Google Scholar were systematically searched for the relevant studies by following the PRISMA 2009 checklist. A past decade literature search was conducted from 2010 until November 2020 to secure the relevance of the phantom study. Databases were recruited using keywords such as phantom, quantification, standardisation, harmonisation, image quality, standardised uptake value and multicentre study. However, all keywords were related to PET/CT. All abstracts and eligible full-text articles were screened independently, and finally, the quality assessments of this review were performed. RESULTS: From the 200 retrieved articles, 80 were rejected after the screening of the abstracts and 35 after reading the full-text. The 20 accepted articles addressed the distribution of phantom types used in selected articles studies which were NEMA (67%), ACR (8%) and others (25%). The articles showed the various experimental studies, either phantom studies (35%) or phantom plus clinical studies (65%). For clinical studies (n = 829), the distribution of prospective studies was (n = 674) and retrospective studies was (n =155). The distribution of phantom pathway application showed the studies focused on 40% of reconstruction protocol studies, 30% of the multicentre and standardisation of accreditation program studies, and 30% of the quantification of uptake values studies. CONCLUSIONS: According to this review, the phantom study have a pivotal role in hybrid nuclear imaging of PET/CT either in technical aspects of the scanners (such as data acquisition and reconstruction protocol) or clinical characteristics of patients. In addition to this, the necessity to identify the suitable system phantoms to use within PET/CT scans by considering the continuous development of new phantom studies are needed. Researchers are encouraged to adopt efforts on phantom quantitative validation, including verification with clinical data of patients.

Dose perturbation effects by metal hip prosthesis in gynaecological 192Ir HDR brachytherapy.

The present study was conducted to elucidate the effects of hip prostheses in 192Ir HDR brachytherapy and determine dose uncertainties introduced by the treatment planning. A gynaecological phantom irradiated using Nucletron 192Ir microSelectron HDR source was modeled using MCNP5 code. Three hip materials considered in this study were water, bone, and metal prosthesis. According to the obtained results, a dose perturbation was observed within the medium with a higher atomic number, which reduced the dose to the nearby region.