Whole-body PET/CT scanning: estimation of radiation dose and cancer risk.

PURPOSE: To estimate the radiation dose from whole-body fluorine 18 ((18)F)-fluorodeoxyglucose (FDG) positron emission tomographic (PET)/computed tomographic (CT) studies and to evaluate the induced cancer risk to U.S. and Hong Kong populations. MATERIALS AND METHODS: Fluorine 18-FDG PET/CT studies obtained by using a 64-detector CT unit and one of three CT protocols were evaluated. CT protocol A consisted of 120 kV; rotation time, 0.5 second; pitch, 0.984; 100-300 mA; and noise level, 20. CT protocol B was the same as A, except for a fixed tube current of 250 mA. CT protocol C consisted of 140 kV; rotation time, 0.5 second; pitch, 0.984; 150-350 mA; and noise level, 3.5. CT doses were measured in a humanoid phantom equipped with thermoluminescent dosimeters. Doses from (18)F-FDG PET scanning were estimated by multiplying the (18)F-FDG radioactivity (370 MBq) with dose coefficients. Effective doses were calculated according to International Commission on Radiological Protection publication 103. Lifetime attributable risk (LAR) of cancer incidence was estimated according to the National Academies' Biological Effects of Ionizing Radiation VII Report. RESULTS: Effective doses with protocols A, B, and C, respectively, were 13.45, 24.79, and 31.91 mSv for female patients and 13.65, 24.80, and 32.18 mSv for male patients. The LAR of cancer incidence associated with the dose was higher in the Hong Kong population than in the U.S. population. For 20-year-old U.S. women, LARs of cancer incidence were between 0.231% and 0.514%, and for 20-year-old U.S. men, LARs of cancer incidence were between 0.163% and 0.323%; LARs were 5.5%-20.9% higher for the Hong Kong population. The induced cancer risks decreased when age at exposure increased. CONCLUSION: Whole-body PET/CT scanning is accompanied by substantial radiation dose and cancer risk. Thus, examinations should be clinically justified, and measures should be taken to reduce the dose.

Pediatric 64-MDCT coronary angiography with ECG-modulated tube current: radiation dose and cancer risk.

OBJECTIVE: The purpose of our study was to measure the radiation dose from ECG-gated CT coronary angiography in children and to estimate the cancer risk associated with the radiation dose. MATERIALS AND METHODS: Organ doses were measured with a 5-year-old pediatric phantom and thermoluminescent dosimeters on a 64-MDCT scanner. Four retrospectively ECG-gated CT coronary angiography protocols with four simulated heart rates and the corresponding pitches were studied. The lifetime attributable risk of cancer incidence was estimated for children in the United States and Hong Kong according to the National Academies Biologic Effects of Ionizing Radiation VII report. RESULTS: The effective doses were 16.45, 12.17, 11.97, and 11.81 mSv for the four protocols, respectively. The corresponding lifetime attributable risks estimated for 5-year-old U.S. boys and girls were 0.14%-0.20% and 0.43%-0.60%, respectively, and for 5-year-old Hong Kong boys and girls were 0.22%-0.33% and 0.61%-0.85%. In relation to the total cancer incidence (baseline cancer incidence plus lifetime attributable risk), lifetime attributable risk from radiation exposure contributed up to 0.99% and 3.51% for Hong Kong boys and girls and up to 0.46% and 1.57% for U.S. boys and girls. CONCLUSION: Our results suggest that radiation dose and cancer risk of CT coronary angiography to pediatric patients are not negligible, more so in Hong Kong children than in U.S. children. Therefore, these examinations should be well justified clinically.

Comparison of image quality and radiation exposure between conventional imaging and gemstone spectral imaging in abdominal CT examination.

OBJECTIVE: To compare patients' image quality and radiation exposure between gemstone spectral imaging (GSI) with rapid kV switching technique and conventional polychromatic imaging (CPI) performed in abdominal CT examinations. METHODS: Adult patients who were referred to abdominal CT from October 2015 to March 2016 were enrolled. Unenhanced CT with CPI mode and tri-phase (arterial/portal/delayed phase) contrast-enhanced scan with GSI mode were performed with different protocols respectively. Regions of interest (ROIs) were drawn on muscle and fat. Parametric results of the image noise, signal-to-noise ratio (SNR) and clinical image quality in these regions between the monochromatic images reconstructed at 65 keV and conventional polychromatic images were compared. Radiation dose was also compared between CPI and GSI. RESULTS: 43 patients were recruited. Compared to conventional imaging, the noise level was generally not significantly different between GSI images in arterial phase and portal phase, and significantly higher (around 10%) in delayed phase. The SNR of GSI in portal phase was significantly higher than that of conventional imaging, and was similar between arterial phase/delayed phase and conventional imaging. The clinical image quality between conventional imaging and GSI was generally not significantly different. The dose length product was reduced by 0.3-20.1% in GSI compared to conventional imaging. CONCLUSION: GSI reduces the radiation exposure slightly, however maintains or even improves image quality. These results may warrant the application of GSI in patients referred for abdominal CT. Advances in knowledge: Compared to CPI, GSI reduces the radiation exposure slightly, however maintains or even improves image quality in abdominal CT. These findings may warrant the application of GSI in patients referred for abdominal CT.

Opportunistic screening for osteoporosis in abdominal computed tomography for Chinese population.

This study assessed the possibility of diagnosing and excluding osteoporosis with routine abdominal CT scans in a Chinese population who underwent both DXA and CT for unrelated reasons. Statistical correlation was made between the HU measured of the spine on CT and various parameters on DXA. Diagnostic cutoff points in terms of HU were established for the diagnosis (≤ 136 HU) and exclusion (≥ 175 HU) of osteoporosis on sagittal reformatted images. There was excellent positive and negative predictive value for the DXA-defined diagnostic subgroups and were also comparable with previous studies in Caucasian populations. The authors exhort radiologists to report these incidental findings to facilitate early detection and treatment of osteoporosis in unsuspecting patients to prevent fractures and related complications. PURPOSE: The suspicion for osteoporosis can be raised in diagnostic computed tomography of the abdomen performed for other indications. We derived cutoff thresholds for the attenuation value of the lumbar spinal vertebrae (L1-5) in Hounsfield units (HU) in a Chinese patient population to facilitate implementation of opportunistic screening in radiologists. METHODS: We included 109 Chinese patients who concomitantly underwent abdominal CT and dual X-ray absorptiometry (DXA) within 6 months between July 2014 and July 2017 at a university hospital in Hong Kong. Images were retrospectively reviewed on sagittal reformats, and region-of-interest (ROI) markers were placed on the anterior portion of each of the L1-L5 vertebra to measure the HU. The mean values of CT HU were then compared with the bone mineral density (BMD) and T-score obtained by DXA. Receiver operator characteristic (ROC) curves were generated to determine diagnostic cutoff thresholds and their sensitivity and specificity values. RESULTS: The mean CT HU differed significantly (p < 0.01) for the three DXA-defined BMD categories of osteoporosis (97 HU), of osteopenia (135 HU), and of normal individuals (230 HU). There was good correlation between the mean CT HU and BMD and T-score (Pearson coefficient of 0.62 and 0.61, respectively, p < 0.001). The optimal cutoff point for exclusion of osteoporosis or osteopenia was HU ≥ 175 with negative predictive value as 98.9% and with area under curve (AUC) of ROC curve as 0.97. The optimal cutoff point for diagnosis of osteoporosis was HU ≤ 136 with positive predictive value as 81.2% and with AUC of ROC curve as 0.86. CONCLUSION: This is the first study on osteoporosis diagnosis with routine CT abdominal scans in Chinese population. The cutoff values were comparable with previous studies in Caucasian populations suggesting generalizability. Radiologists should consider routinely reporting these opportunistic findings to facilitate early detection and treatment of osteoporosis to prevent fractures and related complications.

Percutaneous cholecystostomy for high-risk patients with acute cholangitis.

Percutaneous cholecystostomy (PC) is a well-established treatment for acute cholecystitis. We investigate the performance and role of PC in managing acute cholangitis.Retrospective review on all patients who underwent PC for acute cholangitis between January 2012 and June 2017 at a major regional hospital in Hong Kong.Thirty-two patients were included. The median age was 84 years and median American Society of Anaesthesiologists (ASA) physical status was Class III (severe systemic disease). All fulfilled Tokyo Guidelines 2013 (TG13) diagnostic criteria for moderate or severe cholangitis. Eighty-four percent of the patients were shown to have lower common bile duct stones on imaging. The majority had previously failed intervention by endoscopic retrograde cholangiopancreatography (38%), percutaneous transhepatic biliary drainage (38%), or both (13%)The technical success rate for PC was 100% with no procedure-related mortality. The overall 30-day mortality was 9%. Rest of the patients (91%) had significant improvement in clinical symptoms and could be discharged with median length of stay of 14 days. Significant postprocedural biochemical improvement was observed in terms of white cell count (P < .001), serum bilirubin (P < .001), alkaline phosphatase (P = .001), and alanine transaminase levels (P < .001). Time from admission to PC was associated with excess mortality (P = .002).PC is an effective treatment for acute cholangitis in high-risk elderly patients. Early intervention is associated with lower mortality. PC is particularly valuable as a temporising measure before definitive treatment in critical patients or as salvage therapy where other methods endoscopic retrograde cholangiopancreatography/percutaneous transhepatic biliary drainage (ERCP/PTBD) have failed.

Radiation dose and cancer risk from pediatric CT examinations on 64-slice CT: a phantom study.

OBJECTIVE: To measure the radiation dose from CT scans in an anthropomorphic phantom using a 64-slice MDCT, and to estimate the associated cancer risk. MATERIALS AND METHODS: Organ doses were measured with a 5-year-old phantom and thermoluminescent dosimeters. Four protocols; head CT, thorax CT, abdomen CT and pelvis CT were studied. Cancer risks, in the form of lifetime attributable risk (LAR) of cancer incidence, were estimated by linear extrapolation using the organ radiation doses and the LAR data. RESULTS: The effective doses for head, thorax, abdomen and pelvis CT, were 0.7mSv, 3.5mSv, 3.0mSv, 1.3mSv respectively. The organs with the highest dose were; for head CT, salivary gland (22.33mGy); for thorax CT, breast (7.89mGy); for abdomen CT, colon (6.62mGy); for pelvis CT, bladder (4.28mGy). The corresponding LARs for boys and girls were 0.015-0.053% and 0.034-0.155% respectively. The organs with highest LARs were; for head CT, thyroid gland (0.003% for boys, 0.015% for girls); for thorax CT, lung for boys (0.014%) and breast for girls (0.069%); for abdomen CT, colon for boys (0.017%) and lung for girls (0.016%); for pelvis CT, bladder for both boys and girls (0.008%). CONCLUSION: The effective doses from these common pediatric CT examinations ranged from 0.7mSv to 3.5mSv and the associated lifetime cancer risks were found to be up to 0.16%, with some organs of higher radiosensitivity including breast, thyroid gland, colon and lungs.