RADIATION DOSE TO THE EYE AND POTENTIAL OCCURRENCE RADIATION- INDUCED CATARACT FOLLOWING COMPUTED TOMOGRAPHY (CT) HEAD EXAMINATION

The eye is a radiosensitive organ that lies within the scan range during Computed Tomography (CT) of the head. The utilization of the head CT is increasing with growing concern about the chances of development of cataract which induces by ionising radiation. This research aimed to calculate eye absorbed dose and to study the potential occurrence of radiation induces cataracts between CT Brain and CT Temporal. A total of 399 set data were obtained retrospectively according to inclusion and exclusion criteria. 364 patients underwent CT Brain while 35 patients’ data obtained for CT Temporal. The scanning parameters such as tube current, tube potential, pitch factor, beamwidth, filter, revolution time, and filter were recorded. Eye absorbed dose was significantly different (p<0.05) between CT brain (49.07±10.08mGy) and CT temporal (25.72 ± 6.12mGy). None of the analysed data exceeded the eye threshold dose recommended by ICRP 2012. However, as expected, the cumulative eye absorbed dose was increased as the frequencies of the scan increase. The highest number of repeated scans is five times with cumulative dose was recorded as 278.27mGy. In conclusion, the eye absorbed dose is higher in CT Brain compared to CT Temporal and has potential for induction of cataract in the future especially with the patient that undergoes repeated CT examination.

Effect of Lowering Tube Potential and Increase Iodine Concentration of Contrast Medium on Radiation Dose and Image Quality in Computed Tomography Pulmonary Angiography Procedure: A Phantom Study

The aim of the study was to examine the effect of lowering tube potential and increase iodine concentration on image quality and radiation dose in computed tomography pulmonary angiography procedure. The pulmonary arteries were simulated by three syringes. The syringes were filled with 1:10 diluted solutions of 300 mg, 350 mg and 370 mg of iodine per millilitre concentration in three water-filled phantoms simulating thin, intermediate and thick patients. The phantoms were scanned at 80 kVp, 110 kVp and 130 kVp and 0.6 second rotation time using a 16 slice computed tomography (CT) scanner. The tube current was either fixed at 80, 100, 200, 250 and 300 mA or automatically adjusted with quality reference tube current-time product (mAsQR). In comparison with 130 kVp, images acquired at 80 kVp and 110 kVp, respectively, showed 76.2% to 99% and 19% to 26% enhancement in CT attenuation of iodinated contrast material. A volume CT dose index (CTDIvol) reduction by 35.3% was attained in small phantom with the use of 80 kVp, while in the medium phantom, a CTDIvol reduction by 29.9% was attained with the use of 110 kVp instead of 130 kVp. In light of the above, lowering tube potential and increase iodinated CM could substantially reduce the dose to small-sized adults and children. Keywords: Angiography; Computed tomography; Low tube potential; Iodinated contrast medium; Radiation dose

Impact of iodine concentration and scan parameters on image quality, contrast enhancement and radiation dose in thoracic CT

Background We investigated the impact of varying contrast medium (CM) densities and x-ray tube potentials on contrast enhancement (CE), image quality and radiation dose in thoracic computed tomography (CT) using two different scanning techniques. Methods Seven plastic tubes containing seven different CM densities ranging from of 0 to 600 HU were positioned inside a commercial chest phantom with padding, representing three different patient sizes. Helical scans of the phantom in single-source mode were obtained with varying tube potentials from 70 to 140 kVp. A constant volume CT dose index (CTDIvol) depending on phantom size and automatic dose modulation was tested. CE (HU) and image quality (contrast-to-noise ratio, CNR) were measured for all combinations of CM density and tube potential. A reference threshold of CE and kVp was defined as ≥ 200 HU and 120 kVp. Results For the medium-sized phantom, with a specific CE of 100–600 HU, the diagnostic CE (200 HU) at 70 kVp was ~ 90% higher than at 120 kVp, for both scan techniques (p < 0.001). Changes in CM density/specific HU together with lower kVp resulted in significantly higher CE and CNR (p < 0.001). When changing only the kVp, no statistically significant differences were observed in CE or CNR (p ≥ 0.094), using both dose modulation and constant CTDIvol. Conclusions For thoracic CT, diagnostic CE (≥ 200 HU) and maintained CNR were achieved by using lower CM density in combination with lower tube potential (< 120 kVp), independently of phantom size.