Evaluation of Eye Lens Dose Reduction Technics in Head CT

The purpose of this study is to find the best protocol to reduce the X-ray dose to the eye lens during head diagnostic computed tomography (CT) without decreasing image quality in the organs of interest according to the type of scanner. The lens of the eye is one of radiosensitive tissues in the body. Radiation induced cataract has been demonstrated among staff involved in interventional procedures using X-rays. This study compares the absorbed dose and image quality of several dose reduction technics to the eye lens during head CT exam namely bismuth shielding, organ-based dose modulation, tube current modulation, tube voltage modulation and the combination of a number of these techniques. Compared to the reference scan (Fixed tube current without bismuth shielding), the dose to the eye lens was reduced by 29.91% with bismuth shield, 14.55% with tube current modulation, 37.76% with tube current modulation and bismuth shield. The combination of organ-based dose modulation with tube voltage modulation reduced the dose by 44.93% that of tube current modulation with tube voltage modulation reduced by 19.03% and that of tube current modulation with tube voltage modulation and shield by 46.73%. The combination of organ-based dose with tube voltage modulation provided superior image quality than that of tube current modulation with tube voltage modulation and shield while similarly reducing dose to the eye lens.

Variation in tube voltage for pediatric neck 64VCT: Effect on radiation dose and image quality

Exposure to ionizing radiation can cause cancer, especially in children. In computed tomography (CT), a trade-off exists between the radiation dose and image quality. Few studies have investigated the effect of dose reduction on image quality in pediatric neck CT. We aimed to assess the effect of peak kilovoltage on the radiation dose and image quality in pediatric neck multidetector-row CT. Measurements were made using three phantoms representative of children aged 1, 5, and 10 years, with tube voltages of 80, 100, and 120 kilovoltage peak (kVp); tube current of 10, 40, 80, 120, 150, 200, and 250 mA; and exposure time = 0.5 s (pitch, 0.984:1). Radiation dose estimates were derived from the dose-length product with a 64-multidetector-row CT scanner. Images obtained from the control protocol (120 kVp) were compared with the 80- and 100-kVp protocols. The effective dose (ED) was determined for each protocol and compared with the 120-kVp protocol. Quantitative analysis entailed noise measurements by recording the standard deviation of attenuation for a circular 1-cm2 region of interest placed on homogeneous soft tissue structures in the phantom. The mean noise of the various kVp protocols was compared using the unpaired Student t-test. Reduction of ED was 37.58% and 68.58% for neck CT with 100 kVp and 80 kVp, respectively. The image noise level increased with the decrease in peak kilovoltage. Noise values were higher at 80 kVp at all neck levels, but did not increase at 100 kVp, compared to 120 kVp in the three phantoms. The measured noise difference was the greatest at 80 kVp (absolute increases<2.5 HU). The subjective image quality did not differ among the protocols. Thus, reducing voltage from 120 to 80 kVp for neck CT may achieve ED reduction of 68.58%, without compromising image quality.

Analysis and results from a UK national dose audit of paediatric CT examinations

Objectives: To present the results following a UK national patient dose audit of paediatric CT examinations, to propose updated UK national diagnostic reference levels (DRLs) and to analyse current practice to see if any recommendations can be made to assist with optimisation. Methods: A UK national dose audit was undertaken in 2019 focussing on paediatric CT examinations of the head, chest, abdomen/pelvis and cervical spine using the methods proposed by the International Commission on Radiological Protection. The audit pro-forma contained mandatory fields, of which the post-examination dosimetry (CTDIvol and DLP) and the patient weight (for body examinations) were the most important. Results: Analysis of the data submitted indicates that it is appropriate to propose national DRLs for CT head examinations in the 0- < 1, 1- < 5, 5- < 10 and 10- < 15 year age ranges. This extends the number of age categories of national DRLs from those at present and revises the existing values downwards. For CT chest examinations, it is appropriate to propose national DRLs for the first time in the UK for the 5- < 15, 15- < 30, 30- < 50 and 50- < 80 kg weight ranges. There were insufficient data received to propose national DRLs for abdomen/pelvis or cervical spine examinations. Recommendations towards optimisation focus on the use of tube current (mA) modulation, iterative reconstruction and the selection of examination tube voltage (kVp). Conclusions: Updated UK national DRLs are proposed for paediatric CT examinations of the head and chest. Advances in knowledge: A national patient dose audit of paediatric CT examinations has led to the proposal of updated national DRLs.

Studies on the radiation dose, image quality and low contrast detectability from MSCT abdomen by using low tube voltage

Background To study radiation dose, image quality and low-contrast cylinder detectability from multislice CT (MSCT) abdomen by using low tube voltage using the American College of Radiology (ACR) phantom. The ACR phantom (low-contrast module) was scanned with 64 MSCT scanner (Brilliance, Philips Medical System, Eindhoven, Netherlands) with 80 and 120 KVP, utilizing different tube current time product (mAs) range from 50 to 380 mAs. The image noise (SD), signal to noise ratio, contrast-to-noise ratio (CNR), and scores of low contrast detectability were assessed for every image respectively. Results From images analyses, the noise essentially increased with the use of low tube voltage. The CNR was 0.94 ± 0.27 at 120 KVP, and CNR was 0.43 ± 0.22 at 80 KVP. However, with the same dose, there were no differences of statistical significance in scores of low-contrast detectability between 120 KVP at 300mAs and 80 KVP at (200–380) mAs (p > 0.05). At 300 mAs, the CTDIvol obtained at 80 KVP was about 29% of that at 120 KVP. The CTDIvol obtained at 80 KVP were decreased from 5% at 50 mAs, to 37% at 380 mAs. Conclusions There is a possibility to decrease exposure of radiation virtually by reducing KVP from 120 to 80 KVP in examination of abdominal CT when the high tube current is used, though increasing image noise at low tube voltage.

Impacts of Phantom Off-Center Positioning on CT Numbers and Dose Index CTDIv: An Evaluation of Two CT Scanners from GE

The purpose of this work is to evaluate the impacts of body off-center positioning on CT numbers and dose index CTDIv of two scanners from GE. HD750 and APEX scanners were used to acquire a PBU60 phantom of Kagaku and a 062M phantom of CIRS respectively. CT images were acquired at various off-center positions under automatic tube current modulation using various peak voltages. CTDIv were recorded for each of the acquisitions. An abdomen section of the PBU60 phantom was used for CT number analysis and tissue inserts of the 062M phantom were filled with water balloons to mimic the human abdomen. CT numbers of central regions of interests were averaged using the Fiji software. As phantoms were lifted above the iso-center, both CTDIv and CT numbers were increased for the HD750 scanner whilst they were approximately constant for the APEX scanner. The measured sizes of anterior-posterior projection images were also increased for both scanners whilst the sizes of lateral projection images were increased for the HD750 scanner but decreased for the APEX scanner. Off-center correction algorithms were implemented in the APEX scanner. Matching the X-ray projection center with the system’s iso-center could improve the accuracy of CT imaging.

Filament X-ray Tube Current Control Method Using Indirect Filament Temperature Estimation

The recent increase in ailments has increased the demand for diagnosis and surgery based on X-rays. An X-ray system using a filament-type tube heats the filament for operation, and the electrons emitted by the thermal energy during this process produce X-rays. Conventionally, current control-based methods are used to regulate heating. However, these methods do not control the temperature of the filament, resulting in lower or higher output than the desired dose rate. Therefore, we propose a filament temperature control method that enables constant temperature control, which cannot be achieved using the existing heating method for X-ray systems with filament tubes. Additionally, we developed an indirect temperature estimation algorithm for the tungsten filament to incorporate the proposed method. To validate the tube current control through temperature control, we performed experiments to compare the existing current-controlled heating and temperature control methods in terms of the filament temperature. As the tube current is proportional to the dose rate, it was measured through a comparative analysis of the change in the output of dose rate over time. The obtained results validate that the proposed method can maintain both the filament temperature and tube current at the desired level.

Use of Multi-Modality Technology to Reduce the Radiation Dose of Multi-Slice Spiral CT Coronary Angiography (MSCTCA) in Normal Weight and Overweight Patients

Purpose: This study was performed to explore the value of multi-modality technology, with a combination of narrow acquisition window, isocentric scanning, low tube voltage, low tube current and iterative reconstruction (IR), for reducing the radiation dose in multi-slice spiral computed tomography coronary angiography (MSCTCA). Materials and methods: In this prospective randomised controlled study, 154 patients with coronary heart disease (CHD) were classified according to body mass index (BMI) as normal weight (BMI 18–27kg/m2) or overweight (BMI ≥ 27 kg/m2), and divided into four groups: multi-modality–normal BMI group (A1, n = 82); multi-modality–overweight group (B1, n = 17); conventional–normal BMI group (A2, n = 39); and conventional–overweight group (B2, n = 16). The parameters in the multi-modality groups were as follows: isocentric scan, tube voltage = 80 kV, tube current control using 80% “smart milliampere”, and maximum current during 60–80% of the RR interval. The parameters in the conventional groups were as follows: normal position, tube voltage = 100 kV, tube current control using smart milliampere, and maximum current during 30–80% of the RR interval. The effective radiation dose (ED), objective image quality (IQ), noise, signal-to-noise ratio (SNR), contrast signal-to-noise ratio (CNR) and subjective 5-point Likert scale IQ scores of MSCTCA images were compared among the four groups. Results: The average EDs of groups A1, A2, B1and B2 were( 1.13±0.35 ) mSv, ( 3.36±1.30 ) mSv, ( 1.54±0.53 ) mSv and ( 5.90±0.93 ) mSv, respectively. There were statistically significant differences in ED between groups A1 and A2, and between groups B1 and B2 (all P < 0.01). Noise was significantly lower, and both SNR and CNR were significantly higher, in group A2 than group A1 (all P < 0.01), but there were no significant differences in these parameters between groups B1 and B2 (P = 0.14–0.51). The average IQ scores of groups A1, A2, B1and B2 were 4.46±0.59(Fig.3), 4.45±0.62(Fig.4), 4.39±0.68(Fig.5) and 4.42±0.66(Fig.6),respectively. There were no significant differences in subjective IQ scores among the four groups (P = 0.12). Consistency among observers in the subjective IQ scores of the four groups was very good, with intraclass correlation coefficients (ICCs) of 0.71–0.90. The subjective IQ scores of the coronary artery were excellent in all four groups, with a total good-to-excellent rate of ≥ 92.64%, and the total number of evaluable segments in the images of all four groups was ≥ 98.26%. Conclusions: Under conditions appropriate for clinical diagnosis, multi-modality technology can reduce the radiation dose of MSCTCA scans in both normal weight and overweight patients.

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.