Direct measurement of CTDIw on helical CT scans.

PURPOSE: Medical physics computed tomography (CT) practice involves measurements to determine CTDIvol on representative clinical CT protocols. In current practice the majority of CT exams employ helical scans. To determine CTDIvol for a helical scan, one measures CTDIw with an axial scan, then divides by the pitch. Problems arise in CT units where one is unable to select an axial scan with the same detector configuration and pre-patient (bowtie) filtration that is employed on the helical scan. Presented is a method to measure CTDIw on helical scans. METHODS: The body and head CTDI phantoms were supported on the gantry shroud with brackets attached to the phantom. The phantom is above the tabletop and remains stationary during helical scans as the table moves beneath the phantom. With the phantom stationary, the CTDIw associated with head and body helical scans was measured. CTDIw was also measured for head and body axial scans with the same pre-patient filtrations and detector configurations. RESULTS: For both the head and body CTDI phantom the agreement between the axial and helical CTDIw measurements was <1.5%. CONCLUSIONS: Body and head CTDIw and CTDIvol can be directly measured by employing helical scans with the method in this paper.

STRATEGY OF COMPUTED TOMOGRAPHY IMAGE OPTIMISATION IN CERVICAL VERTEBRAE AND NECK SOFT TISSUE IN EMERGENCY PATIENTS.

INTRODUCTION: With regards to the use of ionisation radiation in the computed tomography (CT), optimal parameters should be used to reduce the risk of incidence of secondary cancers in patients who are constantly exposed to X-rays. The aim of this study was to optimise the parameters used in CT scan of cervical vertebrae and neck soft tissue with minimal loss of image quality in emergency patients. MATERIALS AND METHODS: In this study, the patients were divided into two groups. The first group consisted of patients scanned with default parameters and the second group scanned with optimised parameters. All the study has been implemented in emergency settings. The cases included cervical vertebrae and soft tissue protocols. Common CT dose descriptors including weighted computed tomography dose index (CTDIw), volumetric CTDI (CTDIvol), dose length product (DLP), effective dose (ED) and image noise were measured for each group. The ImpactDose program was used to estimate the organs doses. Statistical analysis was performed using Kruskal-Wallis test using SPSS software. RESULTS: There was no significant quality reduction in the optimised images. Decreasing in radiation dose parameters for the soft tissue was: kVp=16.7%, mAs=64.3% and pitch=24.1%, and for the cervical vertebrae was: kVp=16.7%, mAs=54.2% and pitch=48.3%. Consequently, decreasing these parameters reduced CTDIw=81.0%, CTDIvol=90.0% and DLP = 90.2% in the cervical vertebral protocol, as well as CTDIw=75.5%, CTDIvol=81.3% and DLP = 81.4% in the soft tissue protocol. CONCLUSION: Regarding the results, the optimised parameters in the mentioned organ scan reduce the radiation dose in the target area and the organs surrounding. Therefore, these protocols can be used for reducing the risk of cancer.

Establishment of diagnostic reference levels in computed tomography for select procedures in Pudhuchery, India.

Computed tomography (CT) scanner under operating conditions has become a major source of human exposure to diagnostic X-rays. In this context, weighed CT dose index (CTDIw), volumetric CT dose index (CTDIv), and dose length product (DLP) are important parameter to assess procedures in CT imaging as surrogate dose quantities for patient dose optimization. The current work aims to estimate the existing dose level of CT scanner for head, chest, and abdomen procedures in Pudhuchery in south India and establish dose reference level (DRL) for the region. The study was carried out for six CT scanners in six different radiology departments using 100 mm long pencil ionization chamber and polymethylmethacrylate (PMMA) phantom. From each CT scanner, data pertaining to patient and machine details were collected for 50 head, 50 chest, and 50 abdomen procedures performed over a period of 1 year. The experimental work was carried out using the machine operating parameters used during the procedures. Initially, dose received in the phantom at the center and periphery was measured by five point method. Using these values CTDIw, CTDIv, and DLP were calculated. The DRL is established based on the third quartile value of CTDIv and DLP which is 32 mGy and 925 mGy.cm for head, 12 mGy and 456 mGy.cm for chest, and 16 mGy and 482 mGy.cm for abdomen procedures. These values are well below European Commission Dose Reference Level (EC DRL) and comparable with the third quartile value reported for Tamil Nadu region in India. The present study is the first of its kind to determine the DRL for scanners operating in the Pudhuchery region. Similar studies in other regions of India are necessary in order to establish a National Dose Reference Level.

Comparison of Radiation Dose in the Measurement of MDCT Radiation Dose according to Correction of Temperatures and Pressure, and Calibration of Ionization Chamber / 의학물리

This study aims to conduct the comparative analysis of the radiation dose according to before and after the calibration of the ionization chamber used for measuring radiation dose in the MDCT, as well as of CTDIW according to temperature and pressure correction factors in the CT room. A comparative analysis was conducted based on the measured MDCT (GE light speed plus 4 slice, USA) data using head and body CT dosimetric phantom, and Model 2026C electrometer (RADICAL 2026C, USA) calibrated on March 21, 2007. As a result, the CTDIW value which reflected calibration factors, as well as correction factors of temperature and pressure, was found to be the range of 0.479~3.162 mGy in effective radiation dose than the uncorrected values. Also, under the routine abdomen routine CT image acquisition conditions used in reference hospitals, patient effective dose was measured to indicate the difference of the maximum of 0.7 mSv between before and after the application of such factors. These results imply that the calibration of the ion chamber, and the correction of temperature and pressure of the CT room are crucial in measuring and calculating patient effective dose. Thus, to measure patient radiation dose accurately, the detailed information should be made available regarding not only the temperature and pressure of the CT room, but also the humidity and recombination factor, characteristics of X-ray beam quality, exposure conditions, scan region, and so forth.

Dose Measurements using Phantoms for Tube Voltage, Tube Current, Slice Thickness in MDCT / 의학물리

The purpose of this study was to measure and evaluate radiation dose for MDCT parameters. Patient dose for various combination of MDCT parameters were experimentally measured, using MDCT (GE light speed plus 4 slice, USA), model 2026C electrometer (RADICAL 2026C, USA), standard Polymethylmethacrylate (PMMA) head and body CT dosimetry phantoms. In clinical situations, for a typical abdominal scan performed with MDCT at 120 kVp, 180 mAs, 20 mm collimation, and a pitch of 0.75, CTDIw, CTDIvol were measured as 20.2 mGy, 26.9 mGy, respectively. When scan length is assumed as 271.3 mm, DLP and measured effective dose of the abdominal would be calculated as 729.1 mGy cm, 10.9 mSv, respectively.