Digital radiography image quality evaluation using various phantoms and software.

PURPOSE: To investigate the effect of the exposure parameters on image quality (IQ) metrics of phantom images, obtained automatically using software or from visual evaluation. METHODS: Three commercial phantoms and a homemade phantom constructed according to the instructions given in the IAEA Human Health Series No. 39 publication were used, along with the respective software that estimate automatically various IQ metrics. Images with various exposure parameters were acquired in a digital radiography (DR) unit. For the commercial phantoms, visual evaluations were also performed. The IQ scores obtained were analyzed to investigate the effects of increasing incident air kerma (IAK), tube potential (kVp), additional filtration, and acquisition protocol on IQ. RESULTS: The effects of the exposure parameters on the IQ metrics, determined with the commercial and the IAEA phantoms, were not the same. For example, clear trends of improvement of IQ scores with increased IAK and reduction of most IQ scores with increased kVp were observed mostly with the IAEA phantom, but not with the commercial phantoms (for both automatic and visual scoring methods). For all phantoms, the maximum variations in IQ scores observed for repeated identical exposures were almost always below 10% with automatic evaluation whereas, for visual evaluation, reached 17%. CONCLUSIONS: Failure to detect some expected trends with the complex commercial phantoms may be attributed to the fact that IQ in DR is more strongly affected by the post-processing procedures, which may mask the effect of other parameters on IQ, something that was not observed with the simple IAEA phantom.

Evaluation of automatic tube current modulation of CT scanners using a dedicated and the CTDI dosimetry phantoms.

PURPOSE: To investigate the operation principles of the automatic tube current modulation (ATCM) of a CT scanner, using a dedicated phantom and the CT dosimetry index (CTDI) phantom. MATERIAL AND METHODS: The Mercury 4.0 phantom and three different configurations of the CTDI dosimetry phantom were employed. A frequently used clinical scanning protocol was employed as a basis for the acquisitions performed with all phantoms, using both scanning directions. Additional acquisitions with different pitch and examination protocols were performed with Mercury phantom, to further explore their effect on ATCM and the resulting image quality. Different software named DICOM Info Extractor, ImageJ, and imQuest, were used to derive CTDIvol and table position, image noise, and water equivalent diameter (WED) of each phantom CT image, respectively. ImQuest was also used to derive the detectability index (d') of five different materials (air, solid water, polystyrene, iodine, and bone) embedded in the Mercury phantom. RESULTS: It was exhibited with all four phantoms that the scanning direction greatly affects the modulation curves. The fitting of the dose modulations curves suggested that for each table position what determines the CTDIvol value is the WED values of the phantom structures laying ahead towards the scanning direction, for a length equal to the effective width of the X-ray beam. Furthermore, it was also exhibited that ATCM does not fully compensate for larger thicknesses, since images of larger WED phantom sections present more noise (larger SD) in all four phantoms and in Mercury 4.0 phantom smaller detectability (d'). CONCLUSION: Mercury 4.0 is a dedicated phantom for a complete and in-depth evaluation of the ATCM operation and the resulting image quality. However, in its absence, different CTDI configurations can be used as an alternative to investigate and comprehend some basic operation principles of the CT scanners' ATCM systems.

Development of image quality related reference doses called acceptable quality doses (AQD) in paediatric CT exams in Qatar.

OBJECTIVES: To describe first experience of integrating assessment of image quality in paediatric X-ray computed tomography (CT) with analysis of the radiation dose indices to develop reference doses called acceptable quality dose (AQD). METHODS: Image quality was scored by the radiologists at a tertiary care hospital in Qatar on a scale of 0 to 4 using the recently published scoring criteria. The patients undergoing head, chest and abdomen CT were divided in different weight groups as follows: < 5 kg, 5-< 15 kg, 15-< 30 kg, 30-< 50 kg, 50-< 80 kg and > 80 kg. The images that were clinically acceptable (score of 3) were included for assessment of median values of CTDIvol and DLP to obtain AQDs in different weight groups. RESULTS: After initial training in image quality scoring of CT images of 49 patients by three radiologists, the study on 715 patients indicated 665 studies (93%) were clinically acceptable as per scoring criteria. The median CTDIvol values for the above weight groups were 16, 20, 22, 22, 27 and 27 mGy and the median DLP values for these weight groups were 271, 377, 463, 486, 568 and 570 mGy cm, respectively, for head CT. Similar values are presented for chest and abdomen CTs. CONCLUSIONS: The first ever experience of starting with image quality assessment and integrating it with analysis of dose indices to obtain AQD values shall provide a workable model for others and values for comparison within the facility and in other facilities leading to optimisation. KEY POINTS: • The first study to integrate image quality assessment with analysis of patient dose indices shows feasibility for routine practice in other centres. • The values of acceptable quality dose (AQD) were provided for head, chest and abdomen CT of children divided into weight groups rather than age. They shall act as reference values for future studies. • Verification of our findings on proportional increase in exposure parameters (CTDIvol and DLP) with weight by other investigators shall be helpful.

Patient exposure during videofluoroscopic swallowing studies performed by speech-language pathologists.

Videofluoroscopic swallowing studies (VFSSs) are fluoroscopic examinations performed by speech and language pathologists (SLPs), for the evaluation of the oral and pharyngeal phases of swallowing, in patients who are diagnosed with symptoms like dysphagia and speech impairment. The study was focused on the evaluation of the patient doses from VFSS performed at Hamad Medical Corporation hospitals. Data on the patient exposure and examination parameters were extracted from the Radiation Dose Monitoring system, statistically analysed and compared with literature. For adult patients, the mean (median) values for fluoroscopy time and kerma-air product were 2.8 (2.7) min and 181 (144) cGycm2, respectively. For children, the respective mean (median) values were 2.6 (2.4) min and 15.3 (9.2) cGycm2. The results of the study indicate that the VFSS are performed by well-trained health professionals, and as a result, image quality sufficient for a confident diagnosis is obtained at relatively low dose levels.

From the use of exposure index in quality control testing to the use of exposure index for quality control of clinical images.

Aim: The exposure index (EI) is used in routine quality control (QC) tests performed in the radiographic equipment installed in our hospitals. This study aimed at investigating the factors affecting the calculation of EI in QC and clinical images, and the implementation of target EI (EIT) and deviation index (DI) in clinical practice. Methods: The EI is 100 times the incident air kerma (IAK) in µGy on the image receptor, using the RQA-5 X-ray beam quality. Conformance to this relationship was investigated in QC images and clinical images acquired using anthropomorphic phantom body parts and different examination protocols, tube potential settings and radiation field sizes. Furthermore, a survey on EIT and DI data from clinical images was performed. Results: Though automatic exposure control (AEC) systems have been adjusted for an IAK of 2.5 µGy, for most anthropomorphic phantom images the EIs were far from 250, depending on the manufacturer, the anatomy imaged, and the examination protocol. Regarding the survey results, DI calculation was feasible in only 38 % of the systems, since for the rest EIT values have not been set. However, the rationale based on which EIT have been selected is unclear. Some systems use only one while others many different EIT values. Conclusion: Before using EI for quality control of clinical images image all receptors and AEC systems should be properly calibrated. Then, the methodology of selecting appropriate EIT should be refined, since the EI calculation may vary, depending on the manufacturer, the anatomy imaged, and the examination protocol.

Towards establishment of diagnostic reference levels based on clinical indication in the state of Qatar.

OBJECTIVES: The objectives of this study were to: 1) evaluate patient radiation exposure in CT and 2) establish CT Diagnostic Reference Levels (DRL)s based on clinical indication (CI) in Qatar. MATERIALS AND METHODS: Patient data for 13 CIs were collected using specially designed collection forms from the dose management software (DMS) of Hamad Medical Corporation (HMC), the main Qatar healthcare provider. The methodology described in the International Commission on Radiological Protection (ICRP) Report 135 was followed to establish national clinical DRLs in terms of Volumetric Computed Tomography Dose Index (CTDIvol) and total Dose Length Product (DLPt). Effective dose (Ef) was estimated by DMS using DLPt and appropriate conversion factors and was analyzed for comparison purposes. RESULTS: Data were retrospectively collected for 896 adult patients undergoing CT examinations in 4 hospitals and 7 CT scanners. CT for Diffuse infiltrative lung disease imparted the lowest radiation in terms of CTDIvol (5 mGy), DLPt (181 mGy.cm) and Ef (3.6 mSv). Total body CT for severe trauma imparted the highest DLPt (3137 mGy.cm) and Ef (38.6 mSv) of all CIs with a CTDIvol of 15 mGy. Rounded Third quartile CTDIvol and DLPt values were defined as the Qatar CT clinical DRLs. Comparison was limited due to sparse international literature. When this was possible data were lower or comparable with other studies. CONCLUSIONS: This is the first study reporting national clinical DRLs in Asia and second one internationally after UK. For accurate comparison between studies, systemized CI nomenclature must be followed by researchers.

EVALUATION OF RADIATION DOSE FOR PATIENTS UNDERGOING MAMMOGRAPHY IN QATAR.

In the absence of information on radiation doses in mammography in the Gulf countries, this study was designed to assess patient dose in terms of entrance surface air kerma and average glandular dose (AGD) in three mammography units in Qatar that covers 21% of all mammography systems in the country. The study of 150 patients involving 600 projections indicated that the average value of AGD in patients was 2.2 mGy for cranio-caudal and 2.5 mGy for mediolateral-oblique views, respectively. Dose assessment was also performed for polymethyl methacrylate phantoms of thicknesses, ranging from 20 to 80 mm. Comparing the patient dose values with several other publications in literature for full-field digital mammography, our values are typically higher, which can be likely attributed to the larger compressed breast thickness.