CT doses based on clinical indications. New national DRL's in Iceland.

A diagnostic reference level (DRL) is an investigation level to use in the optimization of a medical exposure using ionizing radiation. The aim of this project was to gather dose data from computed tomography (CT) studies in Iceland with the purpose of updating existing national DRL and proposing DRLs based on clinical indications. Dose data (total dose length product (DLP) and CT dose index) were retrospectively collected from all CT scanners in Iceland for 50 patients for all common CT studies. After cleaning the data, the data set contained total DLP for 8129 patients. Considering dose-relevant parameters such as the number of phases and scan length, each CT study was assigned to one of 42 study types and (at least) one clinical indication. Data were received from seven or more scanners for 13 clinical indications and from all scanners providing coronary angiography. There was considerable variation in the median total DLP from different scanners, e.g., from 13 to 139 mGycm for Sinusitis, and, the range of individual total DLPs varied between scanners. This underscores the importance of monitoring patients' exposure. The study shows that there is room for optimization. New Icelandic NDRLs were proposed for the total DLP of CT examinations based on ten different indications, including: Brain ischemia (1060 mGycm), Interstitial lung disease (310 mGycm) and Appendicitis (690 mGycm). The proposed NDRLs were the first clinical indication based NDRLs in Iceland. The Icelandic Radiation Safety Authority has decided to update the NDRLs based on the results of this study.

Paediatric diagnostic reference levels for common radiological examinations using the European guidelines.

OBJECTIVE: The purpose of this study was to explore the feasibility to determine regional diagnostic reference levels (RDRLs) for paediatric conventional and CT examinations using the European guidelines and to compare RDRLs derived from weight and age groups, respectively. METHODS: Data were collected from 31 hospitals in 4 countries, for 7 examination types for a total of 2978 patients. RDRLs were derived for each weight and age group, respectively, when the total number of patients exceeded 15. RESULTS: It was possible to derive RDRLs for most, but not all, weight-based and age-based groups for the seven examinations. The result using weight-based and age-based groups differed substantially. The RDRLs were lower than or equal to the European and recently published national DRLs. CONCLUSION: It is feasible to derive RDRLs. However, a thorough review of the clinical indications and methodologies has to be performed previous to data collection. This study does not support the notion that DRLs derived using age and weight groups are exchangeable. ADVANCES IN KNOWLEDGE: Paediatric DRLs should be derived using weight-based groups with access to the actual weight of the patients. DRLs developed using weight differ markedly from those developed with the use of age. There is still a need to harmonize the method to derive solid DRLs for paediatric radiological examinations.

Establishing paediatric diagnostic reference levels using reference curves - A feasibility study including conventional and CT examinations.

PURPOSE: To derive Regional Diagnostic Reference Levels (RDRL) for paediatric conventional and CT examinations using weight-based DRL curves and compare the outcome with DRL derived using the weight groups. METHODS: Data from 1722 examinations performed at 29 hospitals in four countries were included. DRL was derived for four conventional x-ray (chest, abdomen, pelvis, hips/joints) and two types of CT examinations (thorax, abdomen). DRL curves were derived using an exponential fit to the data using weight as an independent variable and the respective radiation dose indices (PKA, CTDIvol, DLP) as dependent variables. DRL was also derived for weight groups for comparison. The result was compared with national diagnostic reference level (NDRL) curves. RESULTS: The derived curves show similarities with the NDRL curves available and corresponded sufficiently well with DRL for weight groups using the same data set, if sufficient number of data was available. CONCLUSIONS: We conclude that weight-based DRL curves are a feasible approach and could be used together with DRL for weight groups. The main advantage of DRL curves is its application in the clinic. When the examination frequency is low, time to collect enough data to establish typical values for one or several weight groups may be unreasonably long. The curve provides the means to compare dose level faster and with fewer data points.

[Effective dose from pediatric CT in Iceland].

INTRODUCTION: It is important to know the effective dose from computed tomography (CT) examinations. The aim of this study was to evaluate the effective dose from pediatric CT examinations in Iceland. MATERIALS AND METHOD: For all pediatric CT exams (children < 18 years) performed during one year (1.2.2016 till 1.2.2017), data on age, examination type and dose length product was retrospectively collected from the Landspitali University Hospital's archives, as was the total number of CT examinations. The ratio of pediatric CT exams and the frequency of examination types were calculated and, for the three most common examinations, the effective dose and mean dose length product were calculated for five age groups. RESULTS: The total number of pediatric CT examinations was 662, 3,6% of all the CT examinations performed. The three most common pediatric CT examinations were head (40,3%), abdomen (15,6%) and thorax (10,3%). The mean effective dose in those was, in the above order: for children < 4 months: 5,3/4,9/3,0 mSv; 4 months to < 3 years: 4,2/5,5/1,9 mSv; 3 years to < 8 years: 2,7/ 3,4/1,0 mSv; 8 years to < 15 years: 3,2/4,4/1,0 mSv and 15 years to < 18 years: 2,1/6,5/3,3 mSv. The mean dose length product was above European diagnostic reference levels in most examination types and age groups. CONCLUSION: Possibilities for lower effective doses from pediatric CT examinations should be explored. For that purpose, the use of size specific dose estimates is recommended.

[Effect of coronary calcification on diagnostic accuracy of the 64 row computed tomography coronary angiography]. / Ahrif kalks i kransaedum a greiningargildi TS-kransaedarannsoknar.

INTRODUCTION: Coronary artery calcium is known to complicate the evaluation of stenoses using computer tomography (CT). The aim of this study was to analyze the effect of coronary calcification on the diagnostic accuracy of CT coronary angiography in an Icelandic population. MATERIAL AND METHODS: The study was a retrospective analysis of 417 consecutive subjects that underwent CT coronary angiography and subsequent conventional coronary angiography within 6 months. Subjects were divided based on total Agatston score: 0, 0.1-10, 10.1-100, 100.1-400, 400.1-750 and >750. Sensitivity, specificity, positive and negative predictive values were calculated for ≥50% stenoses diagnosed with the CT, using the conventional coronary angiography as a reference. Correlation between Agatston score and ≥50% stenoses was calculated. RESULTS: A total of 1668 coronary artery segments in 417 individuals were evaluated (68.6% men, mean age 60.2 ± 8.9). The total mean Agatston score was 420 (range from 0-4275). CT detected >50% stenoses with a sensitivity of 70.1%, specificity of 79.9% and positive and negative predictive values of 55.4% and 88.2%, respectively. The negative predictive value was 93.0% for Agatston score zero but 78.3% for Agatston score ˃750. An Agatston score threshold of 363 predicted ≥50% coronary stenoses with 49.6% sensitivity. CONCLUSION: Diagnostic accuracy is moderate with good negtive predictive value and specificity. Although coronary calcification reduces diagnostic accuracy, negative predictive value is only mildly affected for Agatston score as high as 400. Agatston score is not a good predictor of ≥50% coronary artery stenoses. No particular Agatston score cut-off level was identified to indicate whether CT angiography was useless or not.

Optimal use of AEC in CT: a literature review.

BACKGROUND: Computed tomography (CT) examinations account for a significant portion of individuals' increasing exposure to medical radiation. Automatic exposure control (AEC) was introduced in CT scanners to decrease patient doses while maintaining appropriate image quality. OBJECTIVE: To identify areas for AEC optimization and suggest practical optimization methods. METHODS: A literature review was conducted to assess current knowledge regarding tube current modulation and AEC in CT from peer-reviewed journals and publications from national and international organizations involved in medical imaging and radiation protection. RESULTS: Four important aspects of AEC use were identified: interaction of user-selectable parameters with AEC, patient positioning and AEC, specific challenges with patient size groups and how to select appropriate input value. CONCLUSION: AEC is a useful tool for dose optimization but dose savings are not guaranteed unless the equipment is used properly. Further research is required into optimal use of AEC, particularly for pediatric examinations.

Diagnostic accuracy of 64-slice multidetector CT for detection of in-stent restenosis in an unselected, consecutive patient population.

OBJECTIVES: To investigate the diagnostic accuracy of 64-slice multidetector computed tomography (64-CT) for detection of in-stent restenosis (ISR) in an unselected, consecutive patient population. BACKGROUND: Detection of in-stent restenosis by cardiac CT would be a major advance for the evaluation of patients suspected of having ISR. However, the diagnostic accuracy of current generation 64-CT in this context is not fully established. METHODS: We conducted a prospective study on patients with stable angina or acute coronary syndrome with no prior history of coronary artery disease. Six months after percutaneous coronary intervention (PCI) with stent placement they underwent a 64-CT scan (Toshiba Multi-Slice Aquilion 64) and consequently a repeat coronary angiography for comparison. Cardiac CT data sets were analyzed for the presence of in-stent restenosis by two independent expert readers blinded to the coronary angiographic data. RESULTS: Ninety-three patients with a total of 140 stents were evaluated. Males comprised 82% of the study group and the mean age was 63±10 years. The mean time from PCI to the repeat coronary angiography was 208±37 days and the mean time from 64-CT to repeat coronary angiography was 3.7±4.9 days. The restenosis rate according to coronary angiography was 26%. Stent diameter, strut thickness, heart rate and body mass index (BMI) significantly affected image quality. The sensitivity, specificity, positive and negative predictive values of 64-CT for detection of in-stent restenosis were 27%, 95%, 67% and 78%, respectively. CONCLUSIONS: Current generation, 64-slice CT, remains limited in its ability to accurately detect in-stent restenosis.

[Diagnostic accuracy of 64-slice computed tomography compared with coronary angiography]. / Greiningarhaefni 64 sneida tövusneidmyndataekni til samanburdar vid hefdbundna kransaedapraedingu.

OBJECTIVE: The aim of this study was to evaluate the diagnostic accuracy (sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV)) of 64-slice multidetector computed tomography (MDCT) compared with quantitative coronary angiography (QCA) for detection of coronary artery disease (CAD). MATERIAL AND METHODS: Sixty-nine patients participating in a study of coronary in-stent restenosis were investigated. After a 64-slice MDCT scan patients were evaluated by QCA. The coronary arteries were divided into 15 segments and stenosis was graded for each segment by both methods. The diagnostic accuracy of 64-slice MDCT was evaluated using the QCA as the gold standard. RESULTS: Among the 69 patients included in the study 13 (19%) were female and 56 male. The mean age was 63 (SD 10) years. The following risk factors were present: high blood pressure 67%, elevated blood cholesterol 54%, diabetes 12% and family history of CAD 71%. Current smokers were 22% and previous smokers were 48%. Altogether 663 segments were examined. Of those 221 (33%) segments were excluded; 103 because of stents, 48 because of heavy calcification, 41 because of motion artifacts and 29 because the segments were less than 1.5 mm in diameter. The mean time between MDCT and QCA was 6.3 (SD 12.1) days. The sensitivity of 64-slice MDCT for diagnosing significant stenosis (>or= 50% according to QCA) was 20%, the specificity was 94%, PPV was 16%, NPV was 95% and the accuracy was 89%. CONCLUSION: High NPV and specificity indicates that MDCT is useful for accurately excluding significant CAD but the low sensitivity and low PPV indicate that the method is not accurate in diagnosing coronary artery stenosis of 50% or more according to QCA.