Individually weight-adapted examination protocol in retrospectively ECG-gated MSCT of the heart

The standard protocol in multislice spiral CT (MSCT) angiography for coronary arteries with fixed tube current-time settings leads to an overexposure and thus to an unnecessary high radiation dose in patients with lower weight when compared to heavier patients. The purpose of this study was to estimate the effect of reducing the radiation dose by adapting the tube current-time settings individually. Fifty patients underwent retrospectively ECG-gated MSCT of the heart. In 25 patients (group A₁) a standard protocol with constant tube current-time settings was used (4×1-mm collimation, 120 kV, 400 mAs_eff). Subsequently, artificial image noise was added to the data of these patients simulating a directive for weight-adapted tube current-time settings (group A₂). In the other 25 patients (group B) an alternative protocol with individually weight-adapted tube current-time settings was applied. The data of all groups were evaluated by a regression analysis. The image quality was assessed objectively by measuring the CT attenuation in standardised regions of interest and subjectively by three radiologists using a five-point scoring system in a consensus reading. Applying the weight-adapted tube current-time settings the effective radiation dose was reduced by 17.9% for men and 26.3% for women. The standard protocol leads to an overexposure in light patients as seen in the plot of noise vs weight (slope 0.16±0.07 HU/kg). By applying the weight-adapted tube current-time settings a weight-independent, constant image noise is achieved (slope 0.04±0.1 HU/kg). Diagnostic image quality was preserved in all patients. Individually weight-adapted tube current-time settings allow for a substantial dose reduction when performing retrospectively ECG-gated MSCT angiography for coronary arteries without impairment of diagnostic image quality.     

The accuracy of 1- and 3-mm slices in coronary calcium scoring using multi-slice CT in vitro and in vivo

The accuracy of coronary calcium scoring using 16-row MSCT comparing 1- and 3-mm slices was assessed. A thorax phantom with calcium cylinder inserts was scanned applying a non-enhanced retrospectively ECG-gated examination protocol: collimation 12×0.75 mm; 120 kV; 133 mAs_eff. Thirty-eight patients were examined using the same scan protocol. Image reconstruction was performed with an effective slice thickness of 3 and 1 mm. The volume score, calcium mass and Agatston score were determined. Image noise was measured in both studies. The volume score and calcium mass varied less than the Agatston score. The overall measured calcium mass compared to the actual calcium mass revealed a relative difference of +2.0% for 1-mm slices and −1.2% for 3-mm slices. Due to increased image noise in thinner slices in the patient study (26.1 HU), overall calcium scoring with a scoring threshold of 130 HU was not feasible. Interlesion comparison showed significantly higher scoring results for thinner slices (all P<0.001). A similar accuracy comparing calcium scoring results of 1- and 3-mm slices was shown in the phantom study; therefore, the potentially necessary increase of the patient's dose in order to achieve assessable 1-mm slices with an acceptable image-to-noise-ratio appears not to be justified. The study was supported by a “START” grant from the University Hospital of Aachen, Germany.     

64-Slice spiral computed tomography of the coronary arteries: dose reduction using an optimized imaging protocol including individual weight-adaptation of voltage and current–time product

Radiation dose and image quality were compared between a standard protocol (40 patients, group A) and a weight-adapted protocol of voltage and current–time product (44 patients, group B) using 64-slice coronary multidetector computed tomography (MDCT). Effective dose estimate was lower by 37% in all patients of group B (9.2 ± 2.5 mSv) compared with group A (14.6 ± 2.3 mSv, P < 0.0001). Group B patients with a small body mass index (BMI) benefited most with a dose reduction of 53% (6.7 ± 1.5 mSv in group B versus 14.1 ± 1.8 mSv in group A, P < 0.0001). Moderate reductions of 32% and 20% were achieved for patients with a medium and large BMI, respectively. Reduction in radiation dose did not affect the image quality as assessed by image noise, signal-to-noise ratios, and number of coronary segments with good diagnostic image quality. Individual weight-adaptation of voltage and current–time product significantly reduces the radiation dose without loss of image quality.     

Prospective respiratory-triggered 64-slice CT pulmonary angiography for detection of pulmonary embolism—a feasibility study in a porcine model

The objective of this study is to investigate the feasibility of prospectively respiratory-triggered CT pulmonary angiography (CTPA) for detection of pulmonary embolism (PE) in a porcine model. A free-breathing respiratory-triggered multislice CTPA (120 kV, 140 mAs_eff, 2.5-mm slice thickness) and two CTPA in breath-hold technique (120 kV, 140 mAs_eff. and 250mAs_eff, 1-mm and 3-mm image reconstruction) were performed in six pigs with pulmonary embolism. Diagnostic accuracy was computed, and differences in detection rates between both techniques were assessed on a per-embolus basis with the Wilcoxon test. Thin-sliced 1-mm images, acquired with 250mAs_eff, served as the standard of reference. Respiratory-triggered CTPA reached high diagnostic accuracy in detection of lobar and segmental PE equal to the results with the breath-hold technique (p > 0.05). For detection of subsegmental emboli, standard breath-hold techniques performed significantly better than respiratory-gated CTPA (sensitivity, 68.3% versus 24.4%; p < 0.05). Free-breathing respiratory-triggered CTPA is feasible for detection of lobar and segmental PE, with diagnostic accuracy equivalent to that of a standard CTPA in breath-hold. Although this technique is not recommended for assessment of emboli in the subsegmental vasculature, prospective respiratory-triggered CTPA may be of added value in patients who cannot hold their breath appropriately for CTPA scanning.     

Multidetector computed tomography (MDCT) evaluation of myocardial viability: intraindividual comparison of monomeric vs. dimeric contrast media in a rabbit model

To evaluate the influence of different types of iodinated contrast media on the assessment of myocardial viability, acute myocardial infarction (MI) was surgically induced in six rabbits. Over a period of 45 min, contrast-enhanced cardiac MDCT (64 × 0.6 mm, 80 kV, 680mAs_eff.) was repeatedly performed using a contrast medium dose of 600 mg iodine/kg body weight. Animals received randomized iopromide 300 and iodixanol 320, respectively. Attenuation values of healthy and infarcted myocardium were measured. The size of MI was computed and compared with nitroblue tetrazolium (NBT)-stained specimen. The highest attenuation differences between infarcted and healthy myocardium occurred during the arterial phase with 140.0 ± 3.5 HU and 141.0 ± 2.2 HU for iopromide and iodixanol, respectively. For iodixanol the highest attenuation difference on delayed contrast-enhanced images was achieved 3 min post injection (73.5 HU). A slightly higher attenuation difference was observed for iopromide 6 min after contrast medium injection (82.2 HU), although not statistically significant (p = 0.6437). Mean infarct volume as measured by NBT staining was 33.5% ± 13.6%. There was an excellent agreement of infarct sizes among NBT-, iopromide- and iodixanol-enhanced MDCT with concordance-correlation coefficients ranging from ρ_{(c)  =} 0.9928–0.9982. Iopromide and iodixanol both allow a reliable assessment of MI with delayed contrast-enhanced MDCT.     

Individually adapted examination protocols for reduction of radiation exposure for 16-MDCT chest examinations

OBJECTIVE: The purpose of our study was to develop a simple protocol for reduction of radiation exposure without loss of diagnostic information in chest 16-MDCT. MATERIALS AND METHODS: Two hundred and four patients underwent MDCT of the thorax (Somatom Sensation 16, Siemens). Group 1 was scanned using a standard protocol with 100 mAs(effective) (mAs(eff)). Group 2 was scanned using a dose modulation template (CareDose). Group 3 was scanned with mAs(eff) = body weight (kg). Group 4 was scanned with a combination of weight-adapted mAs(eff) and dose modulation. All other parameters were kept constant. Signal-to-noise ratio was assessed as an objective measurement for image quality, and subjective image quality was rated by three experienced radiologists on a 4-point scale. Effective dose was calculated using dedicated software. RESULTS: The mean noise measurement values were 8.31 H for the 100 mAs(eff) protocol for the regression between weight and signal-to-noise (p < 0.0001), 9.08 H for group 2 (p < 0.0001), 9.0 H for group 3 (p = 0.5051), and 9.98 H for group 4 (p = 0.0152). The median image quality was 1 (1 = highest quality) in all subgroups. The mean effective dose was 6.83 mSv, 5.92 mSv, 4.73 mSv, and 3.97 mSv, respectively. The least correlation between weight and image noise was achieved for the individually weight-adapted protocol and in the weight-adapted with CareDose combination. CONCLUSION: By tube current time product adaptation (kg = mAs(eff)) combined with an online tube current modulation template, a well-balanced examination without significant loss of information was achieved for this specific scanner. Thus, individually adapted protocols for chest 16-MDCT can be recommended.     

Dose reduction in computed tomography by attenuation-based on-line modulation of tube current: evaluation of six anatomical regions

This study investigated the potential of attenuation-based on-line modulation of tube current to reduce the dose of computed tomography (in milliamperes) without loss in image quality. The dose can be reduced for non-circular patient cross-sections by reducing the tube current at the angular positions at which the diameter through the patient diameter is smallest. We investigated a new technical approach with attenuation-based on-line modulation of tube current. Computed tomographic projection data were analyzed to determine the optimal milliampere values for each projection angle in real time, instead of performing prior measurements with localizer radiographs. We compared image quality, noise pattern, and dose for standard scans and for scans with attenuation-based on-line modulation of tube current in a group of 30 radiation therapy patients. Six different anatomical regions were examined: head, shoulder, thorax, abdomen, pelvis, and extremities (knee). Image quality was evaluated by four radiologists in a blinded fashion. We found the dose to be reduced typically by 15–50 %. In general, no deterioration in image quality was observed. Thus the dose in computed tomography be reduced substantially by technical measures without sacrificing image quality. Attenuation-based on-line modulation of tube current is an efficient and practical means for this. Received: 15 July 1999; Revised: 22 October 1999; Accepted: 26 October 1999     

Variability of bronchial measurements obtained by sequential CT using two computer-based methods

This study aimed to evaluate the variability of lumen (LA) and wall area (WA) measurements obtained on two successive MDCT acquisitions using energy-driven contour estimation (EDCE) and full width at half maximum (FWHM) approaches. Both methods were applied to a database of segmental and subsegmental bronchi with LA > 4 mm² containing 42 bronchial segments of 10 successive slices that best matched on each acquisition. For both methods, the 95% confidence interval between repeated MDCT was between –1.59 and 1.5 mm² for LA, and –3.31 and 2.96 mm² for WA. The values of the coefficient of measurement variation (CV₁₀, i.e., percentage ratio of the standard deviation obtained from the 10 successive slices to their mean value) were strongly correlated between repeated MDCT data acquisitions (r > 0.72; p < 0.0001). Compared with FWHM, LA values obtained using EDCE were higher for LA < 15 mm², whereas WA values were lower for bronchi with WA < 13 mm²; no systematic EDCE underestimation or overestimation was observed for thicker-walled bronchi. In conclusion, variability between CT examinations and assessment techniques may impair measurements. Therefore, new parameters such as CV₁₀ need to be investigated to study bronchial remodeling. Finally, EDCE and FWHM are not interchangeable in longitudinal studies.     

A new approach to the assessment of lumen visibility of coronary artery stent at various heart rates using 64-slice MDCT

Coronary artery stent lumen visibility was assessed as a function of cardiac movement and temporal resolution with an automated objective method using an anthropomorphic moving heart phantom. Nine different coronary stents filled with contrast fluid and surrounded by fat were scanned using 64-slice multi-detector computed tomography (MDCT) at 50–100 beats/min with the moving heart phantom. Image quality was assessed by measuring in-stent CT attenuation and by a dedicated tool in the longitudinal and axial plane. Images were scored by CT attenuation and lumen visibility and compared with theoretical scoring to analyse the effect of multi-segment reconstruction (MSR). An average increase in CT attenuation of 144 ± 59 HU and average diminished lumen visibility of 29 ± 12% was observed at higher heart rates in both planes. A negative correlation between image quality and heart rate was non-significant for the majority of measurements (P > 0.06). No improvement of image quality was observed in using MSR. In conclusion, in-stent CT attenuation increases and lumen visibility decreases at increasing heart rate. Results obtained with the automated tool show similar behaviour compared with attenuation measurements. Cardiac movement during data acquisition causes approximately twice as much blurring compared with the influence of temporal resolution on image quality. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Whole-body CT in polytrauma patients: effect of arm positioning on thoracic and abdominal image quality

The purpose of this study is to assess the influence of different arm positioning techniques on thoracic and abdominal image quality and radiation dose of whole-body trauma CT (wbCT). One hundred and fifty polytrauma patients (104 male, mean age 47 ± 19) underwent wbCT with arms elevated above the head (group A, n = 50), alongside the abdomen (group B, n = 50), and on a pillow ventrally to the chest with both arms flexed (group C, n = 50). Two blinded, independent observers measured image noise and rated image quality (scores 1–3) of the liver, aorta, spleen, spine, and lower lungs. Radiation dose parameters were noted, and the abdomens’ anterior–posterior diameter and scan lengths were measured. Interreader agreements for image noise (r = 0.86; p < 0.001) and subjective image quality (k = 0.71–0.84) were good. Noise was lower (p < 0.05), image quality of the liver, aorta, spleen, and spine was higher, and radiation dose lower in group A than in groups B and C (p < 0.001, each). Image quality of the spleen, liver, and aorta were higher in group C than in group B (p < 0.05, each). No significant differences in scan length (p = 0.61) were found among groups. Abdominal anterior–posterior diameter correlated significantly with noise (r = 0.82; p < 0.01) and dose (r = 0.47; p < 0.001). Estimated effective radiation doses were significantly (p < 0.001) higher in groups B (21.2 mSv) and C (21.9 mSv) as compared to A (16.1 mSv). In wbCT for polytrauma patients, positioning of the arms above the head results in better image quality and lower radiation dose. Placing the flexed arms on a large pillow ventrally to the chest significantly improves image quality as compared to positioning alongside the abdomen.     

Computed tomography during cardiopulmonary resuscitation using automated chest compression devices—an initial study

The purpose of the study was to evaluate both CT image quality in a phantom study and feasibility in an initial case series using automated chest compression (A-CC) devices for cardiopulmonary resuscitation (CPR). Multidetector CT (MDCT) of a chest/heart phantom (Thorax-CCI, QRM, Germany) was performed with identical protocols of the phantom alone (S), the phantom together with two different A-CC devices (A: AutoPulse, Zoll, Germany; L: LUCAS, Jolife, Sweden), and the phantom with a LUCAS baseplate, but without the compression unit (L-bp). Nine radiologists evaluated image noise quantitatively (n = 244 regions, Student’s t-test) and also rated image quality subjectively (1–excellent to 6–inadequate, Mann-Whitney U-test). Additionally, three patients during prolonged CPR underwent CT with A-CC devices. Mean image noise of S was increased by 1.21 using L-bp, by 3.62 using A, and by 5.94 using L (p < 0.01 each). Image quality was identical using S and L-bp (1.64 each), slightly worse with A (1.83), and significantly worse with L (2.97, p < 0.001). In all patient cases the main lesions were identified, which led to clinical key decisions. Image quality was excellent with L-bp and good with A. Under CPR conditions initial cases indicate that MDCT diagnostics supports either focused treatment or the decision to terminate efforts.     

Dose reduction in CT by on-line tube current control: principles and validation on phantoms and cadavers

We investigated approaches to reducing the dose in CT without impairing image quality. Dose can be reduced for non-circular object cross-sections without a significant increase in noise if X-ray tube current is reduced at angular tube positions where the X-ray attenuation by the patients is small. We investigated different schemes of current modulation during tube rotation by simulation and phantom measurements. Both pre-programmed sinusoidal modulation functions and attenuation-based on-line control of the tube current were evaluated. All relevant scan parameters were varied, including constraints such as the maximum modulation amplitude. A circular, an elliptical and two oval water phantoms were used. Results were validated on six cadavers. Dose reduction of 10–45 % was obtained both in simulations and in measurements for the different non-circular phantom geometries and current modulation algorithms without an increase in pixel noise values. On-line attenuation-based control yielded higher reductions than modulation by a sinusoidal curve. The maximal dose reduction predicted by simulations could not be achieved due to limits in the modulation amplitude. In cadaver studies, a reduction of typically 20–40 % was achieved for the body and about 10 % for the head. Variations of our technique are possible; a slight increase in nominal tube current for high-attenuation projections combined with attenuation-based current modulation still yields significant dose reduction, but also a reduction in the structured noise that may obscure diagnostic details. We conclude that a significant reduction in dose can be achieved by tube current modulation without compromising image quality. Attenuation-based on-line control and a modulation amplitude of at least 90 % should be employed. Received: 1 April 1998; Revision received: 9 July 1998; Accepted: 10 July 1998     

Multidetector CT urography: experimental analysis of radiation dose reduction in an animal model

The purpose of this study was to evaluate the possibility of reducing X-ray exposure during multidetector CT urography (MDCTU) considering image quality using a porcine model. MDCTU was performed in eight healthy pigs. Scanning was conducted using a gradual reduction of the tube current-time product at 120 kV [200–20 mAs (eff.) in ten steps]. Three blinded observers independently evaluated the image data for anatomic detail, subjective image quality, and subjective image noise. Overall image quality was compared to milliampere-second settings and radiation dose. Objective noise measurements were assessed. Noise measurements in patients were also performed to verify the comparabilty of the animal model. Adequate image quality allowing for detailed visualization of the upper urinary tract was obtained when the tube current-time product was decreased to 70 eff. mAs at 120 kV. Image noise did not impair image quality to a relevant degree using these parameters. There was high agreement among the observers (ICC = 0.95). In the animal experiments, reduced-dose MDCTU produced good image quality. A maximum current-time product reduction to 70 eff. mAs at 120 kV (CTDI_vol = 5.3 mGy) proved to be feasible, thereby offering an advantageous dosage reduction. The study provides a basis for the development of reduced-dose MDCTU protocols in humans.     

Can abdominal multi-detector CT diagnose spinal osteoporosis?

The aim of this study was to (1) generate quantitative CT (QCT) densitometric data based on routine abdominal multi-detector (MDCT) examinations and (2) investigate whether these data can be used to differentiate osteoporotic from healthy females. Twenty-five female patients (group A) with a history of radiotherapy were examined both with routine abdominal MDCT and standard QCT to generate a MDCT-to-QCT conversion equation. Twenty-one osteoporotic (group B) and 23 healthy female patients (group C) were also recruited in the study. Patients of groups B and C underwent routine abdominal MDCT examination for various clinical indications. Mean bone mineral density (BMD) in patients of group A was 103.4 mg/ml ± 32.8 with routine abdominal MDCT and 91.0 mg/ml ± 28.5 with QCT. Quantitative CT BMD_QCT values for patients in groups B and C were calculated utilizing the BMD_MDCT values derived from routine abdominal MDCT data sets and the MDCT to QCT conversion equation: . The calculated QCT densitometric data adequately differentiated osteoporotic from healthy females (area under ROC curve 0.828, p = 0.05). In conclusion, this study showed that in a group of female patients, QCT data derived from routine abdominal MDCT examinations discriminated osteoporotic from healthy subjects.     

Acute abdominal pain: value of non-contrast enhanced ultra-low-dose multi-detector row CT as a substitute for abdominal radiographs

The aim of this study was to evaluate a non-enhanced ultra-low-dose (ULD) abdominal–pelvic multi-detector row computerized tomography (MDCT) to assess patients with acute abdominal pain who would otherwise undergo three-view abdominal X-ray series. Institutional review board approval was obtained with waiver of informed consent. This study was Health Insurance Portability and Accountability Act-compliant. One hundred and sixty-three patients (mean age, 51 years; range, 19–82 years, M/F = 110:53) who underwent ULD MDCT were included in the study. Two subspecialty radiologists independently reviewed the images for abnormal findings and image quality parameters. The effective radiation dose was calculated for each patient and compared to standard-dose computed tomography (CT) scans of 50 matched controls. Findings were confirmed by reviewing the patients’ medical records, and statistical analysis was performed. ULD MDCT showed a high sensitivity (100%), specificity (98.5%), and positive predictive value (91.7%) for detection of free air, stones, and intestinal obstruction. For other sources of abdominal pain, the overall sensitivity, specificity, and positive predictive value were 86%, 96%, and 95%, respectively. Mean effective radiation dose from this study was 2.10 mSv (range of 0.67 to 6.64 mSv) with a 78% mean dose reduction compared to standard-dose CT. There was good inter-observer agreement (=0.4 to 0.81). ULD abdominal–pelvic MDCT provides rapid and reasonably accurate diagnostic information in patients with acute abdominal pain at a very low radiation dose. No financial grants were received for this study.     

Radioembolisation with <Superscript>90</Superscript>Y-microspheres: dosimetric and radiobiological investigation for multi-cycle treatment

Introduction  Radioembolisation with ⁹⁰Y-microspheres is a new locoregional treatment of hepatic lesions, usually applied as single cycle. Multi-cycle treatments might be considered as a strategy to improve the risk-benefit balance. With the aim to derive suitable information for patient tailored therapy, available patients’ dosimetric data were reviewed according to the linear–quadratic model and converted into biological effective dose (BED) values. Single vs. multi-cycle approaches were compared through radiobiological perspective. Materials and methods  Twenty patients with metastatic lesions underwent radioembolisation. The ⁹⁰Y-administered activity (AA) was established in order to respect a precautionary limit dose (40 Gy) for the non-tumoral liver (NTL). BED was calculated setting α/β = 2.5 Gy (NTL), 10 Gy (tumours); T _1/2,eff = T _1/2,phys = 64.2 h; T _1/2,rep = 2.5 h (NTL), 1.5 h (tumours). The BED to NTL was considered as a constraint for multi-cycle approach. The AA for two cycles and the percent variations of AA, tumour dose, BED were estimated. Results  In one-cycle, for a prescribed BED to NTL of 64 Gy (NTL dose = 40 Gy), AA was 1.7 (0.9–3.2) GBq, tumour dose was 130 (65–235) Gy, and tumour BED was 170 (75–360) Gy. Considering two cycles, ∼15% increase was found for AA and dose to NTL, with unvaried BED for NTL. Tumour dose increase was 20 (10–35) Gy; tumour BED increase was 10 (3–11) Gy. In different protocols allowing 80 Gy to NTL, the BED sparing estimated was ∼50 Gy (two cycles) and 65 Gy (three cycles). Conclusions  From a radiobiological perspective, multi-cycle treatments would allow administering higher activities with increased tumour irradiation and preserved radiation effects on NTL. Trials comparing single vs. multiple cycles are suggested.     

Semi-automated measurement of hyperdense,hypodense and heterogeneous hepatic metastasis on standard MDCT slices. Comparison of semi-automated and manual measurement of RECIST and WHO criteria

As semi-automated measurement would be desirable for lesion quantification and therapy-response control, the purpose of this study was to compare semi-automated measurements with manual assessment of different types of hepatic metastases. Seventy-six patients with known liver metastases were analysed. All of them underwent contrast-enhanced 16-MDCT (16 × 0.75 mm collimation, 120 kV, 0.5 s rotation time, 160 mAs_eff) for evaluation of follow-up status. On the basis of standard reconstructed 5-mm slices (in 4-mm increments), each lesion was quantified based on RECIST and WHO criteria using a semi-automated software tool (Syngo Oncology) and also manually by an experienced radiologist. Results from the software were compared to manual measurements. Statistical analysis was performed applying the concordance correlation coefficient, and results were represented graphically in Bland-Altman plots. A total of 52 hyperdense, 57 hypodense and 56 heterogeneous metastases were found and correctly measured by the software. All three lesion types revealed a strong correlation agreement between measurement techniques [RECIST diameter: 0.93 (hyperdense), 0.95(hypodense), 0.94 (heterogeneous); WHO area: 0.95, 0.98, 0.93]. Semi-automatic measurement of hyperdense, hypodense and heterogeneous liver metastases showed reliable results on standard axial reconstructions in comparison to manual quantification.     

Quantitative prediction of contrast enhancement from test bolus data in cardiac MSCT

The purpose of this study was to evaluate a new algorithm for the prediction of contrast enhancement from test bolus data in cardiac multislice spiral computed tomography (MSCT). An algorithm for the prediction of contrast enhancement using test bolus data was developed. A total of 30 consecutive patients (15 male, 69.5 ± 9.6 years) underwent cardiac MSCT (12 × 0.75 mm, 120 kV, 500 mAs_eff.) with a biphasic contrast material injection protocol. Contrast timing was derived from a standard 20 ml test bolus injection. Based on the test bolus time attenuation curves, expected enhancement values were computed for the ascending and descending aorta and the pulmonary trunk and compared with measured data from the cardiac CT scan. At the level of the test bolus measurement in the ascending aorta, the corresponding attenuation values were 309.4 ± 49.6 Hounsfield Units (HU) for the predicted and 285.6 ± 42.6 HU for the measured attenuation, respectively. The mean deviation between predicted and measured CT values was 32.8 ± 48.2 HU (upper and lower limits of agreement 101.4/−53.8 HU), indicating a slight systematic tendency for overestimation. For 80% of the patients the prediction error was less than 50 HU. Prediction of contrast enhancement in cardiac MSCT from test bolus data is feasible with a relatively small mean deviation; 80% of the predictions were within a range that might be acceptable for routine clinical application.     

Radiation dose estimates in dual-source computed tomography coronary angiography

The purpose of this study was to quantify radiation dose parameters of dual-source CT coronary angiography. Eighty patients underwent contrast-enhanced, retrospectively ECG-gated dual-source CT coronary angiography with heart rate-adapted ECG pulsing using two algorithms: In 40 patients, the tube current was reduced to 20% (A_min1) of the normal tube current (A_max) outside the pulsing window; in 40 patients tube current was reduced to 4% (A_min2) of A_max. Mean CTDI_vol in the A_min1 group was 45.1 ± 3.6 mGy; the mean CTDI_vol in the A_min2 group was 39.1 ± 3.2 mGy, with CTDI_vol in the A_min2 group being significantly reduced when compared to the A_min1 group (P < 0.001). A significant negative correlation was found between CTDI_vol and heart rate in group A_min1 (r = −0.82, P < 0.001), whereas no correlation was found between CTDI_vol and heart rate in group A_min2 (r = −0.066). Using the conversion coefficient for the chest, dual-source CT coronary angiography resulted in an estimated mean effective dose of 8.8 mSv in the A_min1 group and 7.8 mSv in the A_min2. Radiation exposure of dual-source CT coronary angiography using an ECG-pulsing protocol reducing the tube current to 20% significantly decreases with increasing heart rates, despite using wider pulsing windows at higher heart rates. When using a protocol with reduced tube current of 4%, the radiation dose is significantly lower, irrespective of the heart rate.     

Delineation of temporal bone anatomy: feasibility of low-dose 64-row CT in regard to image quality

The aim of our present study was to evaluate the visualization of anatomical landmarks of the temporal bone using a low-dose 64-slice computed tomography (CT) technique. A total of 120 patients were evaluated, 60 patients (mean age 47.1 years; 36 male, 24 female) underwent examination with a 4-slice CT scanner: 180 mAs, 120 kV, 1 s rotation time, 2 × 0.5 mm collimation, 0.5 mm slice thickness. Another 60 consecutive patients (mean age 37.4 years; 43 male, 37 female) were examined using a 64-slice CT low-dose protocol: 140 mAs, 120 kV, 1 s rotation time, 12 × 0.6 mm collimation, 0.6 mm slice thickness. The visibility of 42 landmarks was scored by two blinded radiologists using a five-point quality rating scale. Mean equivalent dose was significantly lower for the 64-slice CT protocol (0.31 mSv ± 0.12 mSv) compared to the 4-slice CT protocol (0.61 mSv ± 0.08 mSv). Despite increased image noise, only 19% of the anatomical landmarks were delineated significantly better on the axial sections of the 4-slice CT and only 9.5% of the anatomical landmarks on the reformatted coronal images. The interobserver agreement did not differ significantly between the two modalities. Low-dose 64-slice CT technique facilitates temporal bone imaging with sufficient anatomical detail.