Comparison of dual-source and electron-beam CT for the assessment of coronary artery calcium scoring

Objective

Cardiac CT allows the detection and quantification of coronary artery calcification (CAC). Electron-beam CT (EBCT) has been widely replaced by high-end CT generations in the assessment of CAC. The aim of this study was to compare the CAC scores derived from an EBCT with those from a dual-source CT (DSCT).

Methods

We retrospectively selected 92 patients (61 males; mean age, 60.7±12 years) from our database, who underwent both EBCT and DSCT. CAC was assessed using the Agatston score by two independent readers (replicates: 1, 2; 3=mean of reading 1 and 2).

Results

EBCT scores were on average slightly higher than DSCT scores (281±569 vs 241±502; p<0.05). In regression analysis R²-values vary from 0.956 (1) to 0.966 (3). We calculated a correction factor as EBCT=(DSCT+1)^1.026–1. When stratifying into CAC categories (0, 1–99, 100–399, 400–999 and ≥1000), 79 (86%) were correctly classified. From those with positive CAC scores, 7 out of 61 cases (11%, κ=0.81) were classified in different categories. Using the corrected DSCT CAC score, linear regression analysis for the comparison to the EBCT results were r=0.971 (p<0.001), with a mean difference of 6.4±147.8. Five subjects (5.4%) were still classified in different categories (κ=0.84).

Conclusion

CAC obtained from DSCT is highly correlated with the EBCT measures. Using the calculated correction factor, agreement only marginally improved the clinical interpretation of results. Overall, for clinical purposes, face value use of DSCT-derived values appears as useful as EBCT for CAC scoring.Cardiac CT allows the detection and quantification of coronary artery calcification (CAC) and may thus add important in vivo information on the path from risk factor exposure to formation of clinical events [1-4]. Because of its advantages of being a fast technique with limited radiation exposure to the patients, various published clinical outcome data from CAC are based on electron-beam CT (EBCT), and therefore cut-points have been established for EBCT scans. However, since the appearance of newer generations of CT scanners such as dual-source CT (DSCT), scanners of this type are also widely used for CAC scoring as an alternative to EBCT. The spatial resolution of DSCT scanners is much higher, enabling the detection of smaller lesions, and DSCT is more applicable to other radiological procedures such as CT angiography [5]. CAC scoring is performed on these newer scanner generations using the Agatston score algorithm as the standard measure of CAC quantification. There is direct comparison of CAC scores between newer scanners and EBCT [6-9]. However, comparison between EBCT and DSCT is rare [10]. This is of interest for first-time CAC scoring in asymptomatic subjects, and especially for evaluation of disease progression in subjects with prior EBCT testing. Therefore, the aim of this study was to evaluate the diagnostic accuracy of DSCT in the detection of CAC scores to EBCT. In addition, we compared techniques with each other, verifying the ability of CAC score classification.     

Effect of Heart Rate and Coronary Calcification on the Diagnostic Accuracy of the Dual-Source CT Coronary Angiography in Patients with Suspected Coronary Artery Disease

Objective

To evaluate the diagnostic accuracy of a dual-source computed tomography (DSCT) coronary angiography, with a particular focus on the effect of heart rate and calcifications.

Materials and Methods

One hundred and nine patients with suspected coronary disease were divided into 2 groups according to a mean heart rate (< 70 bpm and ≥ 70 bpm) and into 3 groups according to the mean Agatston calcium scores (≤ 100, 101-400, and > 400). Next, the effect of heart rate and calcification on the accuracy of coronary artery stenosis detection was analyzed by using an invasive coronary angiography as a reference standard. Coronary segments of less than 1.5 mm in diameter in an American Heart Association (AHA) 15-segment model were independently assessed.

Results

The mean heart rate during the scan was 71.8 bpm, whereas the mean Agatston score was 226.5. Of the 1,588 segments examined, 1,533 (97%) were assessable. A total of 17 patients had calcium scores above 400 Agatston U, whereas 50 had heart rates ≥ 70 bpm. Overall the sensitivity, specificity, positive predictive values (PPV) and negative predictive values (NPV) for significant stenoses were: 95%, 91%, 65%, and 99% (by segment), respectively and 97%, 90%, 81%, and 91% (by artery), respectively (n = 475). Heart rate showed no significant impact on lesion detection; however, vessel calcification did show a significant impact on accuracy of assessment for coronary segments. The specificity, PPV and accuracy were 96%, 80%, and 96% (by segment), respectively for an Agatston score less than 100% and 99%, 96% and 98% (by artery). For an Agatston score of greater to or equal to 400 the specificity, PPV and accuracy were reduced to 79%, 55%, and 83% (by segment), respectively and to 79%, 69%, and 85% (by artery), respectively.

Conclusion

The DSCT provides a high rate of accuracy for the detection of significant coronary artery disease, even in patients with high heart rates and evidence of coronary calcification. However, patients with severe coronary calcification (> 400 U) remain a challenge to diagnose.     

Potential clinical impact of variability in the measurement of coronary artery calcification with sequential MDCT

OBJECTIVE: The potential clinical impact of variability in the measurement of coronary artery calcification with sequential MDCT was evaluated using Agatston, volume, and mass scoring algorithms. SUBJECTS AND METHODS: Fifty-six patients were imaged twice using an identical prospectively ECG-triggered sequential scanning protocol. The Agatston, volume, and mass scores were computed by two observers independently. In addition, a patient's total Agatston score was referenced to an age- and sex-stratified database to determine a percentile ranking. Interscan, interobserver, and intraobserver variability and the resultant impact on patients' risk stratifications were assessed. RESULTS: Significant interscan differences were found for all mean coronary calcium scores (Wilcoxson's signed rank test, p <0.0001). Although the median percentage of interscan variability was low for all scoring methods, the interquartile range was wide, indicating significant variability in the data. Median scores (lower quartile-upper quartile) for observers 1 and 2, respectively, were as follows: Agatston, 5% (0-79%) and 6% (0-83%); volume, 12% (0-51%) and 12% (0-57%); and mass, 14% (0-57%) and 14% (0-58%). Interobserver and intraobserver differences between mean calcium scores were not significant, and consequently, lower interobserver and intraobserver variabilities (narrow interquartile ranges of 0-5%) were observed for all scores. Despite significant interscan differences in calcium scores, the percentile ranking assigned to the two scans differed in only 13% of patients. Interobserver differences resulted in a change in the percentile ranking in 7-9% of patients, whereas intraobserver differences caused a change in only 5% of patients. CONCLUSION: The accuracy of sequential MDCT for coronary calcium quantification is sufficient in most cases for stratification of patient risk.     

High-Definition Computed Tomography for Coronary Artery Stent Imaging: a Phantom Study

Objective

To assess the performance of a high-definition CT (HDCT) for imaging small caliber coronary stents (≤ 3 mm) by comparing different scan modes of a conventional 64-row standard-definition CT (SDCT).

Materials and Methods

A cardiac phantom with twelve stents (2.5 mm and 3.0 mm in diameter) was scanned by HDCT and SDCT. The scan modes were retrospective electrocardiography (ECG)-gated helical and prospective ECG-triggered axial with tube voltages of 120 kVp and 100 kVp, respectively. The inner stent diameters (ISD) and the in-stent attenuation value (AV_in-stent) and the in-vessel extra-stent attenuation value (AV_in-vessel) were measured by two observers. The artificial lumen narrowing (ALN = [ISD - ISD_measured]/ISD) and artificial attenuation increase between in-stent and in-vessel (AAI = AV_in-stent - AV_in-vessel) were calculated. All data was analyzed by intraclass correlation and ANOVA-test.

Results

The correlation coefficient of ISD, AV_in-vessel and AV_in-stent between the two observers was good. The ALNs of HDCT were statistically lower than that of SDCT (30 ± 5.7% versus 35 ± 5.4%, p < 0.05). HDCT had statistically lower AAI values than SDCT (15.7 ± 81.4 HU versus 71.4 ± 90.5 HU, p < 0.05). The prospective axial dataset demonstrated smaller ALN than the retrospective helical dataset on both HDCT and SDCT (p < 0.05). Additionally, there were no differences in ALN between the 120 kVp and 100 kVp tube voltages on HDCT (p = 0.05).

Conclusion

High-definition CT helps improve measurement accuracy for imaging coronary stents compared to SDCT. HDCT with 100 kVp and the prospective ECG-triggered axial technique, with a lower radiation dose than 120 kVp application, may be advantageous in evaluating coronary stents with smaller calibers (≤ 3 mm).     

Evidence for lower variability of coronary artery calcium mineral mass measurements by multi-detector computed tomography in a community-based cohort--consequences for progression studies

PURPOSE: To compare the measurement variability for coronary artery calcium (CAC) measurements using mineral mass compared with a modified Agatston score (AS) or volume score (VS) with multi-detector CT (MDCT) scanning, and to estimate the potential impact of these methods on the design of CAC progression studies. MATERIALS AND METHODS: We studied 162 consecutive subjects (83 women, 79 men, mean age 51 +/- 11 years) from a general Caucasian community-based cohort (Framingham Heart Study) with duplicate runs of prospective electrocardiographically-triggered MDCT scanning. Each scan was independently evaluated for the presence of CAC by four experienced observers who determined a "modified" AS, VS and mineral mass. RESULTS: Of the 162 subjects, CAC was detected in both scans in 69 (42%) and no CAC was detected in either scan in 72 (45%). Calcium scores were low in the 21/162 subjects (12%) for whom CAC was present in one but not the other scan (modified AS < 20 in 20/21 subjects, mean AS 4.6 +/- 1.9). For all three quantification algorithms, the inter- and intraobserver correlation were excellent (r > 0.96). However, the mean interscan variability was significantly different between mineral mass, modified AS, and VS (coefficient of variation 26 +/- 19%, 41 +/- 28% and 34 +/- 25%, respectively; p < 0.04), with significantly smaller mean differences in pair-wise comparisons for mineral mass compared with modified AS (p < 0.002) or with VS (p < 0.03). The amount of CAC but not heart rate was an independent predictor of interscan variability (r = -0.638, -0.614 and -0.577 for AS, VS, and mineral mass, respectively; all p < 0.0001). The decreased interscan variability of mineral mass would allow a sample size reduction of 5.5% compared with modified AS for observational studies of CAC progression and for randomized clinical trials. CONCLUSION: There is significantly reduced interscan variability of CAC measurements with mineral mass compared with the modified AS or VS. However, the measurement variability of all quantification methods is predicted by the amount of CAC and is inversely correlated to the extent of partial volume artifacts. Moreover, the improvement of measurement reproducibility leads to a modest reduction in sample size for observational epidemiological studies or randomized clinical trials to assess the progression of CAC.     

Improved reproducibility of coronary artery calcium scoring by electron beam tomography with a new electrocardiographic trigger method

RATIONALE AND OBJECTIVES: To improve the interscan reproducibility with electron beam tomography (EBT) by choosing an optimal electrocardiographic (ECG) trigger time. METHODS: Two hundred fourteen asymptomatic subjects found to have coronary artery calcium (CAC) on EBT were rescanned immediately to measure the interscan variability. Subjects were randomized to one of two different ECG trigger interval groups: the new trigger method (group 1) and the 80% R-R interval trigger method (group 2). The new trigger method was derived from a previous study of motion in the coronary arteries. In group 1 (new trigger method), the ECG trigger was programmed for a certain time (in ms) after the R wave, based on the resting heart rate. The triggers for group 1 were 360 (heart rate <50 beats per minute [bpm]), 340 (51--60 bpm), 314 (61--70 bpm), 300 (71--80 bpm), 290 (81--90 bpm), 280 (91--100 bpm), and 270 ms (>100 bpm). The interscan variation (CAC area and Agatston score) was compared between the two groups. RESULTS: The interscan variability was significantly reduced using the new trigger method for both CAC area and score compared with the 80% trigger method. The individual lesion variation was also significantly reduced by the new trigger method compared with the 80% trigger method. Area measure had a significantly lower variability compared with the Agatston score. CONCLUSIONS: These results strongly support the use of this new ECG trigger that relies on a rate-adjusted millisecond delay after the R wave instead of the more commonly used 80% R-R interval in EBT calcium studies.     

The modulation transfer function and signal-to-noise ratio of different digital filters: a technical approach

Objectives

The aim of this study was to illustrate the influence of digital filters on the signal-to-noise ratio (SNR) and modulation transfer function (MTF) of digital images. The article will address image pre-processing that may be beneficial for the production of clinically useful digital radiographs with lower radiation dose.

Methods

Three filters, an arithmetic mean filter, a median filter and a Gaussian filter (standard deviation (SD) = 0.4), with kernel sizes of 3 × 3 pixels and 5 × 5 pixels were tested. Synthetic images with exactly increasing amounts of Gaussian noise were created to gather linear regression of SNR before and after application of digital filters. Artificial stripe patterns with defined amounts of line pairs per millimetre were used to calculate MTF before and after the application of the digital filters.

Results

The Gaussian filter with a 5 × 5 kernel size caused the highest noise suppression (SNR increased from 2.22, measured in the synthetic image, to 11.31 in the filtered image). The smallest noise reduction was found with the 3 × 3 median filter. The application of the median filters resulted in no changes in MTF at the different resolutions but did result in the deletion of smaller structures. The 5 × 5 Gaussian filter and the 5 × 5 arithmetic mean filter showed the strongest changes of MTF.

Conclusions

The application of digital filters can improve the SNR of a digital sensor; however, MTF can be adversely affected. As such, imaging systems should not be judged solely on their quoted spatial resolutions because pre-processing may influence image quality.     

Diagnostic Value of 64-Slice Dual-Source CT Coronary Angiography in Patients with Atrial Fibrillation: Comparison with Invasive Coronary Angiography

Objective

We wanted to evaluate the image quality and diagnostic value of 64-slice dual-source computed tomography (DSCT) coronary angiography in patients with atrial fibrillation (Afib).

Materials and Methods

The coronary arteries of 22 Afib patients seen on DSCT were classified into 15 segments and the imaging quality (excellent, good, moderate and poor) and significant stenoses (≥ 50%) were evaluated by two radiologists who were blinded to the conventional coronary angiography (CAG) results. The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for detecting important coronary artery stenosis were calculated. McNemar test was used to determine any significant difference between DSCT and CAG, and Cohen''s Kappa statistics were calculated for the intermodality and interobserver agreement.

Results

The mean heart rate was 89 ± 8.3 bpm (range: 80-118 bpm). A range from 250 msec to 300 msec within the RR interval was the optimal reconstruction interval for the patients with Afib. The respective overall sensitivity, specificity, PPV and NPV values were 74%, 97%, 81% and 96% for reader 1 and 72%, 98%, 85% and 96% for reader 2. No significant difference between DSCT and CAG was found for detecting a significant stenosis (reader 1, p = 1.0; reader 2, p = 0.727). Cohen''s Kappa statistics demonstrated good intermodality and interobserver agreement.

Conclusion

64-slice DSCT coronary angiography provides good image quality in patients with atrial fibrillation without the need for controlling the heart rate. DSCT can be used for ruling out significant stenosis in patients with atrial fibrillation with its high NPV for detecting in important stenosis.     

Prospectively Electrocardiogram-Gated High-Pitch Spiral Acquisition Mode Dual-Source CT Coronary Angiography in Patients with High Heart Rates: Comparison with Retrospective Electrocardiogram-Gated Spiral Acquisition Mode

Objective

To assess the image quality and effective radiation dose of prospectively electrocardiogram (ECG)-gated high-pitch spiral acquisition mode (flash mode) of dual-source CT (DSCT) coronary angiography (CTCA) in patients with high heart rates (HRs) as compared with retrospectively ECG-gated spiral acquisition mode.

Materials and Methods

Two hundred and sixty-eight consecutive patients (132 female, mean age: 55 ± 11 years) with mean HR > 65 beats per minute (bpm) were prospectively included in this study. The patients were divided into two groups. Collection was performed in group A CTCA using flash mode setting at 20-30% of the R-R interval, and retrospectively ECG-gated spiral acquisition mode in group B. The image noise, contrast-to-noise ratio (CNR), image quality scores, effective radiation dose and influencing factors on image quality between the two groups were assessed.

Results

There were no significant differences in image quality scores and proportions of non-diagnostic coronary artery segments between two groups (image quality scores: 1.064 ± 0.306 [group A] vs. 1.084 ± 0.327 [group B], p = 0.063; proportion of non-diagnostic coronary artery segments: segment-based analysis 1.52% (group A) vs. 1.74% (group B), p = 0.345; patient-based analysis 7.5% (group A) vs. 6.7% (group B), p = 0.812). The estimated radiation dose was 1.0 ± 0.16 mSv in group A and 7.1 ± 1.05 mSv in group B (p = 0.001).

Conclusion

In conclusion, in patients with HRs > 65 bpm without cardiac arrhythmia, the prospectively high-pitch spiral-acquisition mode with image-acquired timing set at 20-30% of the R-R interval provides a similar image quality and low rate of non-diagnostic coronary segments to the retrospectively ECG-gated low-pitch spiral acquisition mode, with significant reduction of radiation exposure.     

Calcium scoring with prospectively ECG-triggered CT: Using overlapping datasets generated with MPR decreases inter-scan variability

Objective

To examine the feasibility of reducing the inter-scan variability of prospectively ECG-triggered calcium-scoring scans by using overlapping 3-mm datasets generated from multiplanar reformation (MPR) instead of non-overlapping 3-mm or 1.5-mm datasets.

Patients and methods

Seventy-five women (59–79 years old) underwent two sequential prospectively ECG-triggered calcium-scoring scans with 16 mm × 1.5 mm collimation in one session. Between the two scans patients got off and on the table. We performed calcium scoring (Agatston and mass scores) on the following datasets: contiguous 3-mm sections reconstructed from the raw data (A), contiguous 3-mm sections from MPR (B), overlapping 3-mm sections from MPR (C) and contiguous 1.5-mm sections from the raw data (D). To determine the feasibility of the MPR approach, we compared MPR (B) with direct raw data reconstruction (A). Inter-scan variability was calculated for each type of dataset (A–D).

Results

Calcium scores ranged from 0 to 1455 (Agatston) and 0 to 279 mg (mass) for overlapping 3-mm sections (C). Calcium scores (both Agatston and mass) were nearly identical for MPR (B) and raw data approaches (A), with inter-quartile ranges of 0–1% for inter-scan variability. Median inter-scan variability with contiguous 3-mm sections (B) was 13% (Agatston) and 11% (mass). Median variability was reduced to 10% (Agatston and mass) with contiguous 1.5-mm sections (D) and to 8% (Agatston) and 7% (mass) with overlapping 3-mm MPR (A).

Conclusion

Calcium scoring on MPR yields nearly identical results to calcium scoring on images directly reconstructed from raw data. Overlapping MPR from prospectively ECG-triggered scans improve inter-scan variability of calcium scoring without increasing patient radiation dose.     

Computer-Aided Classification of Visual Ventilation Patterns in Patients with Chronic Obstructive Pulmonary Disease at Two-Phase Xenon-Enhanced CT

Objective

To evaluate the technical feasibility, performance, and interobserver agreement of a computer-aided classification (CAC) system for regional ventilation at two-phase xenon-enhanced CT in patients with chronic obstructive pulmonary disease (COPD).

Materials and Methods

Thirty-eight patients with COPD underwent two-phase xenon ventilation CT with resulting wash-in (WI) and wash-out (WO) xenon images. The regional ventilation in structural abnormalities was visually categorized into four patterns by consensus of two experienced radiologists who compared the xenon attenuation of structural abnormalities with that of adjacent normal parenchyma in the WI and WO images, and it served as the reference. Two series of image datasets of structural abnormalities were randomly extracted for optimization and validation. The proportion of agreement on a per-lesion basis and receiver operating characteristics on a per-pixel basis between CAC and reference were analyzed for optimization. Thereafter, six readers independently categorized the regional ventilation in structural abnormalities in the validation set without and with a CAC map. Interobserver agreement was also compared between assessments without and with CAC maps using multirater κ statistics.

Results

Computer-aided classification maps were successfully generated in 31 patients (81.5%). The proportion of agreement and the average area under the curve of optimized CAC maps were 94% (75/80) and 0.994, respectively. Multirater κ value was improved from moderate (κ = 0.59; 95% confidence interval [CI], 0.56-0.62) at the initial assessment to excellent (κ = 0.82; 95% CI, 0.79-0.85) with the CAC map.

Conclusion

Our proposed CAC system demonstrated the potential for regional ventilation pattern analysis and enhanced interobserver agreement on visual classification of regional ventilation.     

Evaluation of CT coronary artery angiography with 320-row detector CT in a high-risk population

Objectives

The aim of this article was to prospectively evaluate the accuracy and radiation dose of 320-detector row dynamic volume CT (DVCT) for the detection of coronary artery disease (CAD) in a high-risk population.

Methods

60 patients with a high risk of CAD underwent DVCT without preceding heart rate control and also underwent invasive coronary angiography (ICA), which served as the standard reference.

Results

On a per segment analysis, overall sensitivity was 95.3%, specificity was 97.6%, positive predictive value was 90.6%, negative predictive value was 98.8% and Youden index was 0.93. In both heart rate subgroups, diagnostic accuracy for the assessment of coronary artery stenosis was similar. The accuracy of the subgroup with an Agatston score ≥100 was lower than that for patients with an Agatston score <100. However, the difference between DVCT and ICA results was not significant (p=0.08). The mean estimated effective dose of CT was 12.5±9.4 mSv. In those patients with heart rates less than 70 beats per minute (bpm), the mean radiation exposure of DVCT was 5.2±0.9 mSv. The effective radiation dose was significantly lower than that of ICA (14.1±5.9 mSv) (p<0.001). When the heart rate was >70 bpm, a significantly higher dose was delivered to patients with DVCT (22.6±5.2 mSv, p<0.001) than with ICA (15.0±5.3 mSv, p<0.001).

Conclusion

DVCT reliably provides high diagnostic accuracy without heart rate/rhythm control. However, from a dosimetric point of view, it is recommended that heart rate should be controlled to <70 bpm to decrease radiation dose.The small diameter of the coronary segments, their complex three-dimensional geometry and their rapid movement throughout the cardiac cycle represent the major challenges for artefact-free coronary CT angiography (CTA). With each scanner generation, motion artefacts re-appear as a major cause of image quality degradation during coronary CTA [1-10]. Coronary CTA studies of each coronary artery with four-multidetector CT (MDCT) at a gantry rotation time of 500 ms had significantly decreased image quality with increasing mean heart rates [3]. Using 16-MDCT at a gantry rotation time of 420 ms, Hoffmann et al [2] found a significant negative correlation between overall image quality and mean heart rate. Even using 64-section CT, with its gantry rotation speed of 330 ms, elevated and irregular heart beats were found to cause relevant degradation of image quality [1,4,9,11]. Using dual-source CT (DSCT) with an increased temporal resolution of 83 ms, there was no significant correlation between mean heart rate and the overall image quality for any coronary segment or for any individual coronary artery. Nonetheless, irregular heart rates still slightly affect the image quality of non-invasive coronary angiography, even with DSCT [10,12].The 320-detector row dynamic volume CT (DVCT) is characterised by 320 slice detectors with a thickness of 0.5 mm and gantry rotation time of 350 ms. With a wide coverage of 16 cm in the z-axis, the whole heart can be covered within one cardiac cycle. Theoretically, DVCT makes it possible to scan patients with an irregular heart rate without “stair-step” artefacts. At the same time, DVCT avoids the overlapping rotations of helical CT, and the application of prospective echocardiogram (ECG) gating has become more feasible. Recent studies of DVCT have mainly been based on a low heart rate [13-17]. Few studies have investigated the diagnostic accuracy in higher heart rates and arrhythmia. Our purpose was to systematically evaluate the diagnostic accuracy and exposure dose of DVCT in a high-risk population with high and irregular heart rates.     

The Adverse Events and Hemodynamic Effects of Adenosine-Based Cardiac MRI

Objective

We wanted to prospectively assess the adverse events and hemodynamic effects associated with an intravenous adenosine infusion in patients with suspected or known coronary artery disease and who were undergoing cardiac MRI.

Materials and Methods

One hundred and sixty-eight patients (64 ± 9 years) received adenosine (140 µg/kg/min) during cardiac MRI. Before and during the administration, the heart rate, systemic blood pressure, and oxygen saturation were monitored using a MRI-compatible system. We documented any signs and symptoms of potential adverse events.

Results

In total, 47 out of 168 patients (28%) experienced adverse effects, which were mostly mild or moderate. In 13 patients (8%), the adenosine infusion was discontinued due to intolerable dyspnea or chest pain. No high grade atrioventricular block, bronchospasm or other life-threatening adverse events occurred. The hemodynamic measurements showed a significant increase in the heart rate during adenosine infusion (69.3 ± 11.7 versus 82.4 ± 13.0 beats/min, respectively; p < 0.001). A significant but clinically irrelevant increase in oxygen saturation occurred during adenosine infusion (96 ± 1.9% versus 97 ± 1.3%, respectively; p < 0.001). The blood pressure did not significantly change during adenosine infusion (systolic: 142.8 ± 24.0 versus 140.9 ± 25.7 mmHg; diastolic: 80.2 ± 12.5 mmHg versus 78.9 ± 15.6, respectively).

Conclusion

This study confirms the safety of adenosine infusion during cardiac MRI. A considerable proportion of all patients will experience minor adverse effects and some patients will not tolerate adenosine infusion. However, all adverse events can be successfully managed by a radiologist. The increased heart rate during adenosine infusion highlights the need to individually adjust the settings according to the patient, e.g., the number of slices of myocardial perfusion imaging.     

Variability of repeated coronary artery calcium scoring and radiation Dose on 64- and 16-slice computed tomography by prospective electrocardiographically-triggered axial and retrospective electrocardiographically-gated spiral computed tomography: a phantom study

RATIONALE AND OBJECTIVES: We sought to compare coronary artery calcium (CAC) scores, the variability and radiation doses on 64- and 16-slice computed tomography (CT) scanners by both prospective electrocardiographically (ECG)-triggered and retrospective ECG-gated scans. MATERIALS AND METHODS: Coronary artery models (n = 3) with different plaque CT densities (approximately 240 Hounsfield units [HU], approximately 600 HU, and approximately 1000 HU) of four sizes (1, 3, 5, and 10 mm in length) on a cardiac phantom were scanned three times in five heart rate sequences. The tube current-time products were set to almost the same on all four protocols (32.7 mAs for 64-slice prospective and retrospective scans, 33.3 mAs for 16-slice prospective and retrospective scans). Slice thickness was set to 2.5 mm to keep the radiation dose low. Overlapping reconstruction with a 1.25-mm increment was applied on the retrospective ECG-gated scan. RESULTS: The CAC scores were not different between the four protocols (one-factor analysis of variance: Agatston, P = .32; volume, P = .19; and mass, P = .09). Two-factor factorial analysis of variance test revealed that the interscan variability was different between protocols (P < .01) and scoring algorithms (P < .01). The average variability of Agatston/volume/mass scoring and effective doses were as follows: 64-slice prospective scan: 16%/15%/11% and 0.5 mSv; 64-slice retrospective scan: 11%/11%/8% and 3.7 mSv; 16-slice prospective scan: 20%/18%/13% and 0.6 mSv; and 16-slice retrospective scan: 16%/15%/11% and 2.9 to 3.5 mSv (depending on the pitch). CONCLUSION: Retrospective ECG-gated 64-slice CT showed the lowest variability. Prospective ECG-triggered 64-slice CT, with low radiation dose, shows low variability on CAC scoring comparable to retrospective ECG-gated 16-slice CT.     

Radiologists' Performance for Detecting Lesions and the Interobserver Variability of Automated Whole Breast Ultrasound

Objective

To compare the detection performance of the automated whole breast ultrasound (AWUS) with that of the hand-held breast ultrasound (HHUS) and to evaluate the interobserver variability in the interpretation of the AWUS.

Materials and Methods

AWUS was performed in 38 breast cancer patients. A total of 66 lesions were included: 38 breast cancers, 12 additional malignancies and 16 benign lesions. Three breast radiologists independently reviewed the AWUS data and analyzed the breast lesions according to the BI-RADS classification.

Results

The detection rate of malignancies was 98.0% for HHUS and 90.0%, 88.0% and 96.0% for the three readers of the AWUS. The sensitivity and the specificity were 98.0% and 62.5% in HHUS, 90.0% and 87.5% for reader 1, 88.0% and 81.3% for reader 2, and 96.0% and 93.8% for reader 3, in AWUS. There was no significant difference in the radiologists'' detection performance, sensitivity and specificity (p > 0.05) between the two modalities. The interobserver agreement was fair to good for the ultrasonographic features, categorization, size, and the location of breast masses.

Conclusion

AWUS is thought to be useful for detecting breast lesions. In comparison with HHUS, AWUS shows no significant difference in the detection rate, sensitivity and the specificity, with high degrees of interobserver agreement.     

Coronary calcium screening in asymptomatic patients as a guide to risk factor modification and stress myocardial perfusion imaging

BACKGROUND: Previous studies have demonstrated a correlation between the extent of coronary artery calcification (CAC) and atherosclerotic plaque. As a result, CAC screening could be useful in predicting cardiovascular risk in individuals in whom atherosclerosis is developing. One possible method of detecting and quantifying CAC is by x-ray computed tomography, which potentially allows one to stratify patients into groups requiring risk factor modification or follow-up testing such as myocardial perfusion single photon emission computed tomography (SPECT). METHODS AND RESULTS: This study was designed to evaluate the clinical utility of multidetector computed tomography (MDCT) in a cardiology practice setting. A retrospective analysis was performed on data from 794 asymptomatic patients who underwent CAC screening over an 8-month period. On the basis of the CAC score and physician consultation, 102 patients underwent subsequent myocardial perfusion SPECT imaging. A substudy was also conducted in 306 patients to measure the interscan variability of MDCT across different CAC score ranges. CAC was detected in 422 of 794 patients. Of these, the CAC was moderate (Agatston score = 101-400) in 14% and severe (>400) in 9%. Patients with 3 or more cardiac risk factors were most likely to exhibit moderate to severe CAC. In myocardial perfusion SPECT testing, no patient with an Agatston score lower than 100 had an abnormal study. In contrast, 41% of patients with severe CAC had an abnormal SPECT study. In the reproducibility substudy the minimal CAC group had the largest variability (86.0%) whereas the severe CAC group had the lowest variability (9.5%). CONCLUSION: CAC screening with MDCT is justified for asymptomatic patients with 3 or more cardiac risk factors. However, risk factor assessment is poor at predicting which individuals will have CAC if fewer risk factors are present. In terms of the interscan variability, MDCT is capable of following changes in CAC for patients with Agatston scores greater than 100. Finally, this study demonstrated that an Agatston score of 400 is a logical threshold to initiate follow-up myocardial perfusion SPECT testing.     

Prostate cancer: contouring target and organs at risk by kilovoltage and megavoltage CT and MRI in patients with and without hip prostheses

Objective:

In radiotherapy treatment, planning target volume and organs at risk are contoured on kilovoltage CT (kVCT) images. Unlike MR images, kVCT does not provide precise information on target volume extension. Since neither kVCT nor MRI may be suitable for contouring in patients with ferrous hip prostheses, this study evaluated whether megavoltage CT (MVCT) reduced interobserver variability.

Methods:

Two patients without hip prostheses and one patient (Patient 3) with hip prostheses were enrolled. Six radiation oncologists contoured prostate, rectum and bladder on kVCT (Patients 1 and 3), MRI (Patient 2) and MVCT images (Patient 3). MVCT was acquired with fine, normal and coarse modalities. Interobserver variability for each organ was analysed using conformity index (CI) and coefficient of variation (CV).

Results:

In patients without hip prostheses, CIs were higher in prostate contouring with MRI than with kVCT, indicating lower interobserver variability with MRI. Very slight variations were seen in rectum and bladder contouring. In the patient with hip prostheses (Patient 3), contouring on kVCT lowered CI and increased CV in the prostate, bladder and rectum. The differences were more marked in the prostate. Only fine modality MVCT reduced interobserver variability and only for the prostate.

Conclusion:

Even though greater noise and less soft-tissue contrast increase contouring variability with MVCT than with kVCT, lack of artefacts on MVCT could provide better image definition by this modality in hip prosthesis patients in whom MRI is precluded.

Advances in knowledge:

We recommend the fine modality MVCT for contouring hip prostheses patients.     

Ex vivo comparison of Galileos cone beam CT and intraoral radiographs in detecting occlusal caries

Objective

The aim of this study was to compare the accuracy of cone beam CT (CBCT) with intraoral radiographs for detection of occlusal caries.

Methods

A set of 60 extracted teeth were imaged using a Sirona Galileos CBCT system (Sirona Dental Systems, Bensheim, Germany) and an intraoral Planmeca® system (Planmeca OY, Helsinki, Finland). Six observers looked at both modalities and used a five-point confidence scale to evaluate presence or absence of occlusal caries. Histology was used as the gold standard. Receiver operating characteristic analysis and weighted kappa statistics were used for statistical analysis. Differences in the area under the curve (AUC) values between observers and modalities were analysed using analysis of variance (ANOVA). Differences in sensitivity and specificity were analysed using the Wilcoxon test. Interobserver and intraobserver reliability was assessed by weighted kappa scores.

Results

The mean value and standard deviation of AUC was 0.719 ± 0.038 for CBCT and 0.649 ± 0.062 for the intraoral radiographs. The ANOVA results demonstrated that there was no significant difference between the modalities and the observers. The interobserver kappa for pairs of observers ranged from fair to substantial for bitewings (0.244–0.543) and CBCT (0.152–0.401). Four out of six observers reported higher sensitivity but lower specificity with CBCT. The Wilcoxon exact p-value showed no difference in sensitivity (0.175) or specificity (0.573) between the two modalities.

Conclusion

Based on the results we conclude that the Sirona CBCT unit cannot be used for the sole purpose of looking at occlusal caries.     

Effects of Propranolol on the Left Ventricular Volume of Normal Subjects During CT Coronary Angiography

Objective

The purpose of this study is to determine the effects of propranolol on the left ventricular (LV) volume during CT coronary angiography.

Materials and Methods

The LV volume of 252 normal Chinese subjects (126 subjects with propranolol medication and 126 age- and gender-matched Chinese subjects without medication) was estimated using 64 slices multi-detector CT (MDCT). The heart rate difference was analyzed by the logistic linear regression model with variables that included gender, age, body height, body weight, systolic blood pressure (SBP), diastolic blood pressure (DBP) and the dosage of propranolol. The following global LV functional parameters were calculated: the real-end diastolic volume (EDV), the real-end systolic volume (ESV) and the real-ejection fraction (EF).

Results

The female subjects had a greater decrease of heart rate after taking propranolol. The difference of heart rate was negatively correlated with the dosage of propranolol. The real-EDV, the real-ESV and the real-EF ranged from 48.1 to 109 mL/m², 6.1 to 57.1 mL/m² and 41% to 88%, respectively. There was no significant difference in the SBP and DBP between the groups without and with propranolol medication (123 ± 17 and 80 ± 10 mmHg; 120 ± 14 and 80 ± 11 mmHg, respectively). The real-EDV showed no significant difference between these two groups, but the real-ESV and real-EF showed significant differences between these two groups (69.4 ± 9.3 and 70.6 ± 8.9 mL/m²; 23.5 ± 5.7 and 25.6 ± 3.7 mL/m², 66.5 ± 5.1% and 63.5 ± 4.6%, respectively).

Conclusion

The difference of heart rate is significantly influenced by gender and the dosage of propranolol. Propranolol will also increase the ESV, which contributes to a decreased EF, while the SBP, DBP and EDV are not statistically changed.     

Causes of interscan variability of coronary artery calcium measurements at electron-beam CT

RATIONALE AND OBJECTIVES: The authors performed this study to investigate the causes of interscan variability of coronary artery calcium measurements at electron-beam computed tomography (CT). MATERIALS AND METHODS: Two sets of electron-beam CT scans were obtained in 298 consecutive patients who underwent electron-beam CT to screen for coronary artery calcium. Interscan variations of coronary artery calcium characteristics and the effects of heart rate, electrocardiographic (ECG) triggering method, image noise, and coronary motion on interscan variability were analyzed. RESULTS: The interscan mean variabilities were 21.6% (median, 11.7%) and 17.8% (median, 10.8%) with the Agatston and volumetric score, respectively (P < .01). Variability decreased with increasing calcification score (34.6% for a score of 11-50 and 9.4% for a score of 400-1,000, P < .0001). The absolute difference in Agatston score between scans was 44.1 +/- 95.6. The correlation coefficient between the first and second sets of scans was 0.99 (P < .0001). Lower interscan variability was found in younger patients (<60 years), patients with stable heart rates (heart rate changing less than 10 beats per minute during scanning), patients with no visible coronary motion, and those with an optimal ECG triggering method (P < .05 for all). Results of multivariate logistic analysis showed that changes in calcium volume, mean attenuation, and peak attenuation were significant predictors of interscan variability and caused the interscan variations of the coronary artery calcium measurements (r2 = 0.83, P < .0001). CONCLUSION: Coronary calcification at electron-beam CT varies from scan to scan. Volumetric scoring and optimal ECG triggering should be used to reduce interscan variability. Baseline calcium score and interscan variability must be considered in the evaluation of calcium progression.