***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: The goal of our study was to compare a prospect i ve triggering ( PT ) CT technique with retrospectively gated ( RG ) CT techniques in coronary computed tomographic angiograms ( CCTA ) with respect to image quality and radiation dose . Sixty consecutive patients were enrolled . CCTAs using the RG technique were obtained with a dual- source 64-slice CT system in 40 patients , using ECG-triggered tube current modulation , with either a broad pulsing window at 30–80 % of the RR interval ( group RGb , 20 patients , heart rate > 70 bpm ) or a small pulsing window at 70 % ( group RGs , 20 patients , heart rate < 70 bpm ) . The other 20 patients underwent CCTA using the PT technique on a 128-slice CT system ( group PT , heart rate < 70 bpm ) . All images were evaluated by two observers for quality on a three-point scale , with 1 being excellent and 3 being insufficient . The effective radiation dose was calculated for each patient . The average image quality score was 1.5 ± 0.6 for PT , 1.35 ± 0.5 for RGs and 1.65 ± 0.5 for RGb . The mean effective dose for RGb was 9 ± 4 mSv , for RGs 7 ± 3 mSv and for PT 3 ± 1 mSv . This represents a 57 % dose reduction for PT compared with RGs and a 67 % dose reduction for PT compared with RGb . In conclusion , in selected patients CCTA with the PT technique offers adequate image quality with a significantly lower radiation dose compared with CCTA using RG techniques OBJECTIVE To compare , in patients with suspicion of coronary artery disease ( CAD ) and low heart rates , image quality , diagnostic performance , and radiation dose values of prospect ively and retrospectively electrocardiography (ECG)-gated dual- source computed tomography coronary angiography ( CTCA ) for the diagnosis of significant coronary stenoses . MATERIAL S AND METHODS Two-hundred consecutive patients with heart rates ≤70 bpm were retrospectively enrolled ; 100 patients undergoing prospect ively ECG-gated CTCA ( group 1 ) and 100 patients undergoing retrospectively-gated CTCA ( group 2 ) . Coronary artery segments were assessed for image quality and significant luminal diameter narrowing . Sensitivity , specificity , positive predictive values ( PPV ) , negative predictive values ( NPV ) , and accuracy of both CTCA groups were determined using conventional catheter angiography ( CCA ) as reference st and ard . Radiation dose values were calculated . RESULTS Both groups were comparable regarding gender , body weight , cardiovascular risk profile , severity of CAD , mean heart rate , heart rate variability , and Agatston score ( all p>0.05 ) . There was no significant difference in the rate of non-assessable coronary segments between group 1 ( 1.6 % , 24/1404 ) and group 2 ( 1.4 % , 19/1385 ; p=0.77 ) ; non-diagnostic image quality was significantly ( p<0.001 ) more often attributed to stair step artifacts in group 1 . Segment-based sensitivity , specificity , PPV , NPV , and accuracy were 98 % , 98 % , 88 % , 100 % , and 100 % among group 1 ; 96 % , 99 % , 90 % , 100 % , and 98 % among group 2 , respectively . Parameters of diagnostic performance were similar ( all p>0.05 ) . Mean effective radiation dose  of prospect ively ECG-gated CTCA ( 2.2±0.4 mSv ) was significantly ( p<0.0001 ) smaller than that of retrospectively ECG-gated CTCA ( 8.1±0.6 mSv ) . CONCLUSION Prospect ively ECG-gated CTCA yields similar image quality , performs as accurately as retrospectively ECG-gated CTCA in patients having heart rates ≤70 bpm while being associated with a lower mean effective radiation dose BACKGROUND Prospect ively gated coronary computed tomographic angiography ( CCTA ) with dual- source CT allows substantial reduction of radiation exposure but requires prospect i ve single-phase selection and assessment of likelihood of adequate image quality . OBJECTIVE We developed and tested the model for predicting success of prospect ively gated CCTA . METHODS  Retrospectively gated CCTA was acquired with dual- source CT in 162 patients . Two cardiologists assessed by consensus whether diagnostic quality images could have been obtained in a single predefined phase , 70 % of R-R interval ( 70P ) , thereby identifying patients in whom a prospect ively gated scan at 70P would have been successful . Logistic regression models were built with and without a coronary calcium scan . The obtained criteria were applied on 42 additional patients . RESULTS By logistic regression , heart rate before CCTA of > or=70 beats/min , maximal heart rate variation before CCTA of > or=10 beats/min , coronary calcium score > or= 400 U , and body mass index ( in kg/m(2 ) ) > or= 30 were independent predictors of unsuccessful prospect ively gated CCTA using 70P . Excluding coronary calcium score from the model , these same variables in addition to age > 65 years were found to be predictors of unsuccessful prospect ively gated CCTA . Applying this model to 42 additional patients , using prospect i ve gating , only 5 segments in 4 patients were nondiagnostic . Mean radiation dose for prospect ively gated CCTA was 2.2 + /- 0.8 mSv . CONCLUSION Prospect ively gated CCTA with dual- source CT can be successfully implemented with consideration of prescan heart rate , heart rate variability , body mass index , and coronary calcium score OBJECTIVES The aim of this study was to compare the diagnostic performance of multidetector computed tomography ( MDCT ) with prospect i ve electrocardiogram ( ECG ) triggering versus retrospective ECG triggering . BACKGROUND MDCT allows the noninvasive visualization of the coronary arteries . However , radiation exposure is a reason for concern . METHODS One hundred eighty consecutive patients scheduled for invasive coronary angiography were enrolled in this study . Twenty patients were excluded due to contraindications to sustain MDCT .  Of the 160 remaining patients , 80 were studied with MDCT with prospect i ve ECG triggering ( Group 1 ) and 80 with a retrospective ECG triggering ( Group 2 ) . The individual radiation dose exposure was estimated . RESULTS In nonstented segments , the evaluability of Groups 1 and 2 was 96 % versus 97 % , respectively ( p = 0.05 ) , the accuracy in segment-based model was 93 % versus 96 % , respectively ( p < 0.05 ) including diagnostic segments and 91 % versus 94 % , respectively ( p < 0.01 ) including all segments , whereas the accuracy in a patient-based model was 98 % in both groups . In stented segments the evaluability in Groups 1 and 2 was 92 % versus 94 % , respectively , and the accuracy was 93 % versus 92 % , respectively , including diagnostic stented segments and 90 % versus 89 % , respectively , including all stented segments . Group 1 presented lower radiation dose compared with Group 2 ( 5.7 + /- 1.5 mSv vs. 20.5 + /- 4.3 mSv , p < 0.01 ) . CONCLUSIONS Prospect i ve ECG-triggering computed tomography allows an accurate detection of coronary stenosis , despite a slight reduction of diagnostic performance , with a low radiation dose With the advent of multislice CT more than a decade ago , multislice CT angiography has demonstrated a huge potential in the less invasive imaging of cardiovascular disease , especially in the diagnosis of coronary artery disease . The diagnostic accuracy of multislice CT angiography has been significantly augmented with the rapid technical developments ranging from the initial 4-slice , to the current 64-slice and 256 and 320-slice CT scanners . This is mainly demonstrated by the improved spatial and temporal resolution when compared to the earlier type of CT scanners . Traditionally , multislice CT angiography is acquired with retrospective ECG-gating with acquisition of volume data at the expense of increased radiation dose , since data is acquired at the entire cardiac cycle , although not all of them are used for postprocessing or reconstructions . Recently , there is an increasing trend of utilising prospect i ve ECG-gating in cardiac imaging with latest multislice CT scanners ( 64 or more slices ) with significant reduction of radiation dose when compared to retrospective ECG-gating method . However , there is some debate as to the diagnostic value of prospect i ve ECG-gating in the diagnosis of coronary artery disease , despite its attractive ability to reduce radiation dose . This article will review the performance of retrospective ECG-gating in the diagnostic value of coronary artery disease , highlight the potential applications of prospect i ve ECG-gating , and explore the future directions of multislice CT angiography in cardiac imaging PURPOSE To evaluate the effect of a small field of view ( FOV ) for step- and -shoot coronary computed tomography angiography ( CCTA ) on craniocaudal z-coverage per scan step , image quality , and radiation exposure . METHODS 53 patients underwent prospect ively ECG-gated CCTA on a 256-slice MDCT scanner  using either a FOV > 250 mm ( group 1 , n = 29 ) or a FOV ≤ 250 mm ( group 2 , n = 24 ) . Craniocaudal z-coverage was determined on coronal multiplanar reformations . Image noise , signal-to-noise ratio , contrast-to-noise ratio , and qualitative image parameters were assessed . Radiation dose was estimated from the dose length product and was st and ardized for a scan range from the main pulmonary artery to the diaphragm in order to make both groups comparable . RESULTS Diagnostic image quality was achieved in 91.3 % of the coronary artery segments of group 1 and 89.9 % in group 2 ( p = 0.201 ) . There were no major differences in image noise , SNR , and CNR between both groups . A smaller FOV leads to an increase of craniocaudal coverage of a single CT scan step ( r = -0.879 ; p ≤ 0.001 ) . There was an increase of 23.8 % of the mean z-coverage per scanned subvolume in group 2 ( 59.9 mm vs. 48.8 mm ) . Radiation dose was significantly lower in group 2 ( 229 vs. 285 mGy cm , respectively ) . CONCLUSION The use of a small transverse FOV for step- and -shoot CCTA at a wide detector CT scanner leads to an increased z-coverage . 2 scan volumes are enough to image the cardiac anatomy . Radiation dose is decreased without negative impact on image quality Background — Surveillance conventional coronary angiography ( CCA ) is recommended 2 to 6 months after stent-supported left main coronary artery ( LMCA ) percutaneous coronary intervention due to the unpredictable occurrence of in-stent restenosis ( ISR ) , with its attendant risks . Multislice computed tomography ( MSCT ) is a promising technique for noninvasive coronary evaluation . We evaluated the diagnostic performance of high-resolution MSCT to detect ISR after stenting of the LMCA . Methods and Results — Seventy-four patients were prospect ively identified from a consecutive patient population scheduled for follow-up CCA after LMCA stenting and underwent MSCT before CCA .  Until August 2004 , a 16-slice scanner was used ( n=27 ) , but we switched to the 64-slice scanner after that period ( n=43 ) . Patients with initial heart rates > 65 bpm received β-blockers , which result ed in a mean periscan heart rate of 57±7 bpm . Among patients with technically adequate scans ( n=70 ) , MSCT correctly identified all patients with ISR ( 10 of 70 ) but misclassified 5 patients without ISR ( false-positives ) . Overall , the accuracy of MSCT for detection of angiographic ISR was 93 % . The sensitivity , specificity , and positive and negative predictive values were 100 % , 91 % , 67 % , and 100 % , respectively . When analysis was restricted to patients with stenting of the LMCA with or without extension into a single major side branch , accuracy was 98 % . When both branches of the LMCA bifurcation were stented , accuracy was 83 % . For the assessment of stent diameter and area , MSCT showed good correlation with intravascular ultrasound ( r=0.78 and 0.73 , respectively ) . An intravascular ultrasound threshold value ≥1 mm was identified to reliably detect in-stent neointima hyperplasia with MSCT . Conclusions — Current MSCT technology , in combination with optimal heart rate control , allows reliable noninvasive evaluation of selected patients after LMCA stenting . MSCT is safe to exclude left main ISR and may therefore be an acceptable first-line alternative to CCA We sought to determine the cut-off point of the average heart rate ( HR ) and HR differences in obtaining diagnostic image quality using prospect i ve electrocardiographically-triggered ( PT ) coronary computed tomographic angiography ( CCTA ) and to compare image quality and radiation dose for CCTA obtained with PT CCTA and retrospective electrocardiographically-gated ( RG ) CCTA . A total 
    Output:
    
The pooled estimates of diagnostic values were more than 90 % for patient- , vessel- and segment-based assessment s. Prospect i ve ECG-triggered CCTA results in high diagnostic accuracy and image quality , with a significantly low radiation dose