***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 Are meta-analyses the brave new world , or are the critics of such combined analyses right to say that the biases inherent in clinical trials make them uncombinable ? Negative trials are often unreported , and hence can be missed by meta-analysts . And how much heterogeneity between trials is acceptable ? A recent major criticism is that large r and omised trials do not always agree with a prior meta- analysis . Neither individual trials nor meta-analyses , reporting as they do on population effects , tell how to treat the individual patient . Here we take a more rounded approach to meta-analyses , arguing that their strengths outweigh their weaknesses , although the latter must not be brushed aside 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 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 OBJECTIVE The purpose of this study was to investigate the diagnostic accuracy of dual- source CT coronary angiography with prospect i ve ECG triggering compared with catheter angiography and to determine the influence of vessel wall calcifications . SUBJECTS AND METHODS One hundred consecutive patients ( 42 women and 58 men ; mean age , 65.8 + /- 6.5 years ) with a sinus rhythm and heart rates < 70 beats per minute were included . Two independent , blinded readers classified coronary artery segments as being of diagnostic or nondiagnostic image quality and assessed each segment with diagnostic image quality for the presence of significant coronary stenoses . Nondiagnostic segments were excluded from analysis . Sensitivity , specificity , positive predictive value ( PPV ) , and negative predictive value ( NPV ) were calculated for all patients and for the subgroup of patients with a low or high calcium score ( group A , median Agatston score < 316 ; group B , > or = 316 ) . Catheter angiography was used as the reference st and ard . Effective radiation dose values were calculated . RESULTS In 89 of 100 patients ( 89 % ) , 1,462 of 1,524 coronary segments ( 96 % ) were depicted with diagnostic image quality . The overall sensitivity , specificity , PPV , and NPV were 98 % , 99 % , 95 % , and 100 % , respectively . The rate of segments with nondiagnostic image quality was significantly higher ( p < 0.001 ) in group B compared with group A. In group A , sensitivity , specificity , PPV , and NPV were 99 % , 99 % , 94 % , and 100 % , respectively , and in group B , 98 % , 99 % , 94 % , and 99 % , respectively , with no significant differences between the groups . The average effective radiation dose was 2.6 + /- 0.8 mSv ( range , 1.2 - 4.4 mSv ) . CONCLUSION Dual- source CT coronary angiography with use of prospect i ve ECG triggering performs accurately in the assessment of coronary artery disease at low radiation doses . Diagnostic accuracy remains high despite the presence of heavy calcifications but is associated with an increased rate of nondiagnostic segments AIMS To assess the diagnostic accuracy of 256-row computed tomographic angiography ( CTA ) in patients with suspected coronary artery disease ( CAD ) . Non-invasive imaging of the coronary artery by CTA has increasingly been used in recent years . The accuracy of 256-row CTA has not yet been studied . We sought to assess the accuracy of 256-row CTA compared with invasive coronary angiography ( ICA ) in the diagnosis and assessment of CAD . METHODS AND RESULTS We prospect ively evaluated 104 consecutive individuals who accepted CTA and then underwent ICA .  The presence of stenosis > or = 50 % was considered obstructive . The diagnostic accuracy of CTA for detecting obstructive stenosis was compared with that of ICA . The area under the receiver-operating-characteristic curve ( AUC ) was used to evaluate the diagnostic accuracy of CTA relative to ICA .  A total of 86 patients had obstructive CAD . The patient-based analysis of CTA for detecting stenosis > or = 50 % according to ICA revealed an AUC of 0.744 [ 95 % confidence interval ( CI ) , 0.572 - 0.916 ] , with a sensitivity of 98.8 % , a specificity of 50 % , a positive predictive value ( PPV ) of 92.4 % , and a negative predictive value ( NPV ) of 87.5 % . The segment-based analysis revealed an AUC of 0.915 ( 95 % CI , 0.847 - 0.982 ) , with a sensitivity of 93.5 % , a specificity of 95 % , a PPV of 77.6 % , and an NPV of 98.7 % . The vessel-based analysis revealed an AUC of 0.887 ( 95 % CI , 0.808 - 0.966 ) , with a sensitivity of 94.3 % , a specificity of 87.3 % , a PPV of 82.7 % , and an NPV of 95.9 % . CONCLUSION 256-Row CTA is a highly sensitive test of CAD and has a high predictive value . 256-Row CTA may be a potential alternative to detect coronary artery stenosis and rule out CAD in suspected patients CONTEXT Cardiac computed tomography angiography ( CCTA ) can accurately diagnose coronary artery disease , but radiation dose from this procedure is of concern . OBJECTIVES To determine whether a collaborative radiation dose-reduction program would be associated with reduced radiation dose in patients undergoing CCTA in a statewide registry over a 1-year period and to define its effect on image quality . DESIGN , SETTING , AND PATIENTS A prospect i ve , controlled , nonr and omized study conducted during a control period ( July-August 2007 ) , an intervention period ( September 2007-April 2008 ) , and a follow-up period ( May-June 2008 ) at 15 hospital imaging centers participating in the Advanced Cardiovascular Imaging Consortium in Michigan , which included small community hospitals and large academic medical centers . A total of 4995 sequential patients undergoing CCTA for suspected coronary artery disease were enrolled ; 4862 patients ( 97.3 % ) had complete radiation data for analysis . INTERVENTION A best- practice CCTA scan model was used , which included minimized scan range , heart rate reduction , electrocardiographic-gated tube current modulation , and reduced tube voltage in suitable patients . MAIN OUTCOME MEASURES Primary outcomes included dose-length product and effective radiation dose from all phases of the CCTA scan . Secondary outcomes were image quality assessed by a 4-point scale ( 1 indicated excellent ; 2 , good ; 3 , adequate ; and 4 , nondiagnostic ) and frequency of diagnostic- quality scans . RESULTS Compared with the control period , patients ' estimated median radiation dose in the follow-up period was reduced by 53.3 % ( dose-length product decreased from 1493 mGy x cm [ interquartile range { IQR } , 855 - 1823 mGy x cm ] to 697 mGy x cm [ IQR , 407 - 1163 mGy x cm ] ; P < .001 ) and effective dose from 21 mSv ( IQR , 12 - 26 mSv ) to 10 mSv ( IQR , 6 - 16 mSv ) ( P < .001 ) . The greatest reduction in dose occurred at low-volume sites . There were no significant changes in median image quality assessment during the control period compared with the follow-up period ( median image quality of 2 [ images rated as good ] vs median image quality of 
    Output:
    
Multislice CT coronary angiography with prospect i ve ECG-gating leads to a significant reduction of radiation dose when compared to that of retrospective ECG-gating , while offering comparable image quality and diagnostic value