Circ: 128-slice CT may cut rad dose six-fold compared to older generation scanners

Use of a 128-slice dual source CT led to ultrafast imaging of the entire heart and reduced radiation exposure significantly when compared to a shutter-mode dynamic myocardial perfusion protocol with alternating table positions, according to a study published Aug. 23 in Circulation: Heart Failure. Adenosine stress myocardial CT perfusion (CTP) imaging with the 128-slice technology can accurately detect both myocardial ischemia and coronary stenosis.

“Coronary computed tomography angiography (CTA) enables accurate anatomic evaluation of coronary artery stenosis, however lacking information about hemodynamic significance,” Gudrun Feuchtner, MD, of the University Hospital Zurich, and colleagues wrote. “This limitation often necessitates additional testing for reversible myocardial ischemia, as coronary revascularization by percutaneous coronary intervention or coronary artery bypass graft (CAGB) surgery is indicated in the presence of significant ischemia.”

During the study, Feuchtner et al compared 128-slice myocardial CTP imaging (Somatom Definition Flash, Siemens Healthcare) with adenosine vasodilator stress using a high-pitch mode to cardiac MR. The study included 39 patients with intermediate-to-high coronary risk who underwent adenosine stress 128-slice dual source myocardial CTP. Among the 39 patients, 30 also underwent adenosine stress cardiac MR and 25 patients had invasive angiography within six weeks of CTP.

The CTP protocol was as follows:

• Adenosine stress CTP using a high-pitch factor ECT-synchronized spiral mode; and

• Rest CTP/coronary CTA using either high-pitch or prospective ECG-triggering.

The total effective radiation dose when the two-step myocardial CTP protocol was used was reported to be 2.5 mSv, mean scan time for stress CTP was 0.31 seconds and scan length was 14.3 cm. Meanwhile, the effective radiation dose for stress CTP was 0.93 mSv and for rest-CTP was 1.59 mSv.

The authors reported that during the detection of myocardial perfusion defects during adenosine, stress CTP had a sensitivity of 78 percent, a specificity of 87 percent, a positive predictive value of 83 percent and a negative predictive value of 84 percent per segment. Additionally, the accuracy of CTP to detect reversible defects on CT during adenosine had a 68 percent sensitivity, 88 percent specificity, a positive predictive value of 72 percent and a negative predictive value of 85 percent.

The 128-slice CT had 90 percent accuracy in detecting significant blockages and accuracy improved to 95 percent when added to CT perfusion.

“This new technique, allows for ultrafast imaging of the entire heart within the mid- to end-diastole of only one cardiac cycle,” Feuchtner et al wrote. “It resulted in about six-fold lower radiation dose as compared to adenosine stress CT MPI imaging using first generation 64-slice duel slice CT (accumulated effective radiation exposure of 12.7 mSv), and resulted in 10-fold lower radiation dose as compared to the “shuttle-mode” dynamic myocardial perfusion protocol with alternating table positions (mean, 9.6mSv x 2 for each acquisition).”

The two potential clinical applications are:

• Patients with high coronary risk profile—coronary artery disease (CAD)—or those with a high calcium score;
• Patients exhibiting intermediate (50 to 70 percent) coronary stenosis on coronary CTA or in patients with suspected in-stent restenosis. CTP could determine hemodynamic significance of the lesions.

“This can have important implications for cost savings and efficiency as two studies are done in one setting,” concluded Ricardo C. Cury, MD, co-author of the study and chair of radiology at Baptist Health South Florida in Coral Gables, Fla.