Why are some CCTA scans ineligible for FFR-CT analysis?

By Abraham Kim, AuntMinnie.com staff writer

July 29, 2019 -- A significant proportion of coronary CT angiography (CCTA) scans has been deemed ineligible for analysis with fractional flow reserve CT (FFR-CT) in recent studies. An international team of researchers investigated the underlying causes behind this issue in an article published online July 23 in Radiology.

FFR-CT enables clinicians to calculate fluid dynamics within the heart as a possible indicator of coronary artery disease (CAD). The technique is far less invasive than conventional FFR, in which a guidewire is threaded via a catheter into a coronary artery to measure blood pressure and flow.

Prior research has demonstrated numerous advantages of integrating FFR-CT into the assessment of CAD, including improved diagnostic accuracy and risk prediction. More specifically, FFR-CT can help reduce the number of patients unnecessarily referred for invasive coronary angiography, noted co-first authors Drs. Gianluca Pontone, PhD, from Centro Cardiologico Monzino in Italy and Jonathan Weir-McCall of the University of Cambridge in the U.K. and colleagues.

But CCTA images must be of adequate quality to be analyzed with FFR-CT software -- and many images are falling short. For instance, as much as 33% of CCTA scans in the Prospective Multicenter Imaging Study for Evaluation of Chest Pain (PROMISE) trial were ineligible for FFR-CT analysis, prompting concern among clinicians.

To better understand this setback, Pontone, Weir-McCall, and colleagues acquired CCTA scans of 2,778 patients as part of the Assessing Diagnostic Value of Noninvasive FFR-CT in Coronary Care (ADVANCE) registry. They also obtained the CCTA scans of 10,416 cases that were submitted for FFR-CT analysis at one of 76 distinct medical centers across the globe. The researchers searched for the chief factors contributing to the rejection of CCTA scans for FFR-CT analysis in these two groups of patients.

In total, the researchers noted an FFR-CT rejection rate of 2.9% in the ADVANCE registry and 8.6% for the clinical cohort. They found that the main reason for the rejection of CCTA scans was inadequate image quality, primarily due to motion artifacts, which were present in 78% of the CCTA scans in the ADVANCE registry and 64% in the clinical cohort.

Through multivariable analysis, the researchers additionally uncovered several factors that were independent predictors of FFR-CT rejection: CCTA scans with a relatively large temporal resolution and slice thickness, as well as scans of patients with a relatively fast heart rate.

Factors affecting eligibility of CCTA scans for FFR-CT analysis
  Eligible for FFR-CT Ineligible for FFR-CT
ADVANCE registry Clinical cohort ADVANCE registry Clinical cohort
CCTA slice thickness 0.64 mm 0.63 mm 0.67 mm 0.65 mm
CCTA temporal resolution 106 msec 119 msec 119 msec 130 msec
Patient heart rate 60 beats per minute 60 beats per minute 63 beats per minute 65 beats per minute
The differences between eligible and ineligible scans were statistically significant.

Furthermore, the researchers found that the increased use of dual-source CT scanners and wide-coverage single-source CT scanners was associated with fewer rejected CCTA scans. Clinicians used these technologies for roughly 85% of CCTA exams in the ADVANCE registry and 79% in the clinical cohort, compared with only 17% in the PROMISE study.

The findings suggest that clinicians should be able to use nearly all CCTA scans for FFR-CT analysis with simple adjustments to scanning protocols, such as minimizing image slice thickness, controlling patient heart rate, and using dual-source or wide-coverage single-source CT scanners.

"Although a certain degree of [selection] bias may not be excluded, the low rejection rate of FFR-CT in the control cohort is encouraging for widespread use of FFR-CT in patients with CAD," Dr. Hajime Sakuma, PhD, of Mie University Hospital in Japan wrote in an accompanying editorial.


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