Anatomy of an Emerging Diagnostic Test

Estimation of absolute myocardial blood flow during first-pass MR perfusion imaging using a dual-bolus injection technique: comparison to single-bolus injection method

PURPOSE

To compare the dual-bolus to single-bolus quantitative first-pass magnetic resonance myocardial perfusion imaging for estimation of absolute myocardial blood flow (MBF).

MATERIALS AND METHODS

Dogs had local hyperemia of MBF in the left anterior descending (LAD) coronary artery (intracoronary adenosine). Animals (n = 6) had sequential single- and dual-bolus perfusion studies with microsphere determination of absolute MBF. Perfusion imaging was performed using a saturation-recovery gradient-echo sequence. Absolute MBF was by Fermi function deconvolution and compared to transmural, endocardial, and epicardial microsphere values in the same region of interest (ROI).

RESULTS

Signal and contrast were significantly higher for the dual-bolus perfusion images. The correlation with MBF by microspheres was r = 0.94 for the dual-bolus method and r = 0.91 for the single-bolus method. There was no significant difference between MRI and microsphere MBF values for control or hyperemic zones for transmural segments for either technique. When the ROI was reduced to define endocardial and epicardial zones, single-bolus MR first-pass imaging significantly overestimated MBF and had a significantly larger absolute error vs. microspheres when compared to dual-bolus perfusion.

CONCLUSION

Both single-bolus and dual-bolus perfusion methods correlate closely with MBF but the signal and contrast of the dual-bolus images are greater. With smaller nontransmural ROIs where signal is reduced, the dual-bolus method appeared to provide slightly more accurate results.

Analytic approaches to establish the diagnostic accuracy of coronary computed tomography angiography as a tool for clinical decision making

Although 64-slice multidetector coronary computed tomography angiography (CTA) has been reported to have excellent test characteristics for the detection of significant coronary artery disease, current analytic approaches may not appropriately reflect the process of clinical decision making. Thirty-seven patients (29 men; mean age 63 +/- 11 years) who underwent coronary CTA for clinical indications followed by invasive coronary angiography within 4 weeks were studied. Computed tomography angiograms were analyzed independently for the presence of significant coronary artery stenosis (>or=50% luminal narrowing) by 2 observers blinded to invasive coronary angiographic results. The diagnostic test performance of coronary CTA was determined with and without inclusion of unassessable segments. Because stenosis could not be excluded in unassessable segments, these segments were counted as positive for stenosis. Sensitivity, specificity, and positive (PPV) and negative predictive values of CTA for detecting significant stenoses on assessable segments were 85% (51 of 60, 95% confidence interval [CI] 76% to 94%), 99% (414 of 416, 95% CI 99 to 100), 96% (95% CI 51 of 53), and 98% (95% CI 414 of 423), respectively. Overall, 13% of coronary segments (70 of 546) were not assessable using CTA (heavy calcium in 48 segments). By including these segments, PPV decreased from 96% to 60% (74 of 123), whereas sensitivity improved from 85% to 89% (95% CI 74 of 83). In conclusion, the clinical utility of coronary CTA may be limited by a low PPV in patients with a high prevalence of coronary artery disease.

Applications of multislice computed tomography in coronary artery disease

Multislice computed tomography (MSCT) provides high accuracy for noninvasive assessment of coronary artery disease (CAD). The introduction of the latest computed tomography (CT) technology allows comprehensive evaluation of various aspects of CAD, including the coronary calcium score, coronary artery stenoses, bypass patency, and myocardial function. Other applications, such as plaque characterization, first-pass perfusion imaging, and viability imaging using delayed contrast enhancement, are still under development and may demonstrate clinical utility in the future. Further improvements in CT hardware and imaging protocols are expected that may result in improved coronary artery imaging, new applications, and a significant reduction of radiation dose.

The clinical value of a negative multi-detector computed tomographic angiography in patients suspected of coronary artery disease: A meta-analysis

The aim of this meta-analysis was to calculate the sensitivity of contrast-enhanced multi-detector computed tomography (MDCT) compared with coronary angiography (CAG) in incident patients suspected of coronary artery disease (CAD). We searched PubMed, Embase, bibliographies of original papers and reviews to identify original papers including > or =20 patients. Two independent reviewers selected papers and judged eligible papers on quality. Heterogeneity was assessed and homogeneous subgroups were pooled. Of the 15 included studies, ten provided moderately homogeneous patient-based analyses with absolute diagnostic numbers (n = 630 patients). Pooled sensitivity was 89% (95% confidence interval: 85-92%). Scanners with 16 detectors (n = 4) had higher sensitivities (pooled sensitivity: 91%) than four-detector scanners (n = 6; pooling not possible due to heterogeneity). Seven studies reported sensitivity for a proximal stenosis, but different definitions were used making pooling impossible; sensitivities ranged from 75 to 100%. The sensitivity of four- and 16-detector MDCT is not sufficient to rule out any stenosis in patients suspected of CAD. No conclusions can be drawn with respect to the sensitivity for clinically relevant or proximal stenoses.

Prognosis of negative adenosine stress magnetic resonance in patients presenting to an emergency department with chest pain

OBJECTIVES

This study was designed to determine the diagnostic value of adenosine cardiac magnetic resonance (CMR) in troponin-negative patients with chest pain.

BACKGROUND

We hypothesized that adenosine CMR could determine which troponin-negative patients with chest pain in an emergency department have coronary artery disease (CAD) or future adverse cardiac events.

METHODS

Adenosine stress CMR was performed on 135 patients who presented to the emergency department with chest pain and had acute myocardial infarction (MI) excluded by troponin-I. The main study outcome was detecting any evidence of significant CAD. Patients were contacted at one year to determine the incidence of significant CAD defined as coronary artery stenosis >50% on angiography, abnormal correlative stress test, new MI, or death.

RESULTS

Adenosine perfusion abnormalities had 100% sensitivity and 93% specificity as the single most accurate component of the CMR examination. Both cardiac risk factors and CMR were significant in Kaplan-Meier analysis (log-rank test, p = 0.0006 and p < 0.0001, respectively). However, an abnormal CMR added significant prognostic value in predicting future diagnosis of CAD, MI, or death over clinical risk factors. In receiver operator curve analysis, adenosine CMR was a more accurate predictor than cardiac risk factors (p < 0.002).

CONCLUSIONS

In patients with chest pain who had MI excluded by troponin-I and non-diagnostic electrocardiograms, an adenosine CMR examination predicted with high sensitivity and specificity which patients had significant CAD during one-year follow-up. Furthermore, no patients with a normal adenosine CMR study had a subsequent diagnosis of CAD or an adverse outcome.