Voxel-wise quantification of myocardial blood flow with cardiovascular magnetic resonance: effect of variations in methodology and validation with positron emission tomography.

BACKGROUND: Quantitative assessment of myocardial blood flow (MBF) from cardiovascular magnetic resonance (CMR) perfusion images appears to offer advantages over qualitative assessment. Currently however, clinical translation is lacking, at least in part due to considerable disparity in quantification methodology. The aim of this study was to evaluate the effect of common methodological differences in CMR voxel-wise measurement of MBF, using position emission tomography (PET) as external validation. METHODS: Eighteen subjects, including 9 with significant coronary artery disease (CAD) and 9 healthy volunteers prospectively underwent perfusion CMR. Comparison was made between MBF quantified using: 1. Calculated contrast agent concentration curves (to correct for signal saturation) versus raw signal intensity curves; 2. Mid-ventricular versus basal-ventricular short-axis arterial input function (AIF) extraction; 3. Three different deconvolution approaches; Fermi function parameterization, truncated singular value decomposition (TSVD) and first-order Tikhonov regularization with b-splines. CAD patients also prospectively underwent rubidium-82 PET (median interval 7 days). RESULTS: MBF was significantly higher when calculated using signal intensity compared to contrast agent concentration curves, and when the AIF was extracted from mid- compared to basal-ventricular images. MBF did not differ significantly between Fermi and Tikhonov, or between Fermi and TVSD deconvolution methods although there was a small difference between TSVD and Tikhonov (0.06 mL/min/g). Agreement between all deconvolution methods was high. MBF derived using each CMR deconvolution method showed a significant linear relationship (p<0.001) with PET-derived MBF however each method underestimated MBF compared to PET (by 0.19 to 0.35 mL/min/g). CONCLUSIONS: Variations in more complex methodological factors such as deconvolution method have no greater effect on estimated MBF than simple factors such as AIF location and observer variability. Standardization of the quantification process will aid comparison between studies and may help CMR MBF quantification enter clinical use.

Is a target culture in health care always compatible with efficient use of resources? A cost-effectiveness analysis of an intervention to achieve thrombolysis targets.

BACKGROUND: The UK government has attempted to improve the quality of health care in the National Health Service and minimize geographical variations in quality by imposing targets in certain areas of health care. The measures taken by local health economies to achieve these targets have not before been subjected to cost-effectiveness analysis. We have assessed the cost effectiveness of an intervention designed to achieve thrombolysis time targets. METHODS: In the setting of a single district general hospital in England, we audited local pain-to-needle (PTN) and door-to-needle (DTN) times, before and after a pounds 208,000 (Euro 310,000, dollar 370,000) annual expenditure to improve performance against government targets. The intervention included the recruitment of additional nursing time in the Accident & Emergency Department and the use of a single bolus thrombolytic agent for all patients with ST elevation myocardial infarction. An economic evaluation was performed, based on the expected number of additional lives saved, extrapolated from a meta-analysis of previous thrombolysis trials. RESULTS: The intervention reduced mean DTN time from 37.6 +/- 5.9 minutes (mean +/- SEM) to 27.6 +/- 3.6 minutes (p = 0.06). The cost per life saved was pounds 3,423 +/- 850 (Euro 5,100,000, dollar 6,100,000), the cost per life year gained was pounds 222,184 (Euro 330,000, dollar 390,000) and the cost per quality-adjusted life year (QALY) gained was pounds 246,871 (Euro 370,000, dollar 440,000). CONCLUSION: Although moderately successful at improving performance against government targets, this intervention to promote rapid thrombolysis proved to be an inefficient use of health-care resources. Strict government targets in health care may not always lead to efficient targeting of resources.