[New developments in parameter-oriented roentgen densitometry perfusion analysis within the scope of heart catheter studies].

Abstract

X-ray densitometric evaluation of digital subtraction coronary arteriograms allows a qualitative and quantitative detection of contrast medium propagation through the epicardial coronary arteries, the capillary system and the coronary venous system. So-called "time-density-curves" (TDCs) can be generated following Lambert-Beer's law similar to indicator dilution curves by using contrast medium as the indicator. Several time and density parameters can be derived from these TDCs, which are related to local myocardial perfusion. Different animal validation studies have shown the applicability of this concept for in-vivo evaluation of coronary blood flow and myocardial perfusion. Nevertheless, absolute measurement of volumetric coronary blood flow or myocardial perfusion failed. Therefore, relative changes in coronary blood flow or myocardial perfusion in response to pharmacologically induced maximum hyperemia were measured and coronary or myocardial perfusion reserve was calculated as the ratio of hyperemic flow or perfusion divided by baseline values. Despite theoretical attractions for an application during routine cardiac catheterization, this densitometric approach did not get a wide acceptance. Primary reason for this limited use in specialized centers was the time consuming process of densitometric evaluation of the subtraction coronary arteriograms, which require digital cine angiography and necessitates enormous computer hard ware. This main limitation has been overcome since more powerful computer hard ware (processor speed, hard disk space, digitization boards) has become rapidly available during the last years at more moderate pricing and digital techniques today are state of the art in cardiac catheterization laboratories. In addition, soft ware program packages allowed an automatization of the digitization and densitometric evaluation process. These programs include ECG triggered cine image digitization with improved temporal resolution, semiautomatic definition of regions-of-interest including definition of reference regions-of-interest for the detection of background density changes and quality-controlled densitometric parameter analysis. This progress made an application during routine cardiac catheterization feasible. In animal validation studies this improved X-ray densitometric approach for evaluation of local myocardial perfusion was validated versus colour-coded microsphere techniques. The time parameter "rise time", defined as the time from the start of local contrast medium induced density change to its maximum revealed a close correlation (r2 = 0.965) to the results of the microsphere technique over a wide range of perfusion. We have applied this technique before and after coronary interventions such as balloon angioplasty and stenting. Results documented an improvement of poststenotic myocardial perfusion reserve immediately after coronary balloon angioplasty and an additional improvement after adjunct coronary stenting. Only after stenting but usually not after coronary balloon angioplasty alone poststenotic myocardial perfusion reserve gained the intraindividual reference level, measured in a perfusion bed supplied by an epicardial coronary artery without stenoses. These results documented the functional benefit of coronary stenting on poststenotic myocardial perfusion in addition to the well known morphologic benefit with the creation of a larger and more circular conduit.