An automatic calibration approach for left ventricular volume assessment

The development of interventional procedures in the catheterisation laboratory drives the introduction of simple, fast and accurate quantification methods. Quantification is used to evaluate the volume of the left ventricle but also for choosing the size of a balloon or a stent during the percutaneous coronary angioplasty procedure. The objective of the calibration procedure is to establish the relation between the true size of the analyzed organ and its apparent size in the image. This calibration step aims at measuring the pixel size in mm. Traditional approach measures a known object on the image, but suffers from several limitations and constraints; in particular, the size of the reference object is often not exactly known. Besides, the therapeutic procedures are done in the continuity of the diagnosis and the physician has a very little amount of time to spend on the determination of the quantitative information like the chosen reference size. A new approach has been proposed [1], allowed by the introduction of the flat-panel technology and modern positioning systems. With the absence of distortion in the image and accurate knowledge of the system geometry, a model can be used to automatically identify the calibration factor using an additional input provided by the operator: the target organ height above the table top. The objective of our study was to estimate this input parameter in the particular case of the Left Ventricle (LV) volume angiographic computation.