| Given the technical limitations of conventional CT scanners and the physiological characteristics of pulmonary perfusion, the goal of this work was to assess the feasibility of measuring regional lung perfusion with a conventional CT scanner. A variety of theoretical and experimental work was undertaken to address specific difficulties encountered in such a measurement.; Seventeen patients participated in a study to assess the reliability of an assisted breath-hold technique to reduce respiratory motion artifacts. For the majority of these patients, respiratory motion was reduced from 1.7 cm to 0.4 cm when using the assisted breath-hold technique. Because the injection protocol in a functional study requires that a highly concentrated pulse of the contrast be delivered in a very short time, the relationship between contrast concentration and CT number must be carefully studied. Therefore, this relationship was theoretically and experimentally examined. The linearity between CT number and contrast concentration was found to falter when: (1) x-rays become beam-hardened in the contrast; (2) there are large variations in concentration within the CT scan-time, and; (3) the contrast passes through the imaging plane rapidly. Streaking artifacts emanating from vessels containing the contrast were found to perturb the CT number in the surrounding vessel. This is primarily due to the time changes in density in the vessel, rather than beam-hardening. To obtain reliable perfusion estimates in the presence of noisy data, a non-model based deconvolution method that uses the input, tissue and output signals of blood flow was developed. This method was shown to be more reliable than more conventional methods of deconvolution. High signal-to-noise ratios in the lung were obtained when using a low tube-energy (100 or 120 kVp) and large slice thickness (0.5–1.0 cm).; A pilot study to measure regional lung perfusion on a cancer patient was successfully performed. This work demonstrates the first reported measurement of regional lung perfusion using a conventional CT scanner. Because conventional scanners are accessible in most clinics and this technique requires only minor modifications to these scanners, there is great potential in the use of functional CT in healthy and diseased lung. |
