Werner Jaschke

Measurement of cardiac output by cine computed tomography

High-speed computed transmission tomography (cine CT) is a new noninvasive technique that may be useful for the rapid, accurate quantitation of cardiac function. The capability of cine CT to assess cardiac output was examined 10 mongrel dogs as an initial step in validating this method. After the dogs were anesthetized, femoral arterial pressure and pulmonary artery thermodilution catheters were inserted. After intravenous injection of a bolus of contrast medium, cine CT scans were performed in the flow mode, in which 50-ms scans were triggered electrocardiographically at end-diastole at 8 levels during sequential cardiac cycles. Scans and thermodilution measurements of cardiac output were obtained at rest and during altered hemodynamic states induced by separate infusions of dobutamine and phenylephrine. Time-density analysis was performed over the left ventricular cavity and curves were fitted to the CT flow data by gamma-variate analysis. Using the Stewart-Hamilton equation established for indicator dilution techniques, the cardiac output was calculated. The results established a direct linear correlation (r = 0.92) between cine CT cardiac output and thermodilution cardiac output over a wide range of cardiac outputs (1.5 to 6.3 liters/min). This study demonstrates that cine CT can provide a reliable estimate of cardiac output noninvasively using contrast medium as an indicator in dogs.

Flow measurements with a high-speed computed tomography scanner.

A high-speed computed tomography (CT) scanner with a scan time of 50 ms was used to measure flow in a phantom constructed to simulate both tissue and vessels. After a bolus injection of iodinated contrast medium, the phantom was scanned at a rate of up to 2 images/s. A gamma-variate curve was fit to the time-density data obtained from the inlet and outlet, as well as from the tissue-equivalent part of the phantom. Flow was then calculated using different curves and curve parameters according to the Stewart-Hamilton equation, the mean transit time, and a modification of the Sapirstein principle. Actual flow rates were assessed by timed sampling. The results demonstrated that high-speed CT can measure flow accurately by all these methods. Application of high-speed CT for flow measurements in experimental animals and patients is, therefore, promising. The limitations of each technique for clinical application are discussed.

Cine-CT measurement of cortical renal blood flow

A modified indicator-dilution technique using radiographic contrast material and a cine-CT scanner was used to measure blood flow in the renal cortex of dogs. To validate this technique. CT measurements were correlated with simultaneous measurements of flow determined by radioactive micro-spheres. Measurements were taken during euvolemic conditions and after hemorrhage. Thirty-nine measurements were compared, covering a flow range from 1 to 7 ml min−1 g−1, and a good correlation was found between the cine-CT and microsphere results (r = 0.93; p < 0.001). Additionally, cine-CT measurements were made of the mean transit time (MTT) of contrast material through the renal cortex, and the reciprocal of these MTT values was also well correlated to microsphere determined flow (r = 0.94; p < 0.001). Thus, cine-CT appears to be a promising new technique for measuring renal blood flow.

Transjugular intrahepatic portosystemic shunting (TIPS) with balloon-expandable and self-expanding stents: Technical and clinical aspects after 3 1/2 years’ experience

PurposeTo evaluate prospectively our experience with transjugular intrahepatic portosystemic shunt (TIPS) using four different metallic stents.MethodsBetween November 1991 and April 1995, 57 patients (41 men and 16 women; age 35–72 years, mean 54 years) underwent the TIPS procedure. Techniques for portal vein localization before and during TIPS were fluoroscopy, computed tomography (CT) studies, wedged hepatic venography, arterial portography, and ultrasound. After predilation we deployed balloon-expandable (n=48) and self-expanding (n=45) metallic stents. Fifteen patients underwent variceal embolization. Initial follow-up angiograms (mean 6.9 months, range 3–24 months) were obtained in 39 of these patients.ResultsFifty-three patients (93%) had successful TIPS placement. The mean decrease in portal pressure was 42.7%. Besides fluoroscopy, the most helpful techniques for portal vein localization were venography and CT. Residual stenosis (n=1) and late shortening (n=4) of Wallstents resulted in shunt dysfunction. The technical problems encountered with the Palmaz stent resulted from its lack of flexibility. We combined balloon-expandable and self-expanding stents in 12 patients. The 30-day and late follow-up (mean 11.9 months) percutaneous reintervention rates were 11.3% and 64.2%, respectively. There were no clinically significant complications related to the TIPS insertions.ConclusionAn ideal stent does not exist for TIPS, and the authors recommend combining a Palmaz stent with a flexible self-expanding stent.

A new balloon-expandable tantalum stent (Strecker-Stent) for the biliary system : preliminary experience

Placement of a balloon-expandable metallic stent (Strecker-Stent) for biliary drainage has been attempted in 30 patients. The stent was successfully implanted in 22 patients; in the remaining 8 patients, dilatation of the biliary stricture prior to stent placement was inadequate and delivery of the Strecker-Stent was, therefore, not possible. Insufficient balloon dilatation was related to the rigid nature of the stricture and to pain experienced during dilatation. During 2–9 months follow-up, 3 of 21 patients (14%) presented with reocclusion of the stented bile ducts. In all other patients, biliary drain-age remains adequate. No major complications related to stent placement were observed.

Quantitation of intracardiac shunts by cine-CT.

Quantitation of intracardiac shunts is important in the evaluation of congenital heart disease and ventricular septal defects postmyocardial infarction. Shunt detection and quantitation is currently performed by either oximetry or radionuclide angiography. Oximetry is an invasive technique and radionuclide angiography, although noninvasive, does not have sufficient spatial resolution to provide detailed anatomic information. The present study evaluated a new technique for quantitating right-to-left shunts by analysis of indicator dilution curves acquired noninvasive using cine-CT. This technique was evaluated in a phantom and in postoperative dogs with a surgically created variable shunt. The phantom model demonstrated the accuracy and reproducibility of the curve analysis algorithm, and the canine model permitted the comparison of oximetry with cine-CT for shunt quantitation. Cine-CT accurately estimated right-to-left shunt fraction when compared with oximetry (r = 0.91) and is more sensitive than oximetry in detecting small shunts. The results of this study suggest that contrast enhanced cine-CT provides a precise noninvasive technique for measuring shunt lesions in congenital and acquired heart diseases.

Spatial Resolution Analysis of Computed Tomographic Images

Methods are presented for the quantification of spatial resolution in x-ray computed tomographic (CT) images. Model-dependent methods are derived and compared with model independent methods for computation of the Modulation Transfer Function (MTF). These techniques are applied to phantom images of point, line, edge, and ring discontinuities. The model-dependent methods utilize multiparameter fits of a two-dimensional model function to the image data. Model predictions are compared with results obtained in a model-independent way by numerical transformation of the data. Results of resolution measurements of an Imatron C-100 CT scanner at UCSF and a second experimental scanner at the UCSF Physics Research Laboratory are presented.

Relative Carotid Blood Flow Measurements in Dogs by High-speed CT: A Preliminary Study

A high-speed computed tomography (CT) scanner was used for measuring flow in a phantom and in the common carotid arteries of six dogs. The general ability of the scanner to assess flow using contrast media boluses was tested with the phantom. The validated simple concept was then used in the animals. The carotid blood flow was varied with a distal occluder on one side and measured with electromagnetic flow probes in both vessels. The results are promising and demonstrate a good correlation between the high-speed CT findings and those measured with the flow probes.