Computed tomography of the heart: evaluation of anatomy and function.

Diseases of the heart and blood vessels represent one of the most challenging problems for advanced diagnostic imaging systems. Computed tomographic scanning is potentially an ideal cardiac imaging modality since it is a cross-sectional imaging method with very high resolution. Currently available computed tomographic scanners have exposure speeds of 1 to 5 seconds, which are inadequate for the majority of cardiovascular imaging applications. Nevertheless, a variety of limited computed tomographic scanning techniques have been successfully performed in selected patient subgroups. These methods require the administration of contrast medium injected or infused into a peripheral vein, combined with either dynamic computed tomographic scanning or some form of electrocardiographic gated computed tomography. The newer conventional computed tomographic scanners can display anatomic structures in the heart and great vessels with considerable fidelity and provide not only cross-sectional displays but also, by means of computer manipulation, any selected reconstructed images in oblique, coronal or sagittal projections. Feasibility studies indicate improved accuracy of computed tomographic measurements of cardiac chamber volumes. Physiologic measurements include estimation of shunt flows and cardiac output and analysis of myocardial wall thickening. The full potential of computed tomography should be reached once fast, multiple slice, computed tomographic scanners using scanning electron beam techniques become available. The prototype CVCT (cine computed tomographic C-100 scanner) designed at the University of California, San Francisco, is now undergoing evaluation. This instrument images up to eight contiguous slices at the rate of 16 to 24 images/s. The computed tomographic scanner specifically designed for cardiac imaging should extend the utility of computed tomography in the evaluation of cardiac diseases and the study of cardiovascular physiology.

In vivo assessment of left ventricular wall and chamber dynamics during transient myocardial ischemia using cine computed tomography.

Using a new computed tomographic (CT) scanner design that uses a rapidly moving focused electron beam, 50-ms CT scans were obtained at 2 axial levels simultaneously through the hearts of 6 dogs in order to analyze left ventricular (LV) wall thickness and cross-sectional chamber area after acute occlusion of the left anterior descending coronary artery (LAD). Ten or fifteen 50-ms CT scans (rate of 17 scans/s through the middle of the left ventricle were performed in 1 second (cine acquisition) during intravenous administration of contrast medium at rest, 60 seconds after acute occlusion of the LAD, and 60 seconds after release of the occlusion. The percent extent of systolic wall thickening of the potentially ischemic anterior segment was 37 +/- 15% (+/- standard deviation) in the control state and -5 +/- 6.5% during LAD occlusion (p less than 0.01). There was no significant difference in the percent change in LV luminal area from end-diastole to end-systole between the control state (50 +/- 19%) compared with LAD occlusion (47 +/- 21%). There were no significant differences in the extent of systolic wall thickening or LV luminal area between the control state and 60 seconds after release of occlusion. The alterations in regional myocardial function during acute ischemia are characterized by wall thinning during systole in the jeopardized segment and no significant change in global LV function. These features can be assessed by cine computed tomography during a solitary heart cycle.

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.

Bronchobiliary and bronchopleural fistulas.

In the course of treating approximately 2,000 patients with postoperative stricture of the bile duct, 16 bronchopleural and bronchobiliary fistulas were encountered. Three patients have been seen in the past year. This has prompted a review of our experience since it was previously recorded in 1955. Fistulous complications of obstructive biliary tract disease take three forms: (1) massive fulminating biliary empyema; (2) acute necrotizing bile bronchiolitis and pneumonia when pleural symphysis exists; and (3) a more indolent, chronic, recurring form of bronchobiliary communication. We have learned that transdiaphragmatic perforation occurs at a certain characteristic location in the diaphragm. An understanding of the pathological anatomy and pathogenesis has provided a specific and sequential mode of surgical treatment. When this has been adhered to strictly, cure has resulted.

Chronic interstitial pneumonitis with fibrosis after long-term therapy with nitrofurantoin.

Nitrofurantoin has been used widely as a urinary antiseptic. That it may cause pulmonary infiltration, and even fibrosis, has not been recognized universally. The literature contains 24 cases of interstitial pneumonitis with fibrosis. The results of treatment are summarized, and a new case is reported in detail.

A prototype high-purity germanium detector system with fast photon-counting circuitry for medical imaging.

A data-acquisition system designed for x-ray medical imaging utilizes a segmented high-purity germanium (HPGe) detector array with 2-mm wide and 6-mm thick elements. The detectors are contained within a liquid-nitrogen cryostat designed to minimize heat losses. The 50-ns pulse-shaping time of the preamplifier electronics is selected as the shortest time constant compatible with the 50-ns charge collection time of the detector. This provides the detection system with the fastest count-rate capabilities and immunity from microphonics, with moderate energy resolution performance. A theoretical analysis of the preamplifier electronics shows that its noise performance is limited primarily by its input capacitance, and is independent of detector leakage current up to approximately 100 nA. The system experimentally demonstrates count rates exceeding 1 million counts per second per element with an energy resolution of 7 keV for the 60-keV gamma ray photon from 241Am. The results demonstrate the performance of a data acquisition system utilizing HPGe detector systems which would be suitable for dual-energy imaging as well as systems offering simultaneous x-ray transmission and radionuclide emission imaging.

Determining cardiac velocity fields and intraventricular pressure distribution from a sequence of ultrafast CT cardiac images.

A method of computing the velocity field and pressure distribution from a sequence of ultrafast CT (UFCT) cardiac images is demonstrated. UFCT multi-slice cine imaging gives a series of tomographic slices covering the volume of the heart at a rate of 17 frames per second. The complete volume data set can be modeled using equations of continuum theory and through regularization, velocity vectors of both blood and tissue can be determined at each voxel in the volume. The authors present a technique to determine the pressure distribution throughout the volume of the left ventricle using the computed velocity field. A numerical algorithm is developed by discretizing the pressure Poisson equation (PPE), which Is based on the Navier-Stokes equation. The algorithm is evaluated using a mathematical phantom of known velocity and pressure-Couette flow. It is shown that the algorithm based on the PPE can reconstruct the pressure distribution using only the velocity data. Furthermore, the PPE is shown to be robust in the presence of noise. The velocity field and pressure distribution derived from a UFCT study of a patient are also presented.

Infected aortic grafts and aortic fistulas.

Infection in prosthetic grafts of the aorta and in the groin present different problems. Retroperitoneal sepsis must be treated by total removal of the graft. This is probably equally true for acutely infected grafts seen in enteric fistula. The surgical technique described can be performed in one stage. The principles of treatment for groin infections are the same as for infections associated with prosthetic grafts. The hazard is more to limb than to life, since the infection tends to point outward in the groin and thus be confined. The technique for dealing with groin infections, as presented, is straightforward.