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Temporal filtering methods were applied to iodine signal-to-noise ratio (SNR) restoration in intravenous hybrid subtraction digital subtraction angiography (DSA). For equal detected exposure rates hybrid subtraction had approximately 35% of the SNR of temporal subtraction. When matched filtering was applied to a DSA run, the filtered result had approximately two times higher SNR than the peak contrast image in the run. Thus, when matched filtering techniques were applied to the hybrid image sequence, the resultant SNR increased to about 70% of that of temporal subtraction. With an additional factor-of-two increase in exposure rate for the hybrid run, SNR parity with temporal subtraction could be achieved. This compared with a factor-of-nine increase in exposure that would be required if no filtering were performed. Experimental hybrid matched filter results, generated with intravenous canine DSA studies, supported the predictions in SNR performance.

Fifty-one arteriograms were obtained outside of the radiology department with portable digital subtraction angiographic equipment. Thirty-five studies were performed in the emergency room, 12 in the operating room, and four in the intensive care unit. There was a significant decrease in the time interval from arrival in the emergency room to arteriogram completion for examinations performed in the emergency room with portable equipment, compared with those performed in the radiology department. One of the 51 examinations yielded questionable results and was repeated with the conventional screen-film technique. Accurate angiographic diagnoses can be obtained by means of portable equipment in a variety of hospital locations.

A variation of temporal recursive filtering for intravenous and intra-arterial digital subtraction angiography (DSA) is described. It results in a dynamic tomographic DSA display that may improve intravenous DSA performance by removing the confusion introduced by vessel overlap and reducing the severity of motion artifacts. A conventional circular tomographic apparatus was modified by the addition of a 23-cm image intensifier-television chain and made to run continuously at one revolution each 1.5 seconds. The video output was processed by the recursive filter in a two-step process resulting in a dynamic tomographic display of arterial opacification. Theory and results of initial animal studies are presented.

Recent developments in digital subtraction angiographic imaging are discussed. The technical characteristics of several alternate subtraction methods are reviewed, including integrated remasking, matched filtering, recursive filtering, hybrid subtraction, and tomographic digital subtraction angiography (DSA). The properties that each exhibits are compared with conventional DSA imaging, and the major expected limitations and applications of each technique are discussed.

An inexpensive digital subtraction angiography (DSA) apparatus that can perform live subtraction, processed subtraction, and road mapping is described. The apparatus can be used in any standard x-ray room with fluoroscopic capability, with a simple connection to the existing TV chain. It is especially useful in therapeutic neuroangiography.

A new system for digital vascular subtraction imaging is presented. The image receptor consists of a rare-earth screen with light output optically focused onto the photocathode of a low-light-level image Isocon camera. This system represents a departure from the conventional use of the image intensifier for digital subtraction imaging. Our initial results suggest that this system could be competitive with traditional image intensifier systems and that it deserves clinical trial.

Initial clinical results using a digital fluoroscopic implementation of the combined time-energy ("hybrid") subtraction technique are described, with emphasis on carotid and renal imaging. Where patient motion artifacts are due to soft-tissue motion alone, hybrid subtraction can remove them. Due to the need for a finite separation time between high- and low-energy pairs, however, the present implementation of the hybrid technique is not completely immune to soft-tissue motion. The intrinsic signal-to-noise ratio of hybrid imaging is less than that of conventional temporal subtraction. However, since the low-energy temporal subtraction images are included in the hybrid data set, the diagnostic quality of the examination is not compromised.

A hybrid digital subtraction angiography technique and noise-reduction algorithm were used to evaluate the carotid bifurcation. Temporal, hybrid, and reduced-noise hybrid images were obtained in right and left anterior oblique projections, and both single- and multiple-frame images were created with each method. The resulting images were graded on a scale of 1 to 5 by three experienced neuroradiologists. Temporal images were preferred over hybrid images (average score = 3.2 and 2.4, respectively). The percentage of nondiagnostic examinations, as agreed upon by two readers, was higher for temporal alone than temporal + hybrid (4 and 1, respectively). In addition, also by agreement between two readers, temporal + hybrid images significantly increased the number of bifurcations seen in two views (87%) compared to temporal subtraction alone (64%).

A temporal high-pass filtration technique for digital subtraction angiocardiography was studied, using real-time digital studies performed simultaneously with routine cineangiocardiography (cine) for qualitative image comparison. The digital studies showed increased contrast and suppression of background anatomy and also enhanced detection of wall motion abnormalities when compared with cine. This digital technique is compatible with panning the image intensifier during an injection. The digital images are comparable with, and in some cases better than, cine images. Clinical efficacy of this digital technique is currently being evaluated. Real-time display, as well as potential reductions in radiation and contrast material doses, may make digital angiocardiography an attractive technique.