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The authors compared two techniques for performing runoff, contrast material-enhanced magnetic resonance (MR) angiography. Multiinjection time-resolved imaging of contrast kinetics (TRICKS) and single-injection bolus-chase MR angiographic examinations were performed in 10 volunteers and 10 patients. Image quality and venous overlay of the major blood vessels of the abdomen, thigh, and calf were evaluated. Significantly more (P <.05) vessels were depicted with diagnostic quality on multiinjection TRICKS than on single-injection bolus-chase MR angiographic images.

Purpose: To evaluate the feasibility of using magnetic resonance (MR) imaging to guide and monitor endovascular therapeutic procedures., Materials and Methods: Endovascular therapeutic procedures were performed with MR imaging guidance in eight dogs by using a 1.5-T MR unit with echo-planar imaging capabilities. Carotid arterial aneurysms were surgically created in four dogs. The ability to depict, track, and position catheters, guide wires, and Guglielmi detachable coils was assessed. Catheters were first positioned with fluoroscopic guidance. Tracking and depiction were achieved with MR imaging by using commercially available catheters filled with a gadopentetate dimeglumine solution and a fast, two-dimensional, time-resolved, variable-rate k-space sampling technique., Results: When either a catheter or the coaxial space between a catheter and a guide wire was filled with a solution of gadopentetate dimeglumine, catheter movement was always depicted. In the animals with aneurysms, it was possible to depict movement of a catheter into and out of the aneurysm. This was achieved by superimposing reconstructed images obtained during catheter movement onto a previously acquired MR angiogram ("road map"). Prototype Guglielmi detachable coils were successfully positioned and detached. Aneurysm obliteration was monitored with the acquisition of new road map images., Conclusion: The results demonstrate the feasibility of using MR imaging to guide endovascular therapeutic procedures.

Purpose: To compare the delineation of stenosis at the carotid artery bifurcation on three-dimensional (3D) magnetic resonance (MR) digital subtraction angiographic (DSA) images with that on two-dimensional (2D) and 3D time-of-flight (TOF) MR angiographic images., Materials and Methods: Twenty-six patients with 29 carotid artery bifurcations and symptoms of cerebral ischemia underwent 3D MR DSA. A time-resolved series was generated with 3D MR DSA after the bolus injection of gadodiamide. The resolution for a carotid artery examination was 0.4 x 0.4 x 1.0 mm, with volumes reconstructed at 4.5-second intervals. The 3D MR DSA images were compared with contemporaneously acquired unenhanced 2D and 3D TOF images. Two observers ranked the 2D and 3D TOF MR angiographic and 3D MR DSA images according to the following: (a) stenosis delineation, (b) internal carotid artery delineation, (c) intravascular signal intensity, and (d) diagnostic confidence., Results: The mean ranking for diagnostic confidence was 1.10 (1 = best technique, 3 = worst technique) for 3D MR DSA. Compared with the pooled 2D TOF and 3D TOF ranks, the 3D MR DSA rank was significantly better (P < .01). Similar levels of statistical significance were found for the other criteria., Conclusion: Three-dimensional MR DSA improves the delineation of carotid arterial stenosis by virtually eliminating saturation effects and reducing intravoxel dephasing. Surface morphology and nearly occluded vessels ("string sign") were easily identified. Confidence in identifying carotid arterial occlusions was also very high with this technique.

Purpose: To evaluate the imaging performance and patient tolerance of a blood-pool contrast agent (MS-325) for magnetic resonance (MR) angiography., Materials and Methods: Imaging of peripheral and carotid vessels was performed in seven healthy volunteers in a phase I clinical trial of the gadolinium chelate MS-325. Each volunteer received an intravenous injection of 0.05 mmol/kg MS-325 over 30 seconds. Dynamic (arterial phase) and steady-state (arterial-venous phase) three-dimensional gradient-echo MR angiograms were acquired during, immediately after, and approximately 50 minutes after injection. Images were ranked (1 [poor] to 5 [excellent]) for overall image quality, and signal-to-noise ratio (S/N) and contrast-to-noise ratio (C/N) were measured by using standard techniques., Results: All volunteers tolerated the procedure well. The MS-325-enhanced studies demonstrated intense vascular signal. Mean peripheral arterial C/N was 12.9 +/- 4.8 (standard deviation), 78.8 +/- 29.4, 46.1 +/- 10.9, and 41.9 +/- 14.1 for the two-dimensional (2D) time-of-flight (TOF) and the contrast material-enhanced dynamic, early steady-state, and late steady-state images, respectively. Image quality of steady-state postcontrast images was statistically significantly (P < .02) higher than that of 2D TOF images. Image quality of early and late postcontrast images was similar, but a small (10%) decrease in C/N was noted from early to late images., Conclusion: MS-325 provides excellent vascular and selective arterial enhancement during dynamic MR angiography. The long blood residence time also allows acquisition of steady-state images of the arteries and veins with excellent spatial resolution.

An electrocardiographically triggered two-dimensional phase-contrast (PC) magnetic resonance angiographic pulse sequence was developed in which velocity encoding (VENC) was varied throughout an acquisition in response to changes in blood velocity during the cardiac cycle. This was done to better capture signal in the peripheral vasculature, where pulsatile flow degrades images. After reconstruction, a matched filter addition technique was applied to the cardiac phase images to obtain a single high-quality static image. Images were obtained of six healthy volunteers--with and without varying VENC--and contrast-to-noise ratio (C/N) calculations were performed for the added images. Varying VENC significantly improved vascular signal from small and large vessels (P less than .02), but it was most helpful for small vessels, for which the C/N increased by as much as 260% (average increase, 149%). These preliminary findings suggest that variable VENC can enhance the signal from the small and large peripheral blood vessels in cardiac-gated PC acquisitions.

Recent reports have emphasized the potential for dual-energy computed radiographic applications. An improved method for single-exposure material-selective imaging with a photostimulable phosphor computed radiography system was investigated. The essential elements of the technique are (a) prefiltration with gadolinium, which divides the incident broad-beam x-ray spectrum into low-energy and high-energy peaks; (b) a cassette consisting of four photostimulable phosphor plates that record images of increasing mean energies, with a computed energy separation of 23 keV from the front to the rear plate; (c) spatially dependent scatter and beam-hardening corrections; and (d) a noise-reduction algorithm based on noise correlations between bone-selective and soft-tissue-selective dual-energy images. These elements result in improved material cancellation and signal-to-noise ratio throughout the image.

The excellent linearity of digital image storage and retrieval permits hybrid analog-digital subtraction to extend the spatial resolution of two previously developed algorithms which employed entirely digital apparatus. A low resolution, time-integrated preinjection digital mask image is reconverted to analog form and subtracted from live analog video images of iodine administered by peripheral intravenous injection to produce a high resolution display of the cardiovascular system with contrast ten times greater than conventional fluoroscopy. Preliminary studies in dogs are compared with images obtained with our digital subtraction algorithms.

Digital video subtraction angiography (DVSA) has been employed to study a variety of peripheral vascular problems, using equipment developed at the University of Wisconsin. The technique is relatively simple and safe and has good patient acceptance. Experience indicates that in selected patients it is a satisfactory alternative to standard arteriography for screening and for definitive evaluation and on occasion may yield information not obtainable with conventional methods. It can aid in the performance of transluminal angioplasty and is suitable for serial evaluation of atherosclerotic vessels and bypass grafts.

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.

Left ventricular ejection fractions were determined following eight intravenous injections in three dogs using area/length and digital videodensitometric techniques. Ejection fractions were measured by both techniques for all beats during left ventricular opacification. Even after noniodinated background corrections, tissue iodine accumulation produced large errors in measured iodine content late in the contrast material curve. By using a model for tissue iodine accumulation, an algorithm was developed that appears to reduce these errors. The measured ejection fraction for ten beats following the peak of the contrast material curve declined an average of 1.8% following correction, compared with 14% prior to correction. Following correction for tissue iodine accumulation, correlation between area/length and video-densitometric ejection fractions was 0.94. By correcting for tissue iodine accumulation, much more of the contrast material curve provides usable data for estimating ejection fractions.

The feasibility of producing patient-specific beam attenuators for chest radiography has been investigated using an anthropomorphic phantom and a human volunteer. A low-dose test exposure is digitized, processed, and used to print a small cerium filter, which is placed in the x-ray beam near the collimator. The final radiograph is recorded on film. The technique results in relatively uniform film exposure, so that structures in all regions of the chest are simultaneously displayed with optimal film contrast. The equalized exposure improves image quality in the normally underpenetrated regions and reduces the role of cross-scatter from the lungs. The image is analogous to optical or computer-processed unsharp masking techniques, but the processing is accomplished in the x-ray beam and results in an improved exposure distribution, giving advantages that cannot be achieved with image processing techniques alone.

K-edge subtraction images have been produced using a digital video image processor. Images formed by three filtered x-ray beams are detected by an image intensifier-Plumbicon system, digitilized, and combined in real time to produce bone- and tissue-free K-edge subtraction images of iodinated structures. Preliminary studies of rhesus monkey cranial, spinal, and abdominal structures are compared with those of conventional radiography.

The logarithmic amplification of video signals and the availability of data in digital form make digital subtraction videoangiography a suitable tool for videodensitometric estimation of physiological quantities. A system for this purpose was implemented with a digital video image processor. However, it was found that the radiation scattering and veiling glare present in the image-intensified video must be removed to make meaningful quantitations. An algorithm to make such a correction was developed and is presented. With this correction, the videodensitometry system was calibrated with phantoms and used to measure the left ventricular ejection fraction of a canine heart.

Preliminary results obtained with a new computerized fluoroscopic apparatus in examination of the extracranial carotid arteries are described. All patients had clinical signs of symptoms of extracranial occlusive vascular disease. In most cases, image quality was sufficient to display patency of the internal carotid arteries, with excellent correlation between intravenous and conventional angiography. While the new technique is not totally noninvasive, it does eliminate many of the risks and costs of conventional arteriography.