Fred H. Burbank

Determinants of Contrast Enhancement for Intravenous Digital Subtraction Angiography

Mask mode intravenous digital subtraction angiography (IV-DSA) image quality is directly dependent on the arterial time-concentration curve peak and width produced by contrast media. Curves with high peak iodine concentration produce excellent difference images. Curves that are narrow appear and disappear quickly and minimize movement artifacts. Using a noninvasive x-ray technique for quantitative measurement of contrast media time-concentration curve parameters and cardiac output, three experimental data bases were analyzed. From the analyses, equations defining curve peak and width were derived and validated. Width is proportional to central blood volume and inversely proportional to cardiac output. Peak is proportional to the quantity of contrast media injected and inversely proportional to central blood volume. Hypertonic contrast media increases central blood volume and lowers curve peak. Optimal contrast media for IV-DSA is low in concentration and high in volume. In addition, low concentration contrast media may be more comfortable for the patient causing fewer motion artifacts.

An Experimental Evaluation of Central vs. Peripheral Injection for Intravenous Digital Subtraction Angiography (IV-DSA)

At a given radiation dosage and field of view, five variables are under meaningful control for intravenous digital subtraction angiography (IV-DSA): concentration and quantity of contrast media injected, volume of injectate, rate of injection, and site of injection. Some controversy exists regarding the selection of a central vs. a peripheral injection site for IV-DSA. This study determined the influence of the site of injection on the peak and width of the arterial time-concentration curve produced by contrast media. Using a noninvasive, in vivo, quantitative x-ray measurement method, 36 separate injections (10 ml of ioxaglate at 8 ml/sec) were administered into the cephalic vein, subclavian vein, and main pulmonary artery in dogs. Injection sites were varied using a Latin-square experimental design. Cardiac output, central blood volume and the peak and width of the contrast media time-concentration curves were measured. The average peak enhancement was greatest for the pulmonary artery injection site. Normalizing peak and width values to make the pulmonary artery values 100%, the average peak values for injections into the subclavian vein and cephalic vein were 93% and 56%, and the average widths were 141% and 163%, respectively. These data support the use of a more central injection site for optimizing IV-DSA examinations.

Effect of volume and rate of contrast medium injection on intravenous digital subtraction angiographic contrast medium curves

The image quality of temporal (mask mode) intravenous digital subtraction angiography is directly dependent on the shape of arterial time-concentration curves produced by the intravenous injection of contrast medium. Curves that are narrow and tall minimize motion artifact (misregistration) and maximize contrast enhancement (pre- and postcontrast differences). To determine the effects of rate and volume of injection of contrast medium on intravenous digital subtraction angiographic curves, ioxaglate (Hexabrix), a monoacidic ionic dimer, was injected into large mongrel dogs. Quantitative measurements of opacification were made over time in the femoral arteries using a modified General Electric CT/T scanner. Peak opacification was directly proportional to the volume of contrast medium injected. Curve width was not affected by increasing volume of injection. At rates below a critical point, slower injection rates produced progressively shorter and wider arterial time-concentration curves. Above that critical point, increasing the rate of injection did not affect either curve width or curve peak.

A QUANTITATIVE IN VIVO COMPARISON OF SIX CONTRAST AGENTS BY DIGITAL SUBTRACTION ANGIOGRAPHY

Burbank FH, Brody WR, Hall A, Keyes G. A quantitative in vivo comparison of six contrast agents by digital subtraction angiography. Invest Radio! 1982; 17:610–616. Digital subtraction angiography (DSA) technology can now visualize many significant arterial structures from intravenous injections of contrast media. Image quality of these DSA studies is related to contrast agent enhancement. This study compares contrast agents of differing iodine concentration, viscosity, and osmolarity. A technique is described that utilizes a scanned projection digital radiographic system to compare quantitatively degrees of intra-arterial opacification after the administration of six intravenous contrast agents: iothalamate (at four different concentrations and in combinations with two different cations), diatrizoate, and ioxaglate. The quantitative arterial enhancement was compared in dogs utilizing an extra- period latin-square multiple change-over clinical trial design. The contrast agents span a range of organically bound iodine from 282 mg I/ml to 480 mg I/ml. When rate and volume of contrast agent injected are held constant, intra-arterial opacification is directly a function of the iodine concentration (mg I/ml) of the agent injected, while osmolarity and viscosity have no effect on opacification. These studies support the use of agents with high iodine concentration for maximum vascular visualization.

Contrast media tonicity. Part I. Effects upon IV-DSA time-concentration curve peak and width: experimental studies.

Prior to the formation of an intravenous digital subtraction angiography (IV-DSA) image, contrast medium passes through the lesser circulation and is diluted by the blood volume of the heart and lungs. If the contrast medium alone influences central blood volume or cardiac output, the shape of the resultant time-concentration curve may be degraded. To the extent that contrast medium tonicity reduces curve peak or increases width, image quality for mask mode IV-DSA will suffer. To quantify the effect of contrast medium tonicity upon curve shape, contrast medium (1) at increasing iodine concentration and increasing osmolality and (2) at constant iodine concentration and increasing osmolality was injected into the right atria of mongrel dogs. In both experiments, increasing osmolality was associated with an increase in central blood volume (CBV) and cardiac output. With an increase in CBV, curve peak fell. With an increase in both CBV and cardiac output, curve width was not influenced by increasing osmolality. The effect of osmolality upon CBV was highly variable; in these experiments CBV was influenced more by subject-to-subject variability. However, on the average, higher tonicity contrast media produced curves with lower peaks. These studies suggest that isotonic contrast medium does not increase CBV and that isotonic contrast medium is preferable to hypertonic contrast medium for IV-DSA image formation.

Digital radiographic evaluation of the bile ducts.

This study compares digital radiographic images of the bile ducts in dogs with images obtained using routine radiography. The dogs were infused with iodipamide (2 ml/minute for 30 minutes), and the bile ducts were imaged at 60 minutes using plain radiograph and five digital techniques: (1) dual-energy, (2) DSA-hybrid prepixel shift, (3) DSA-hybrid postpixel shift, (4) a dual-energy film system--Digirad, and (5) scan projection radiography using hybrid subtraction. Six radiologists who were not familiar with digital radiography evaluated the six different studies. The images were presented in a randomized order and each image was evaluated on a five-point scale. There was no difference between the plain radiographs and the dual-energy images. Both of these studies were rated significantly better (P less than .001) than the other four digital images. These results suggest that digital radiography during direct cholangiography may be easily accomplished using a 10% to 15% iodine solution.