(Radiographics. 2000;20:121-133.)
© RSNA, 2000
Optimized Diagnostic Angiography in High-Risk Patients with Severe Peripheral Vascular Disease1
Julia Gates, MD and
George Gordon Hartnell, FRCR
1 From the Department of Radiology, Beth Israel Deaconess Medical Center, Boston, Mass. Presented as a scientific exhibit at the 1998 RSNA scientific assembly. Received March 1, 1999; revision requested April 14 and received May 27; accepted May 28. Address reprint requests to G.G.H., CVDL, Blalock 545, Department of Radiology, Johns Hopkins Hospital, 600 N Wolfe St, Baltimore, MD 21287.
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Abstract
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Conventional arteriography remains the usual method for preoperative assessment of severe peripheral vascular disease (PVD). Unfortunately, many peripheral arteriograms are still performed with a suboptimal technique, which can cause significant diagnostic errors in patients with severe PVD. A suboptimal technique may be due to poor collimation (causing incorrect exposure and incorrect gray scale), excessive patient-film distance (magnification unsharpness), inadequate volume or density of contrast material, poor contrast resolution (screen-film arteriography), nonselective injection, patient movement, and pressure from restraints or incorrect patient position (failure to profile lesions, pseudo-occlusion from external pressure or plantar flexion). The technique of selective digital subtraction arteriography (DSA) allows one to avoid these errors. The superior contrast resolution of DSA allows use of lower concentrations of contrast material. Selective injection into the external iliac artery allows proper positioning and improves image quality. Demonstration of distal vessels is best achieved by using biplane arteriography. For patients with severe resting ischemia, especially those with diabetes, high-quality selective DSA is essential to ensure that all distal vessels suitable for distal bypass grafting are identified. When properly performed, selective DSA remains the investigation of choice for reliably demonstrating arterial anatomy in high-risk patients with severe PVD.
Index Terms: Angiography, preoperative, 92.122 • Arteries, extremities, 92.72 • Arteries, stenosis or obstruction, 92.72
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Introduction
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Conventional (ie, contrast material) arteriography has long been regarded as the standard technique for assessing arterial anatomy in patients with peripheral vascular disease (PVD). However, there is substantial evidence that important diagnostic errors can occur with conventional arteriography as usually practiced (1–4). Such errors occur particularly in patients with severe, chronic PVD manifesting as resting ischemia. Patients with chronic resting ischemia manifesting as ulceration and gangrene—especially those with diabetes—usually have severe infrapopliteal disease in addition to iliac or femoral artery disease (5). Usually, the best possibility for relief of ischemia of this severity is a distal bypass graft (DBPG), which requires reliable demonstration of patent distal segments of calf or foot arteries (6).
There have been great improvements in the assessment of PVD with ultrasonography (US), computed tomographic angiography, and magnetic resonance (MR) angiography. These techniques have all been compared with conventional angiography, and claims have been made about their relative accuracies. In all reported comparative studies of assessment of severe PVD, to our knowledge, there have been limitations in the quality of the conventional angiography (7–9). Similar limitations are present and illustrated in specific descriptions of conventional angiography for severe PVD (1,10,11). Conventional angiography is still recommended as the best preoperative method of defining arterial anatomy (4). On the basis of our experience, selective digital subtraction arteriography (DSA) remains the standard of reference for demonstrating the full extent of severe PVD in high-risk patients with resting ischemia and tissue loss (3).
The role of arteriography in patients with PVD is to accurately demonstrate the involvement or patency of all arterial segments from the aorta to the feet. These patients usually have obstructive disease at multiple levels, and safe demonstration of all anatomic segments, irrespective of proximal obstruction, is essential (2,6). Reliable identification of patent distal vessels is required for limb salvage with a DBPG; such identification requires the highest-quality arteriography, which is often not achieved (3,12). In 31 patients referred to our hospital for consideration for a DBPG for critical lower limb ischemia, 26 (84%) of the arteriograms from other institutions were thought by the vascular surgeon to provide inadequate information about the distal arteries. All patients had severe peripheral ischemia that would have necessitated amputation if a DBPG could not be placed. In 21 of 30 limbs evaluated, selective DSA demonstrated a suitable distal artery that allowed successful DBPG placement (3).
On the basis of this experience, we illustrate errors in conventional arteriography for severe PVD (Table 1), suggest how to avoid making similar errors, and describe how to achieve optimal imaging safely. Patient preparation, arterial access, and the technique of selective DSA are described, followed by a discussion of nonselective versus selective injection, radiographic technique, patient positioning, peripheral vasodilators, and procedure safety. Many patients with severe PVD have multiple risk factors for complications of conventional arteriography. In our practice, among patients evaluated for severe PVD, over two-thirds had diabetes, over one-half had heart disease, and at least one-sixth had renal disease. Nevertheless, with use of a careful technique and preparation, selective DSA can be performed with a low complication rate (Table 2).
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Patient Preparation
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Preparation for conventional arteriography is similar for patients with and patients without diabetes. There is a higher prevalence of cardiac disease and renal disease in patients with diabetes, but all patients with severe PVD are at increased risk. The severity of cardiac and renal disease should be evaluated before conventional arteriography. The risk of contrast material–induced renal insufficiency associated with conventional arteriography is low (2% or less depending on the definition of renal insufficiency) but is increased by diabetes (to about 16% in nonazotemic patients) and by renal insufficiency (13). In patients with diabetes and azotemia, the reported risk of renal failure may exceed 30% (13).
Fortunately, most episodes of renal failure are brief and of no clinical significance. A minority of such episodes may affect patient care, and a few lead to dialysis. The risk of contrast material–induced renal insufficiency is reduced by good preprocedure hydration, such as intravenous administration of 0.9% saline solution or 5% dextrose and 0.45% saline solution at 100 mL/h or more for 12 hours (14). Patients with a significant history of cardiac disease, who are at risk for heart failure, should receive a smaller volume (eg, 5% dextrose and 0.45% saline solution or 5% dextrose at 60 mL/h for 12 hours). There is no good
evidence that pretreatment with furosemide, felodipine, or mannitol is beneficial. In some studies, these agents had a deleterious effect when compared with intravenous hydration alone (14,15).
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Arterial Access
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Femoral arteriograms are obtained by using a retrograde femoral approach unless a brachial approach is indicated. Unilateral lower extremity arteriography tends to be performed from an ipsilateral approach; bilateral lower extremity arteriography is performed by advancing the catheter (eg, Sos Omni Flush [AngioDynamics, Queensbury, NY], Cobra-2) over the aortic bifurcation to study the contralateral limb before pulling the catheter back for ipsilateral imaging.
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Technique of Selective DSA
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The best arteriographic study for severe PVD with resting ischemia, which often complicates diabetes, involves DSA instead of conventional screen-film arteriography, with which many patent arterial segments may be missed (1,16,17). Multilevel DSA allows optimum positioning, timing, and collimation at each level. Current dedicated DSA systems with a 1,024 x 1,024 imaging matrix and a 12–16-inch (30–40-cm) image intensifier have a spatial resolution only slightly worse than that of current screen-film systems (typically 3 line pairs per millimeter for DSA versus 5–6 line pairs per millimeter for screen-film technology). This difference is of little clinical significance and is more than compensated for by the greater contrast resolution of DSA and the subtraction of obscuring bone opacity. The ability of selective DSA to demonstrate patent vessels beyond an occlusion is superior to that of screen-film arteriography or nonselective DSA.
Biplane angiography of distal calf vessels allows confident identification of isolated distal arterial segments, provided frontal imaging is performed perpendicular to the interosseous membrane (Table 3). Confident identification of such segments is not always possible when single-plane imaging is used, as demonstrated in some comparative studies (9,18,19). Unsuccessful or incomplete examinations and examinations with indeterminate results are infrequent with selective DSA relative to other techniques, with which 10%–20% of segments may be uninterpretable or assessed incorrectly (9,18). Biplane angiography is also recommended to better profile lesions, which may be eccentric and over- or underestimated with single-plane angiography. Biplane imaging produces mutually orthogonal images (frontal and lateral views), which are obtained with separate injections and repositioning of the patient and the tube. Every attempt should be made to obtain two views of the lower leg and foot. If only one view can be obtained, a lateral image tends to be more useful. Selective external iliac artery injections for DSA of the lower extremities should be standard unless it is dangerous or impossible to advance the catheter into the external iliac artery (for brachial artery or contralateral femoral artery approaches).
Selective DSA is monitored during image acquisition to ensure appropriate timing, unlike screen-film arteriography. The superior contrast resolution of DSA allows use of lower concentrations of contrast material (typically 30% versus 76% for screen-film arteriography). A lower contrast material concentration is more comfortable for the patient, thereby reducing movement artifacts, even when conventional high-osmolality contrast material is used. With a standard technique (Table 3), aortography and unilateral selective DSA with biplane imaging of the foot and calf arteries require a mean volume of 175 mL of 30% contrast material, which is equivalent to 69 mL of full-strength (76%) contrast material. Aortography and bilateral selective DSA require a mean contrast material volume of 242 mL, which is equivalent to 96 mL of 76% contrast material (3).
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Nonselective versus Selective Injection
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Conventional peripheral arteriography is often performed with simultaneous imaging of both lower limbs after contrast material injection into the aorta (Figs 1, 2). Screen-film arteriography may be adequate for patients with intermittent claudication due to supragenicular disease but is less suitable for patients with more severe distal PVD (Fig 3) and is frequently inaccurate in these patients (1–3). Also, it is impossible when imaging both lower limbs to achieve optimum positioning of the distal lower limbs, which is particularly important for demonstrating foot arteries (Figs 1–3).
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Figure 1a. (a) Composite image acquired with a DSA stepping technique shows bilateral popliteal artery aneurysms (arrows). An aortic injection was used with simultaneous imaging of both lower limbs. Although there is a suggestion of calf vessels in both lower limbs, it is unclear whether these would be suitable for a DBPG. (b) DSA image (nonstepping) acquired with contrast material injection into the lower aorta shows faint opacification of calf arteries but no vessels in either foot. Note the difficulty of obtaining uniform exposure over the whole image even with use of edge filters (*) and the poor anatomic positioning. (c) Selective DSA image (contrast material injection into the right external iliac artery) shows proper true lateral positioning and optimum exposure, as well as a bifid right posterior tibial artery (arrowheads) suitable for a DBPG.
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Figure 1b. (a) Composite image acquired with a DSA stepping technique shows bilateral popliteal artery aneurysms (arrows). An aortic injection was used with simultaneous imaging of both lower limbs. Although there is a suggestion of calf vessels in both lower limbs, it is unclear whether these would be suitable for a DBPG. (b) DSA image (nonstepping) acquired with contrast material injection into the lower aorta shows faint opacification of calf arteries but no vessels in either foot. Note the difficulty of obtaining uniform exposure over the whole image even with use of edge filters (*) and the poor anatomic positioning. (c) Selective DSA image (contrast material injection into the right external iliac artery) shows proper true lateral positioning and optimum exposure, as well as a bifid right posterior tibial artery (arrowheads) suitable for a DBPG.
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Figure 1c. (a) Composite image acquired with a DSA stepping technique shows bilateral popliteal artery aneurysms (arrows). An aortic injection was used with simultaneous imaging of both lower limbs. Although there is a suggestion of calf vessels in both lower limbs, it is unclear whether these would be suitable for a DBPG. (b) DSA image (nonstepping) acquired with contrast material injection into the lower aorta shows faint opacification of calf arteries but no vessels in either foot. Note the difficulty of obtaining uniform exposure over the whole image even with use of edge filters (*) and the poor anatomic positioning. (c) Selective DSA image (contrast material injection into the right external iliac artery) shows proper true lateral positioning and optimum exposure, as well as a bifid right posterior tibial artery (arrowheads) suitable for a DBPG.
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Figure 2a. (a) DSA image obtained after nonselective injection shows both feet with arterial detail obscured by movement artifact (note the bone edges revealed by movement [arrowheads]). This artifact occurred despite use of restraining straps, which may occlude an underlying vessel. Arrow = site of compression by strapping. (b) Selective DSA image obtained with true lateral positioning shows a distal left peroneal artery (solid arrow) and a narrowed anterior tibial artery (open arrow), which were not seen with the nonselective injection (a).
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Figure 2b. (a) DSA image obtained after nonselective injection shows both feet with arterial detail obscured by movement artifact (note the bone edges revealed by movement [arrowheads]). This artifact occurred despite use of restraining straps, which may occlude an underlying vessel. Arrow = site of compression by strapping. (b) Selective DSA image obtained with true lateral positioning shows a distal left peroneal artery (solid arrow) and a narrowed anterior tibial artery (open arrow), which were not seen with the nonselective injection (a).
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Figure 3a. (a) Conventional screen-film arteriogram (lateral view) obtained with the foot in plantar flexion and an overexposed technique shows some proximal vessels but no foot arteries. Correct exposure over all the areas of interest is impossible due to angulation of the ankle, but the exposure could be improved. (b) Unsubtracted digital arteriogram (lateral view) obtained with the foot in dorsiflexion shows how the ability to position edge filters (*) and optimize exposure allows better demonstration of foot vessels. Arrow = dorsal artery of foot. (c) Selective DSA image (from the same acquisition as in b) shows the dorsal artery of the foot and distal vessels, which were previously obscured by bone opacity.
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Figure 3b. (a) Conventional screen-film arteriogram (lateral view) obtained with the foot in plantar flexion and an overexposed technique shows some proximal vessels but no foot arteries. Correct exposure over all the areas of interest is impossible due to angulation of the ankle, but the exposure could be improved. (b) Unsubtracted digital arteriogram (lateral view) obtained with the foot in dorsiflexion shows how the ability to position edge filters (*) and optimize exposure allows better demonstration of foot vessels. Arrow = dorsal artery of foot. (c) Selective DSA image (from the same acquisition as in b) shows the dorsal artery of the foot and distal vessels, which were previously obscured by bone opacity.
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Figure 3c. (a) Conventional screen-film arteriogram (lateral view) obtained with the foot in plantar flexion and an overexposed technique shows some proximal vessels but no foot arteries. Correct exposure over all the areas of interest is impossible due to angulation of the ankle, but the exposure could be improved. (b) Unsubtracted digital arteriogram (lateral view) obtained with the foot in dorsiflexion shows how the ability to position edge filters (*) and optimize exposure allows better demonstration of foot vessels. Arrow = dorsal artery of foot. (c) Selective DSA image (from the same acquisition as in b) shows the dorsal artery of the foot and distal vessels, which were previously obscured by bone opacity.
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Selective injection into the ipsilateral external iliac artery improves image quality for infrainguinal arteriography (20). Imaging one limb at a time allows more effective immobilization (Fig 2), proper positioning of edge filters (Fig 3), and collimation to optimize exposure (Fig 4). Selective contrast material injection into the external iliac artery allows proper positioning for true lateral (Figs 1–3) and anteroposterior (Fig 4) imaging. Such imaging allows precise identification of isolated distal arterial segments that may be suitable for a DBPG.
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Figure 4a. (a) Selective DSA image of the right foot shows the effects of inadequate collimation: compression of the gray scale and reduced image contrast. (b) Equivalent mask image from a shows a range of opacity from air (*) to bone. (c) Selective DSA image obtained with closer collimation but identical contrast material volume, elapsed time, and windowing as in a shows foot vessels more clearly due to better image contrast. (d) Equivalent mask image from c shows a lesser range of opacity from soft tissue to bone, with air opacity now excluded. As a result, the tarsal bone edges are easier to see.
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Figure 4b. (a) Selective DSA image of the right foot shows the effects of inadequate collimation: compression of the gray scale and reduced image contrast. (b) Equivalent mask image from a shows a range of opacity from air (*) to bone. (c) Selective DSA image obtained with closer collimation but identical contrast material volume, elapsed time, and windowing as in a shows foot vessels more clearly due to better image contrast. (d) Equivalent mask image from c shows a lesser range of opacity from soft tissue to bone, with air opacity now excluded. As a result, the tarsal bone edges are easier to see.
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Figure 4c. (a) Selective DSA image of the right foot shows the effects of inadequate collimation: compression of the gray scale and reduced image contrast. (b) Equivalent mask image from a shows a range of opacity from air (*) to bone. (c) Selective DSA image obtained with closer collimation but identical contrast material volume, elapsed time, and windowing as in a shows foot vessels more clearly due to better image contrast. (d) Equivalent mask image from c shows a lesser range of opacity from soft tissue to bone, with air opacity now excluded. As a result, the tarsal bone edges are easier to see.
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Figure 4d. (a) Selective DSA image of the right foot shows the effects of inadequate collimation: compression of the gray scale and reduced image contrast. (b) Equivalent mask image from a shows a range of opacity from air (*) to bone. (c) Selective DSA image obtained with closer collimation but identical contrast material volume, elapsed time, and windowing as in a shows foot vessels more clearly due to better image contrast. (d) Equivalent mask image from c shows a lesser range of opacity from soft tissue to bone, with air opacity now excluded. As a result, the tarsal bone edges are easier to see.
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Nonselective digital subtraction aortography and runoff evaluation performed with a stepping table technique has recently been promoted and is available on most new DSA systems. Although this technique rapidly enables good demonstration of proximal arterial anatomy, demonstration of vessels below the knees is poor due to dilution of contrast material and limited spatial resolution. In addition, involuntary patient movement in the time between acquisition of the mask and contrast material–enhanced images often causes severe subtraction artifact with further obscuration of the distal vessels (Figs 1, 5).
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Figure 5. Composite image produced with stepping DSA (aortic injection) in a patient with multiple superficial femoral and popliteal artery stenoses clearly shows the proximal arteries. However, artifact due to movement between acquisition of the mask and contrast-enhanced images obscures the infrapopliteal arteries. Rotational movement is greatest in the lower part of the limb, and the interval between acquisition of the mask and contrast-enhanced images is also greatest for infrapopliteal imaging. It is impossible to optimally position both feet with this technique.
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Radiographic Technique
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Improper Radiographic Settings
Correct setting of radiographic parameters is essential to achieve good-quality arteriography, even when DSA is used. Use of an inadequate dose rate produces noise with individual scintillations visible (Fig 6). Use of too high a dose may also reduce image contrast so that even with DSA it is impossible to see any vessels (Fig 7), even with good collimation and selective injection.
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Figure 6a. (a) Selective DSA image (lateral view) acquired with older equipment at another institution and with poor collimation shows image noise, which obscures some finer vessels and suggests a focal occlusion of the left dorsal foot artery (arrow). (b) Equivalent unsubtracted image shows the extent to which air is included in the field of view. The inclusion of air causes gray-scale compression and flare, leading to poor image contrast compounded by use of older equipment. The patient positioning and contrast material injection were good. (c) Unsubtracted digital arteriogram (lateral view) obtained with the foot more dorsiflexed shows the ability to position edge filters (*) and achieve optimum exposure with newer equipment, producing a clearer, less noisy image. (d) Selective DSA image (from the same acquisition as in c) shows fine vessel detail previously obscured by noise and bone opacity and reveals that the dorsal artery occlusion is actually a stenosis (arrow).
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Figure 6b. (a) Selective DSA image (lateral view) acquired with older equipment at another institution and with poor collimation shows image noise, which obscures some finer vessels and suggests a focal occlusion of the left dorsal foot artery (arrow). (b) Equivalent unsubtracted image shows the extent to which air is included in the field of view. The inclusion of air causes gray-scale compression and flare, leading to poor image contrast compounded by use of older equipment. The patient positioning and contrast material injection were good. (c) Unsubtracted digital arteriogram (lateral view) obtained with the foot more dorsiflexed shows the ability to position edge filters (*) and achieve optimum exposure with newer equipment, producing a clearer, less noisy image. (d) Selective DSA image (from the same acquisition as in c) shows fine vessel detail previously obscured by noise and bone opacity and reveals that the dorsal artery occlusion is actually a stenosis (arrow).
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Figure 6c. (a) Selective DSA image (lateral view) acquired with older equipment at another institution and with poor collimation shows image noise, which obscures some finer vessels and suggests a focal occlusion of the left dorsal foot artery (arrow). (b) Equivalent unsubtracted image shows the extent to which air is included in the field of view. The inclusion of air causes gray-scale compression and flare, leading to poor image contrast compounded by use of older equipment. The patient positioning and contrast material injection were good. (c) Unsubtracted digital arteriogram (lateral view) obtained with the foot more dorsiflexed shows the ability to position edge filters (*) and achieve optimum exposure with newer equipment, producing a clearer, less noisy image. (d) Selective DSA image (from the same acquisition as in c) shows fine vessel detail previously obscured by noise and bone opacity and reveals that the dorsal artery occlusion is actually a stenosis (arrow).
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Figure 6d. (a) Selective DSA image (lateral view) acquired with older equipment at another institution and with poor collimation shows image noise, which obscures some finer vessels and suggests a focal occlusion of the left dorsal foot artery (arrow). (b) Equivalent unsubtracted image shows the extent to which air is included in the field of view. The inclusion of air causes gray-scale compression and flare, leading to poor image contrast compounded by use of older equipment. The patient positioning and contrast material injection were good. (c) Unsubtracted digital arteriogram (lateral view) obtained with the foot more dorsiflexed shows the ability to position edge filters (*) and achieve optimum exposure with newer equipment, producing a clearer, less noisy image. (d) Selective DSA image (from the same acquisition as in c) shows fine vessel detail previously obscured by noise and bone opacity and reveals that the dorsal artery occlusion is actually a stenosis (arrow).
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Figure 7a. (a) Selective DSA image (lateral view) of the right foot shows the effect of a high-dose technique. Vessels are visible only where overlying bone or a sufficient thickness of soft tissue has reduced the exposure (arrowheads) to within the gray-scale range. Vessels outside this area have become invisible (burnout) (arrows). (b) Equivalent unsubtracted digital image shows the position of the bones; the thicker soft tissues; and the bright, overexposed area causing burnout.
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Figure 7b. (a) Selective DSA image (lateral view) of the right foot shows the effect of a high-dose technique. Vessels are visible only where overlying bone or a sufficient thickness of soft tissue has reduced the exposure (arrowheads) to within the gray-scale range. Vessels outside this area have become invisible (burnout) (arrows). (b) Equivalent unsubtracted digital image shows the position of the bones; the thicker soft tissues; and the bright, overexposed area causing burnout.
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Collimation
Inadequate collimation causes overexposure of parts of the image, leading to gray-scale compression (Fig 4). A compressed gray scale makes it difficult to display diagnostic images without excessive postprocessing contrast enhancement (which emphasizes noise within the image). Gray-scale compression increases the visibility of image noise, which can obscure lesions and the residual lumen in severe stenoses (Fig 8). In addition, good collimation is required, with correct positioning, to minimize the effect of overexposure in areas of low attenuation, which causes flare or burnout. When burnout occurs, the exposure lies outside the range of the gray scale, thus making it impossible to see anything in the "burnt out" area, irrespective of the amount of contrast material injected or electronic postprocessing (Fig 6).
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Figure 8a. (a) Unsubtracted digital image (posteroanterior view) of the left leg shows a wide range of opacities. Exclusive of the knee replacement, the range of opacities includes air (*) and dense cortical bone, thus leading to gray-scale compression. A low-dose technique also contributed to the noisy image quality. (b) Selective DSA image (posteroanterior view) shows a noisy image due to gray-scale compression (a result of poor collimation) and a low-dose technique. The noise impairs demonstration of a complex stenosis at the popliteal trifurcation (arrow). (c) Selective DSA image (oblique view to project the popliteal artery behind the knee replacement) obtained with a higher-dose technique and better collimation shows the complex stenosis at the popliteal trifurcation (arrow) more clearly. There is also a mid-popliteal artery stenosis (obscured by the knee replacement in a and b).
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Figure 8b. (a) Unsubtracted digital image (posteroanterior view) of the left leg shows a wide range of opacities. Exclusive of the knee replacement, the range of opacities includes air (*) and dense cortical bone, thus leading to gray-scale compression. A low-dose technique also contributed to the noisy image quality. (b) Selective DSA image (posteroanterior view) shows a noisy image due to gray-scale compression (a result of poor collimation) and a low-dose technique. The noise impairs demonstration of a complex stenosis at the popliteal trifurcation (arrow). (c) Selective DSA image (oblique view to project the popliteal artery behind the knee replacement) obtained with a higher-dose technique and better collimation shows the complex stenosis at the popliteal trifurcation (arrow) more clearly. There is also a mid-popliteal artery stenosis (obscured by the knee replacement in a and b).
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Figure 8c. (a) Unsubtracted digital image (posteroanterior view) of the left leg shows a wide range of opacities. Exclusive of the knee replacement, the range of opacities includes air (*) and dense cortical bone, thus leading to gray-scale compression. A low-dose technique also contributed to the noisy image quality. (b) Selective DSA image (posteroanterior view) shows a noisy image due to gray-scale compression (a result of poor collimation) and a low-dose technique. The noise impairs demonstration of a complex stenosis at the popliteal trifurcation (arrow). (c) Selective DSA image (oblique view to project the popliteal artery behind the knee replacement) obtained with a higher-dose technique and better collimation shows the complex stenosis at the popliteal trifurcation (arrow) more clearly. There is also a mid-popliteal artery stenosis (obscured by the knee replacement in a and b).
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Edge Filters
Movable edge filters are also useful for producing a more even exposure across the field of view when air opacity has to be included (Figs 4, 6). Although edge filters are useful in this situation, they degrade image quality if placed over the area of interest. Edge filters preferentially remove low-energy photons from the incident beam (beam hardening), thus reducing image contrast. In addition, filters are a source of increased scatter. Because scatter is random, it is not possible to subtract scatter in the mask image from scatter in the contrast-enhanced image; hence, with DSA the effect of filtration-derived scatter is doubled (Fig 1b).
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Patient Positioning
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Demonstration of distal vessels is best achieved by using biplane arteriography. Single-plane imaging may lead to errors in identifying isolated arterial segments, especially when there is superimposition of tibial vessels. Biplane imaging of the calf (lateral with superimposition of the malleoli; posteroanterior with maximum separation of the tibia and fibula) and foot (lateral as for the calf [Fig 4d]; posteroanterior cranial with positioning to separate the metatarsal shafts [Fig 5]) separates the tibial arteries and allows confident identification of isolated segments. To achieve optimal demonstration of foot vessels that are suitable for a DBPG, appropriate positioning of the foot is required.
Pseudo-occlusion is easily produced by excessive plantar flexion (Fig 9). This effect is seen in both diabetic and nondiabetic patients and has real implications for the appropriate choice of management. In diabetes, neuropathic changes in the feet causing tarsal bone dislocation may accentuate or cause compression of the dorsal foot artery (Fig 10), possibly increasing the frequency with which pseudo-occlusion can occur if the proper technique is not used. External compression from patient restraints can also cause pseudo-occlusion (21), and devices used to help maintain proper positioning should be placed with care, preferably outside the field of view, to prevent compression of vessels (Fig 2a).
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Figure 9a. (a) Selective DSA image (lateral view) of the right foot in plantar flexion does not show the dorsal foot artery. As a result, and because of poor target vessels in the calf, the patient was treated medically, without success.
(b) Selective DSA image (lateral view) with the foot in dorsiflexion shows a patent dorsal foot artery. The image was acquired 1 year later with the same contrast material volume and the same angiographic equipment as in a. The patient subsequently underwent successful DBPG placement in the dorsal foot artery.
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Figure 9b. (a) Selective DSA image (lateral view) of the right foot in plantar flexion does not show the dorsal foot artery. As a result, and because of poor target vessels in the calf, the patient was treated medically, without success.
(b) Selective DSA image (lateral view) with the foot in dorsiflexion shows a patent dorsal foot artery. The image was acquired 1 year later with the same contrast material volume and the same angiographic equipment as in a. The patient subsequently underwent successful DBPG placement in the dorsal foot artery.
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Figure 10a. (a) Unsubtracted digital arteriogram (lateral view) of the right foot in plantar flexion in a diabetic patient with severe peripheral neuropathy shows compression of the dorsal foot artery (pseudo-occlusion) by the subluxated talus (arrow). (b) Selective DSA image from the same acquisition shows compression of the dorsal foot artery by the subluxated talus (solid arrow), as well as a more distal stenosis (open arrow). (c) Selective DSA image (lateral view) with the foot in dorsiflexion shows a widely patent proximal dorsal foot artery, thus confirming the presence of a proximal pseudo-occlusion, although the distal stenosis remains.
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Figure 10b. (a) Unsubtracted digital arteriogram (lateral view) of the right foot in plantar flexion in a diabetic patient with severe peripheral neuropathy shows compression of the dorsal foot artery (pseudo-occlusion) by the subluxated talus (arrow). (b) Selective DSA image from the same acquisition shows compression of the dorsal foot artery by the subluxated talus (solid arrow), as well as a more distal stenosis (open arrow). (c) Selective DSA image (lateral view) with the foot in dorsiflexion shows a widely patent proximal dorsal foot artery, thus confirming the presence of a proximal pseudo-occlusion, although the distal stenosis remains.
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Figure 10c. (a) Unsubtracted digital arteriogram (lateral view) of the right foot in plantar flexion in a diabetic patient with severe peripheral neuropathy shows compression of the dorsal foot artery (pseudo-occlusion) by the subluxated talus (arrow). (b) Selective DSA image from the same acquisition shows compression of the dorsal foot artery by the subluxated talus (solid arrow), as well as a more distal stenosis (open arrow). (c) Selective DSA image (lateral view) with the foot in dorsiflexion shows a widely patent proximal dorsal foot artery, thus confirming the presence of a proximal pseudo-occlusion, although the distal stenosis remains.
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A combination of these errors can lead to failure to demonstrate good-sized blood vessels suitable for a DBPG (Fig 11). With careful attention to adequate contrast material injection, positioning, immobilization, collimation, and proper dorsiflexion, it is usually possible to demonstrate vessels in the feet, even if they are not suitable for a DBPG.
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Figure 11a. (a) DSA image (lateral view) obtained at another institution with appropriate positioning of the left foot and no significant patient movement fails to show the foot arteries. This failure is probably due to three factors: inadequate contrast material volume or proximal injection, poor radiographic technique, and old equipment. On the basis of this image, amputation was recommended. (b) Selective DSA image (lateral view) obtained with a good technique and good equipment shows a patent proximal dorsal foot artery (arrow), which is suitable for a DBPG.
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Figure 11b. (a) DSA image (lateral view) obtained at another institution with appropriate positioning of the left foot and no significant patient movement fails to show the foot arteries. This failure is probably due to three factors: inadequate contrast material volume or proximal injection, poor radiographic technique, and old equipment. On the basis of this image, amputation was recommended. (b) Selective DSA image (lateral view) obtained with a good technique and good equipment shows a patent proximal dorsal foot artery (arrow), which is suitable for a DBPG.
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Peripheral Vasodilators
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Patients with severe ischemia obviously have poor blood flow in the distal limb being investigated. However, there is still scope for improving blood flow by using vasodilators, which have a significant effect on image quality. This idea runs contrary to the teaching that there is little scope for increasing blood flow in ischemic limbs because ischemia produces maximum vasodilatation (11). Also, it is stated that giving vasodilators may cause vasodilatation in more proximal vessels, producing worse images due to a steal effect (10). However, worse images are not produced in this situation (Fig 12), as shown in intraarterial Doppler US (22) and comparative angiographic (23) studies. Vasodilatation is particularly important for demonstrating patent vessels distal to a long occlusion.
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Figure 12a. (a) Selective DSA image (lateral view) of the right calf shows opacification of the proximal tibial arteries only (arrow). Delayed imaging showed no further opacification. (b) Selective DSA image obtained after intraarterial injection of papaverine (30 mg) shows filling of the anterior tibial artery (arrow) and peroneal artery (which was not seen previously). The same volume of contrast medium, patient position, and radiographic technique were used as in a.
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Figure 12b. (a) Selective DSA image (lateral view) of the right calf shows opacification of the proximal tibial arteries only (arrow). Delayed imaging showed no further opacification. (b) Selective DSA image obtained after intraarterial injection of papaverine (30 mg) shows filling of the anterior tibial artery (arrow) and peroneal artery (which was not seen previously). The same volume of contrast medium, patient position, and radiographic technique were used as in a.
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The intraarterial vasodilators thought to be appropriate for augmenting blood flow for angiography (although not necessarily approved by the Food and Drug Administration for this application) include nitroglycerin, phentolamine, tolazoline, and papaverine (10,11,23). Although some authors recommend reactive hyperemia to improve flow (10,11), we do not believe that this provides optimum imaging in severe PVD due to its propensity for increasing patient movement (11). Reactive hyperemia is uncomfortable, particularly when applied to an ischemic limb.
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Procedure Safety
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In most patients, selective DSA performed with 30% contrast material and selective use of nonionic contrast media for high-risk patients (10) is very safe. Fears about an increased risk associated with large volumes of contrast material required to perform selective DSA at multiple anatomic levels are without foundation. The amount of contrast material required is equivalent to that required for nonselective arteriography. In our experience with selective DSA in over 1,400 patients from a high-risk population, with good hydration, the frequency of significant renal insufficiency has been low (1.5%). Precipitating or worsening heart failure is also uncommon (occurring in <0.5% of our high-risk population despite vigorous preprocedure hydration). Use of small-diameter catheters (4 or 5 F), such as the Sos Omni Flush (AngioDynamics), and hydrophilic guide wires makes selective cannulation of the contralateral external iliac artery quick and safe. In our experience, no complications have occurred in over 130 selective femoral DSA studies performed with cannulation of the external iliac artery from a contralateral femoral puncture.
In patients with significant heart failure or renal insufficiency, the volume of contrast material used can be reduced by using carbon dioxide as an intravascular contrast agent. Although carbon dioxide may be satisfactory for demonstrating proximal vessels, we have found that in patients with severe PVD, demonstration of vessels distal to severe stenoses or occlusions is poor (Fig 13). When the quality of the carbon dioxide images starts to deteriorate, we recommend changing to conventional contrast material for more distal imaging.
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Figure 13a. (a) Selective DSA image obtained by using 60 mL of carbon dioxide shows a patent right popliteal artery but apparent occlusion or severe stenosis of the proximal tibial arteries. Note the break in the column of carbon dioxide in the upper popliteal artery (arrow). (b) Selective DSA image obtained with 30% contrast material (12 mL administered at 4 mL/sec) in the same position as in a shows improved image quality. The stenoses at the origins of the tibial arteries are shown to be less extensive than in a.
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Figure 13b. (a) Selective DSA image obtained by using 60 mL of carbon dioxide shows a patent right popliteal artery but apparent occlusion or severe stenosis of the proximal tibial arteries. Note the break in the column of carbon dioxide in the upper popliteal artery (arrow). (b) Selective DSA image obtained with 30% contrast material (12 mL administered at 4 mL/sec) in the same position as in a shows improved image quality. The stenoses at the origins of the tibial arteries are shown to be less extensive than in a.
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Conclusions
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In many practices, most patients evaluated for PVD have intermittent claudication due to predominantly supragenicular disease. Conventional arteriography is usually adequate, and it is not necessary to use the selective DSA techniques illustrated herein. However, for patients with severe resting ischemia, especially those with diabetes, high-quality selective DSA is essential to ensure that all distal vessels suitable for a DBPG are identified.
Much has been written about the ability of some noninvasive techniques, particularly MR angiography, to show distal vessels not visible at conventional arteriography. Even before the invention of MR angiography, it was well known that conventional arteriography often failed to show significant distal vessels (16–18). Although there is no doubt t
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Abstract
Introduction
