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Original Report |
1 Department of Radiology, Hacettepe University School of Medicine, Ankara
06100, Turkey.
2 Department of Orthopedic Surgery, Hacettepe University School of Medicine,
Ankara 06100, Turkey.
Received October 24, 2003;
accepted after revision January 18, 2004.
Address correspondence to M. Karcaaltincaba, Seyitgazi Sok. 5/7,
Seyranbaglari, Ankara 06670, Turkey
(musturayk{at}yahoo.com).
Abstract
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CONCLUSION. In pediatric patients, MDCT angiography of the extremities with a short imaging time and a low dose of contrast material is feasible and can be used as a noninvasive alternative to conventional angiography.
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Arterial acquisitions were performed in the craniocaudal direction. For upper extremity studies, a bolus injection was performed in the contralateral upper extremity; for lower extremity studies, a venous injection was performed in the right arm via a 20- to 22-gauge Angiocath. Nonionic iodinated contrast material (300 mg/mL) was injected by a power injector at a rate of 2–3 mL/sec, not to exceed 2 mL/kg of body weight. Bolus duration was matched to duration of acquisition. The contrast dose necessary for each study was calculated by multiplying scanning time by injection rate.
Optimal scanning time was determined using a modified bolus tracking method. In this method, an axial slice was obtained at the proximal aspect of the extremity matching the first slice of the CT angiography study. The region of interest was placed outside the extremity (in the air) and, after a 10-sec delay, axial slices were acquired sequentially. When the contrast material arrived in the extremity artery (determined visually by the on-site radiologist), acquisition was initiated manually by the technician. This method was preferred because of difficulty in locating the region of interest for automatic Hounsfield unit measurement and beginning of scanning in small extremity arteries.
The mean luminal enhancement was calculated by placing the region of interest in the lumen of the artery at every 3 cm to obtain attenuation values in Hounsfield units. When more than one artery was present in the axial section, the mean attenuation values in all arteries were obtained.
Three-dimensional volume-rendered and maximum-intensity-projection images were obtained from axial images at a separate workstation (Leonardo, Siemens Medical Solutions) to display vascular and osseous structures. Indications for CT angiography were vasculitis, preoperative vascular anatomy evaluation, a soft-tissue mass, and postoperative assessment of a repaired arterial injury.
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MDCT angiography of the upper extremity was performed in two patients, one with Volkmann's ischemic contracture and one with suspected stenosis of the ulnar artery with repaired ulnar artery transection for preoperative vascular evaluation. In these patients, ulnar, radial, interosseous, and brachial arteries were visualized. In the patient with Volkmann's ischemic contracture, the distal brachial artery was occluded and was reconstituted by collaterals and a recurrent branch of the deep brachial artery (Figs. 1 and 2).
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MDCT angiography of the lower extremity was performed in two patients, one with a thigh mass and the other with a congenital amniotic band–related leg malformation covering the thigh and leg, for visualization of arterial vascular anatomy (Fig. 3). The popliteal artery and its major branches (anterior and posterior tibial and peroneal arteries) were shown in these patients.
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MDCT angiography of the hand was performed in two patients. Although excellent visualization of the proximal and mid segments of the digital arteries and the distal radial and ulnar arteries was accomplished, the distal segments of the digital arteries were not visualized in these patients, probably because of the small size of the artery (Figs. 4A, 4B and 5). The dominant digital artery supplying the first digit in a patient with polydactyly was visualized on MDCT angiography (Fig. 4A, 4B). Significant venous overlay was noted in the patient with polyarteritis nodosa, but the overlay did not obscure arterial anatomy (Fig. 5).
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Conventional angiography has several disadvantages, including a long procedure time; the need for sedation, postprocedural observation, and arterial catheterization; and potential complications such as dissection and occlusion [7, 8]. Therefore, noninvasive methods for vascular imaging are needed. CT angiography has been used for pediatric applications as an alternative to conventional angiography in the abdomen and chest [7]. Moreover, 3D visualization of the extremity arteries and bones is not possible with conventional digital subtraction angiography.
The technical success rate in our study was 83%, but diagnostic information was obtained in all patients. Optimization of technical parameters—mainly, injection rate, contrast dose, and timing of arterial acquisitions—plays a key role in technical success. We think the use of a preset delay to determine the arrival of contrast material in extremity arteries of pediatric patients is difficult, mainly because of unpredictable circulation times. Therefore, a modified bolus tracking method (described in Materials and Methods) should be preferred in pediatric patients. If bolus-tracking software is not available, a timing minibolus can be used to determine the exact time of arterial phase scanning [3]. In our study, bolus injection duration was matched to duration of arterial acquisition and resulted in adequate enhancement of the arteries. In one patient, significant venous contamination occurred during CT angiography of the hand; however, arteries and veins could be differentiated by their distinct anatomic location in this patient. During CT angiography of the hand, venous return occurs rapidly and fast acquisition is needed to overcome this problem; acquisitions can be obtained faster with 16-MDCT systems.
Three-dimensional volume-rendered visualization of the extremity arteries and their relationship to adjacent bone structures provided important anatomic information to the orthopedic surgeon for preoperative evaluation and treatment of patients with a congenital anomaly, polydactyly, Volkmann's ischemic contracture, suspected arterial stenosis, and occlusion. This technique has been used successfully in adults as an alternative to conventional angiography for preoperative evaluation before microsurgical reconstruction and for evaluation of arteriovenous malformations of the extremities and the hand [8, 9]. Also, MDCT angiography can be used for preoperative evaluation of musculoskeletal masses [10].
MR angiography can also be used for the evaluation of extremity arteries as a noninvasive alternative to conventional angiography. The preference of CT angiography or MR angiography may depend on level of experience or the availability of CT or MR scanners in different institutions. The major advantages of MR angiography are the lack of radiation exposure and the use of nonnephrotoxic gadolinium as a contrast agent. However, the relationship of bones and vessels cannot be adequately displayed on either MR angiography or CT angiography.
Angiographic correlation was not achieved in any of our patients, which may be the main drawback of this study. However, because of ethical concerns (age of the patients, doubling the radiation and contrast dose, and invasiveness of the procedure), angiography was not performed. However, the contrast resolution and visualization of all arterial vessels were adequate in all cases. Surgeons were satisfied with the CT angiography images, and no further conventional angiography was performed. Although radiation exposure, administration of iodine contrast material, the inability to visualize distal arteries such as distal segments of digital arteries, and venous contamination may be considered to be disadvantages of extremity MDCT angiography, no other technique exists to show bone and vessel relationships [6]. Four-MDCT can acquire 1-mm-thick slices at 14 mm/sec table speed. The same anatomic coverage can be scanned with 16-MDCT systems using submillimeter slice thickness (0.62–0.75 mm) in approximately half the imaging time of 4-MDCT using a 1-mm slice thickness [2, 3]. Greater z-axis resolution and faster table speed may lead to improvement of CT angiography of the hands and feet.
In conclusion, MDCT angiography of the extremities is feasible in pediatric patients requiring a low volume of contrast material and can be used for fast noninvasive diagnosis and imaging of arterial pathology and anatomy as an alternative to conventional angiography.
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