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Optimization of Multidetector CT Venography Performed with Elastic Stockings on Patients' Lower Extremities: A Preliminary Study of Nonthrombosed Veins

¹ All authors: Department of Radiology, University Hospital, Rue du Bugnon, 1011 Lausanne, Switzerland.

Received July 10, 2002; accepted after revision September 12, 2002.

 
Address correspondence to Y. Abdelmoumene.

Introduction

Top Introduction Materials and Methods Results Discussion References

 
The combination of CT venography and pulmonary angiography is now widely performed for screening both the pulmonary arteries and the deep veins of the lower limbs and pelvis to diagnose pulmonary embolism and deep venous thrombosis. Many parameters, such as cardiac output, peripheral arterial disease, and dehydration, limit venous enhancement. The objective of this study was to find a way to increase venous enhancement without increasing the iodine dose.

By compressing superficial veins, elastic stockings might improve deep venous enhancement and, as a result, increase diagnostic performance. This technique commonly used in conventional venography to increase deep vein opacification [1] has not been tested on CT venography. The aim of this prospective and preliminary study was to evaluate whether using elastic stockings could increase lower limb deep vein enhancement in patients without deep venous thrombosis.

Materials and Methods

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Materials
Oral informed consent was obtained according to the requirements of the institution's ethics committee. Between April 2, 2000, and July 13, 2000, we prospectively enrolled 60 consecutive patients who underwent pulmonary CT angiography for suspected pulmonary embolism. Among the study population, the first 30 patients, constituting group 1, underwent combined CT venography and pulmonary angiography without elastic stockings. The last 30 patients, constituting group 2, underwent the same examination with elastic stockings. Group 1 consisted of 17 men and 13 women with a mean age of 53 years (range, 21–85 years). Group 2 consisted of 15 men and 15 women with a mean age of 59 years (range, 24–83 years).

CT venography was performed with a LightSpeed QX/i CT scanner (version 3.1; General Electric Medical Systems, Milwaukee, WI). In group 2, we used three sizes of tubular elastic stockings (Tubigrip; Seton Healthcare Group, Oldham, England) selected by the CT technician according to the patient's weight (6.25-cm-diameter bandage for patients with a weight < 65 kg, 7.5-cm-diameter bandage for patients' weight ranging from 65 to 90 kg, and an 8.75-cm-diameter bandage for patients' weight > 90 kg). The stockings were positioned to cover the lower extremities from ankle to mid thigh. CT pulmonary angiography was performed with a single helical acquisition from the cardiac base to the aortic arch during one breath-hold. Scanning began 15–20 sec after the start of the contrast injection depending on the patient's age (15 sec for patients < 60 years old and 20 sec for older patients). CT parameters included 1.25-mm collimation and 7.5-mm/sec table speed using a pitch of 6 (120 kV, 200 mA). The duration of the acquisition was approximately 12 sec, and the number of images obtained was approximately 120. We used an injection protocol of 120 mL of iopentol (Imagopaque [300 mg I/mL]; Nycomed, Munich, Germany) administered through an antecubital vein according to a biphasic injection: 80 mL at 3 mL/sec and 40 mL at 1 mL/sec.

Scanning of the pelvis and the lower limbs began 210 sec after the start of the injection. The venous images were obtained from mid calves to iliac crests, with a 2.5-mm collimation and 7.5-mm/sec table speed, using a pitch of 3, 100 kV, and 170 mA. Five-millimeter-thick images were reconstructed with a 5-mm interval. The duration of this venous imaging was approximately 70 sec, and, according to the patient's height, approximately 220 images were reconstructed.

Methods
Density measurements were obtained by a single radiologist who recorded the venous densities expressed as mean ± standard deviation in Hounsfield units at three levels for each patient: in the popliteal vein just above femoral condyles (Fig. 1), in the superficial femoral vein just before the profound femoral vein ostium, and in the external iliac vein at the level of the sacroiliac joints. A circular region of interest was positioned in the vein so that its diameter was approximately 50% less than the diameter of the vein to reduce partial volume effects on adjacent structures. We did not obtain venous measurements on the thrombosed leg veins and used only the contralateral side for the study. Patients with bilateral deep venous thrombosis were excluded. Density measurements were also not obtained in collapsed veins, defined as flat veins with thicknesses of less than 3 mm. We compared right and left segments in the same patient, using a paired Student's t test. Values obtained in veins of groups 1 and 2 were compared at each level using an unpaired t test. A p value of less than 0.05 was considered significant.

View larger version (111K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1. —62-year-old man with suspected pulmonary embolism. Multidetector CT scan obtained at popliteal level shows region of interest positioned in center of popliteal vein to measure venous density. Note high enhancement due to elastic stockings.

Results

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In group 1, the 30 patients without elastic stockings, 58 density measurements were obtained in the popliteal vein (two measurements were excluded because of unilateral deep venous thrombosis); 50, in the superficial femoral vein (two measurements were excluded because of deep venous thrombosis; three, because of artifacts caused by orthopedic hardware; and five, because of venous collapse); and 57, in the external iliac vein (two measurements were excluded because of deep venous thrombosis and one because of artifacts caused by orthopedic hardware).

Three patients in group 2 were excluded because of the presence of bilateral deep venous thrombosis. In group 2, 47 density measurements were obtained in the popliteal veins (four measurements were excluded because of deep venous thrombosis and three because of venous collapse); 46 measurements, in the superficial femoral veins (four measurements were excluded because of deep venous thrombosis, and four, because of venous collapse); and 49 measurements, in the external iliac veins (four measurements were excluded because of deep venous thrombosis, and one, because of artifact caused by a pelvic catheter).

Our results showed no difference between right- and left-sided venous enhancement, whatever the venous location in each group of patients (p > 0.05). We compared mean venous densities at each level between groups 1 and 2 (Table 1). Mean venous densities were significantly higher at each level in group 2. We obtained a mean increase of venous density of 34%, 32%, and 30%, respectively, at the popliteal, superficial femoral, and external iliac veins.

Discussion

Top Introduction Materials and Methods Results Discussion References

 
Our study shows that elastic stockings increase the venous density by 30–34% compared with that of patients without elastic stockings. This venous opacification improvement invariably increases the density gradient between venous clots and venous flow that could facilitate the detection of deep venous thrombosis. Furthermore, it could allow a reduction of the injected dose of contrast agent. In patients wearing elastic stockings, we obtained higher densities than those reported by other groups, even when they injected a higher dose of contrast material. Loud et al. [2] used a 42-g dose of iodine (120 mL of 350 mg I/mL) and obtained mean venous densities values of 99 H in the inferior vena cava, 94 H in the common femoral vein, and 96 H in the popliteal vein. Cham et al. [3] used a 42-g dose of iodine (300 mg I/mL) and obtained a mean venous density of 101 H in the common femoral vein. Bruce et al. [4] used a 36-g dose of iodine (150 mL of 240 mg I/mL), which is similar to that of our study, and measured mean venous densities ranging from 91 to 97 H at all venous locations that remain inferior to our values [2, 3, 4].

We started the venous acquisition at 210 sec, according to the recommendations of Szapiro et al. [5]. These researchers found that the optimal delay for CT venography is 210 sec, allowing high density both in large veins of the pelvis and in peripheral veins. The optimal dose and contrast injection protocol are still controversial, and different protocols have been used. We chose a biphasic injection because we hypothesized that the second part of the injection, performed at a slow rate, could maintain a high venous enhancement for a longer delay. We do not have a definite argument to prove our hypothesis. However, venous attenuation values in patients without elastic stockings in our study were similar to those reported in published series [2, 3, 4].

In summary, our results show that elastic compression markedly increases deep venous enhancement of the lower limbs. Further studies are needed to show the potential clinical benefit of using elastic stockings for CT venography.

References

Top Introduction Materials and Methods Results Discussion References

 

1. Nylander G. Venography of the lower extremities. In: Abrams HL, ed. Angiography. Boston: Little Brown and Co., 1971: 1251–1271
2. Loud PA, Katz DS, Klippenstein DL, Shah RD, Grossman ZD. Combined CT venography and pulmonary angiography in suspected thromboembolic disease: diagnostic accuracy for deep venous evaluation. AJR 2000;174:61 –65[Abstract/Free Full Text]
3. Cham MD, Yankelevitz DF, Shaham D, Shah AA, Sherman L. Deep venous thrombosis by using CT venography. Radiology 2000;216:744 –751[Abstract/Free Full Text]
4. Bruce D, Loud PA, Klippenstein DL, Grossman ZD, Katz DS. Combined CT venography and pulmonary angiography: how much venous enhancement is routinely obtained? AJR 2001;176:1281 –1285[Abstract/Free Full Text]
5. Szapiro D, Ghaye B, Willems V, Zhang L, Albert A, Dondelinger R. Evaluation of CT time-density curves of lower-limb veins. Invest Radiol 2001;36:164 –169[Medline]

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