Evaluation of marrow perfusion in the femoral head by dynamic magnetic resonance imaging. Effect of venous occlusion in a dog model

Abstract

Rationale and objectives: There is a continuing need for a greater sensitivity of magnetic resonance imaging (MRI) in the diagnosis of avascular necrosis (AVN). Previously, it was demonstrated that a dynamic MRI method, with gadolinium-DTPA (Gd-DTPA) enhancement, can detect acute changes not seen on spin-echo images after arterial occlusion in a dog model. Because venous congestion appears to be a more directly relevant hemodynamic abnormality in a majority of clinical AVN cases, the authors extended the dynamic MRI technique to study changes in venous occlusion.

Methods: Dynamic MRI of the proximal femur was performed in five adult dogs before and after unilateral ligation of common iliac and lateral circumflex veins. Sixteen sequential gradient-recalled pulse sequence (GRASS) images (time resolution = 45 mseconds, echo time = 9 mseconds, flip angle = 65 degrees) were obtained immediately after a bolus intravenous injection of 0.2 mmol/kg of Gd-DTPA. Simultaneous measurements of regional blood flow were made using the radioactive microsphere method.

Results: After venous ligation, there was a 25% to 45% decrease in the degree of enhancement compared with preligation values on the ligated side. The decrease in cumulative enhancement (integrated over the entire time course) was statistically significant. The occlusion technique was verified by confirming a statistically significant decrease in blood flow determined by the microsphere method.

Conclusions: Dynamic Gd-DTPA-enhanced fast MRI technique can detect acute changes in bone marrow perfusion due to venous occlusion. This technique may have applications in the early detection of nontraumatic AVN.

Fig. 1

Diagram shows the regions of interest used in obtaining signal intensity: (A) proximal femoral head; (B) distal femoral head; and (C) femoral neck. The orientation is the same as in Figure 2.

Fig. 2

An axial T1-weighted spin-echo image at the level of the femoral head and neck in a normal dog (TR/TE = 500/20). The orientation is the same as in Figure 1. Marrow is predominantly fatty in the proximal femoral head (small open arrow) and predominantly hematopoietic distal to the physeal line (large open arrow).

Figs. 3A and 3B

Selected axial images at the level of the femoral head and neck in a normal dog after gadolinium-DTPA administration before (A) and after (B) venous occlusion on the left side. Images were obtained at 0 (top left), 46 (top right), 92 (bottom left), and 138 (bottom right) seconds after gadolinium administration. Bilateral enhancement is seen in the distal femoral head and femoral neck after contrast administration (arrows). After unilateral venous ligation, enhancement still appears bilaterally symmetric; however, quantitative analysis shows a statistically significant change (see Results section). Quantitative enhancement also is seen in the proximal femoral head (Fig. 3).

Figs. 4A-4F

Percent enhancement versus time after Gd injection for each anatomic region. Curves before and after unilateral ligation are compared. A rapid rise followed by a slower decrease is seen. There is 25% to 45% reduction in percent enhancement after venous occlusion on the ligated side. Proximal portion of the femoral head on the right (control) (A) side and left (ligation) side. (B) Distal portion of the femoral head on the right (control) (C) side and left (ligation) (D) side. Femoral neck on the right (control) (E) side and left (ligation) (F) side.

Fig. 5

Percent change in total percent enhancement after ligation (see Methods section for definition). A statistically significant decrease was noted for all three regions after ligation. The black bars represent the left (ligation) side; the shaded bars represent the right (control) side.

Fig. 6

Percent change in regional blood flow after ligation determined by the radioactive microsphere method. The statistically significant decrease on the ligated side validates our occlusion method. Shaded bars represent the left (ligation) side; open bars represent the right (control) side.

Fig. 7

Magnetic resonance imaging total percent enhancement versus microsphere blood flow data for one dog. The correlation coefficient for linear regression for this dog is 0.86.