Clinical Applications

Indications for MR venography of the IVC include assessment of extrinsic or intrinsic caval obstruction, evaluation of congenital anatomic variations and pre-operative or pre-interventional display of venous anatomy.

Thrombosis of the pelvic veins or IVC leads to the development of multiple collateral vessels. In patients with unilateral iliac thrombosis blood may drain to the contralateral side utilizing a wide variety of collaterals including the sacral, rectal, vesical, uterine or prostatic plexus. Complete thrombosis of the IVC leads to drainage of blood into the abdominal epigastric veins and via the thoracic epigastric veins into the SVC. In addition,

Angiography Lower Limb

Fig. 9a-c. Indirect contrast-enhanced 3D MR angiography of the pelvic and lower extremity vessels showing normal arterial and venous anatomy. The data was acquired in an (a) arterial and (b) venous phase following the intravenous injection of 0.3 mmol/kg paramagnetic contrast agent in an antecubital vein. (c) shows the subtracted data set (venous phase minus arterial phase)

Fig. 9a-c. Indirect contrast-enhanced 3D MR angiography of the pelvic and lower extremity vessels showing normal arterial and venous anatomy. The data was acquired in an (a) arterial and (b) venous phase following the intravenous injection of 0.3 mmol/kg paramagnetic contrast agent in an antecubital vein. (c) shows the subtracted data set (venous phase minus arterial phase)

blood may ascend through the vertebral venous plexus to the azygos or hemiazygos veins before finally draining into the SVC. Venous return may also be provided by multiple collateral veins arising in the anterior and posterior pararenal spaces.

Both TOF and PC MR venography approaches are able to depict anatomic variations of the IVC, and pelvic and lower extremity veins (e.g. duplica tions, anomalous course of the left renal vein). For the evaluation of DVT conventional venography is still widely used and is often regarded as the gold standard. Alternatively, duplex ultrasonography has gained widespread acceptance in many institutions. MR venography offers advantages over sonography and conventional venography in pelvic imaging. In a study conducted by Spritzer et al. [20] the frequency of isolated DVT detected with MR venography was higher than that reported in previous studies with sonography or conventional ascending venography.

Differentiation of bland and tumor thrombus within the renal veins or the IVC is better with MR venography than with CT [21]. Based on the enhancement profiles after administration of paramagnetic contrast agent, MR venography enables differentiation of benign from malignant thrombus: malignant thrombus enhances whereas benign thrombus does not. Thus, MR venography has assumed an important role in the staging of renal cell carcinoma and is well suited for evaluating patients with suspected renal vein thrombosis. While conventional MR angiographic techniques are generally well suited for the assessment of renal veins and IVC, additional morphologic information can be obtained with the help of dynamic 3D acquisitions after contrast agent injection.

If peripheral high resolution MR venography is required, the direct MR venography approach with injection of diluted contrast agent into a foot vein can be performed. The technique has been shown to be appropriate for the accurate display of deep and superficial venous morphology, post-throm-botic changes, and varicosities affecting the lower extremity [13].

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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