MR Venography

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IX Ruehm 6-06-2005 19:20 Pagina 331

IX MR Venography

Stefan G. Ruehm

Introduction niques are rather time consuming and of limited use in the presence of inordinately slow flow or The ability of MR imaging to depict flow, in com- tortuous venous anatomy, the use of contrast-en- bination with the inherent soft tissue contrast, has hanced 3D MR venography has been proposed to led to the rapid clinical implementation of this overcome these limitations. modality for vascular imaging. Slower flow and more homogeneous flow profiles make MR venography technically less demanding than MR arteri- Time-of-Flight MR Venography ography. Since venous pathology usually tends to be more extensive, high resolution MR imaging is Time-of-Flight (TOF) MR angiography is based on not required for routine MR venography to the a GRE sequence with rapid succession of alpha same extent as it is needed for imaging of the arte- pulses and short repetition times (TR). Thus the rial system. Conventional time-of-flight (TOF) and signal of stationary tissue is suppressed, whereas phase contrast (PC) MR techniques, which do not flowing spins in the vessel are consistently re- require the use of a paramagnetic contrast agent, freshed. Two-dimensional (2D) or three-dimen- have therefore evolved as reliable and clinically ac- sional (3D) TOF images with bright intravascular cepted methods for assessment of the venous sys- signal can be obtained (Fig. 1) [2-4]. For vessels tem. However, these techniques do have limitations coursing within the acquired section (“in-plane in that they are susceptible to pulsatility, in-plane flow”), the inflow effect becomes less effective. In- saturation effects, and spin dephasing when lami- travascular signal may be reduced to the level of nar flow is disturbed. Furthermore, lengthy acqui- surrounding stationary spins, prohibiting differen- sition times coupled with the technique’s inability tiation of flowing blood from stationary tissues. to reliably display small deep veins in the calf or Potential difficulties in TOF MR venography may superficial and perforating veins running horizon- therefore arise in situations where longer vessel tal to the imaging plane have restricted the routine sections lie within the imaged section. clinical application of conventional MR techniques Since vessels appear bright on TOF MR venog- [1]. To overcome these limitations, the use of con- raphy independently of flow direction, differentia- trast-enhanced three-dimensional (3D) contrast- tion of arteries from veins can be difficult. Flow in enhanced MR venography has been suggested and a particular direction can, however be saturated by is now used with increasing frequency in many in- using spatial flow presaturation bands (Fig. 2). stitutions. Spins being washed into the section from the pre- saturated area do not carry any magnetization, resulting in a lack of inflow enhancement [5]. These Techniques for MR Venography saturation bands can thus be used to obtain selective TOF arteriograms or venograms. Both TOF and PC MR venography sequences have Commonly, two types of 2D TOF sequences are been employed for morphological evaluation of used for MR venography. The first type (spoiled the vascular system. Although they have limited sequences) relies on the inflow of blood alone to applicability for assessment of the arterial system, create vascular signal. FLASH (fast low angle shot) they remain valuable for assessment of the portal [6] and spoiled GRASS (gradient-recalled acquisi- and systemic venous systems. Since these tech- tion in a steady state) sequences belong to this cat- IX Ruehm 6-06-2005 19:20 Pagina 332

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a b

Fig. 1a, b. Maximum Intensity Projection (MIP) display of pelvic venous anatomy based on a 2D MR venography protocol with single slice acquisition in the transverse plain. a Regular display of venous anatomy. b Missing visualization of left internal iliac vein (arrow) due to thrombosis

a b

Fig. 2a, b. MIP display (inferior view) of TOF MR angiography of pelvic vasculature with selective visualization of flow from (a) superior to inferior (arteries) and (b) inferior to superior (veins) using presaturation bands

egory.With the second type of sequence some T2*- msec (on a 1.5 T magnet) has been proposed so that weighting is associated resulting in additional the signal from water and fat are out of phase to en- brightness of the blood vessels. However, station- able the signal from fat to be reduced. ary tissues containing fluid, such as bowel or blad- Selection of the appropriate flip angle is impor- der, may also be bright. FISP (fast imaging se- tant. Too large a flip angle may lead to saturation of quence with partial refocusing) sequences are in- the venous signal, whereas too small a flip angle cluded in this category, as are GRASS sequences as results in noisy images. The best flip angle depends well. When imaging is performed to study deep on whether the image slice is oriented perpendicu- vein thrombosis (DVT) spoiled sequences are usu- lar or parallel to the axis of the vessel. For longitu- ally employed. dinal flow an angle of 20°to 25° is regarded as ap- Blood brightness can be increased by using propriate, whereas an angle of 45°should be cho- longer repetition times (TR). Increasing the TR re- sen for imaging in the transverse plane. sults in an increased number of relaxed spins enter- Image slices need not be contiguous if only a ing the imaging plane. This is accomplished, howev- survey of the venous system is desired. However, er, at the cost of a longer acquisition time. The echo thin contiguous or overlapping slices are required time (TE) should be short although the exact value if Maximum Intensity Projection (MIP) images is not defined and is of minor importance.A TE of 8 need to be calculated. IX Ruehm 6-06-2005 19:20 Pagina 333

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Phase-Contrast MR Venography traction requires the acquisition of pre- and post- contrast data. Image subtraction works less well in Phase-contrast (PC) MR venography is based on the chest and abdomen due to potential spatial the observation that spins moving through a mag- misregistration artifacts caused by respiratory netic field gradient acquire a different phase motion. The advantage of the indirect approach is (phase shift) as compared with static spins. For PC that there is no requirement for direct cannulation imaging two interleaved views are acquired over of the vein in the affected extremity. successive TRs. There is only one difference be- For the direct approach diluted paramagnetic tween the two views: the second view has an added contrast agent is continuously injected upstream bipolar gradient along one direction [7]. This on the side of the affected extremity. This approach bipolar gradient only affects moving spins which permits a full display of the deep and superficial acquire a different phase based on their specific venous system in a manner similar to that achieved flow characteristics. The difference between the with conventional venography. Compared to the in- phase data of the two successively acquired images direct approach the direct injection technique re- is thus limited to phase shifts from moving spins.A sults in superior CNR values although considerably true velocity map is therefore acquired. The meas- less contrast agent is required. To avoid T2-short- ured phase difference in individual pixels with ening effects the dilution factor should be in the flow is directly related to the flow velocity along range of 1:10-20.The 3D data set should be collect- the direction of the first moment change, which is ed during contrast administration. Repeated acqui- referred to as the “velocity-encoded direction”, sitions can be performed, e.g. with and without and which may be along the x-, y-, or z-axis. By placement of a tourniquet or with the extremity in convention, flow is bright if it flows from right to different positions to evaluate for functional ob- left (x-plane), anterior to posterior (y-plane) and struction of veins [12, 13], e.g. in patients with sus- superior to inferior (z-plane). Flow in the opposite pected thoracic outlet syndrome. direction is depicted as black. The technique is The use of a surface coil to increase signal-to- unique in the sense that it is a direct velocity map, noise ratio (SNR) and resolution is advantageous. in which the voxel intensity values are proportion- For data collection, a 3D data set with very short TR al to the actual flow velocity in a particular flow di- and TE values and a flip angle of 30-40°should be rection. The flow sensitivity can be adjusted. The used. Imaging should start following the injection “velocity encoding value” (VENC) helps to deter- of the first 50-60 ml of diluted contrast agent. To al- mine the largest measurable velocity. The appro- low for continuous contrast agent infusion, a tubing priate VENC value should be chosen to exceed the set is helpful which permits the simultaneous at- maximum expected velocity by about 25%. For tachment of two 60 ml syringes. Contrast agent in- some time PC imaging was the preferred MR tech- jection should continue during data collection with nique for assessing the portal venous system [8] sequential k-space filling. This enables central k- since it permitted direct quantitative characteriza- lines to be acquired in the middle of the data acqui- tion of flow dynamics over time [9]. sition and helps avoid artifacts arising from chang- ing gadolinium concentration. In addition, this approach allows more time for filling of venous collat- 3D Contrast-Enhanced MR erals in the presence of a venous occlusion. Venography Techniques Direct Thrombus Imaging Contrast-enhanced MR venography can be performed using an indirect or direct approach. For In contrast to most imaging techniques, which de- the indirect approach, contrast agent is usually ad- lineate thrombus as flow void or contrast filling de- ministered via an antecubital vein and imaging is fect, magnetic resonance direct thrombus imaging performed during the equilibrium contrast phase visualizes thrombus against a suppressed back- [10, 11]. Typically a large dose is required since the ground (Fig. 3). During the process of thrombus contrast agent undergoes considerable dilution be- formation, a predictable reduction in the T1 value fore it reaches the venous vascular territory under of the clot occurs reflecting the presence of methe- investigation. Images should be obtained in the moglobin. High signal intensity occurs initially at early equilibrium phase to avoid significant redis- the periphery of the clot which, over time, extends tribution of the contrast agent in the extracellular toward the center. In addition to the signal generat- fluid compartment. ed by the thrombus itself, further contrast of a clot Typically, image subtraction needs to be per- against blood can be created by nulling the unclot- formed to improve the contrast-to-noise ratio ted blood signal using an inversion recovery pulse. (CNR) of vessels versus background in order to Background signal on the T1-weighted image can improve the quality of the 3D displays. Image sub- be further suppressed through selective radio-fre- IX Ruehm 6-06-2005 19:20 Pagina 334

334 Magnetic Resonance Angiography

plays because the vein enters the slice obliquely. Similarly, compression of a vein by an adjacent structure may be mistaken for thrombus on both non-contrast-enhanced and contrast-enhanced techniques alike. It is therefore mandatory to scru- tinize the source images rather than to simply rely on MIP displays alone. Some patients show exaggerated respiratory variations in venous flow. If flow sensitive TOF MR venography is used the vein will appear dark if the central part of the acquisition is obtained while the venous flow is substantially reduced during exhala- tion. Under these circumstances data acquisition should be performed during breath-holding. The left common iliac vein is compressed as it passes behind the aorta or iliac artery. On TOF MR venography in particular this can be misinterpreted as a stricture or a filling defect on the MIP display. With the direct MR venography technique in- sufficient dilution of the contrast agent will induce T2 and T2* shortening effects resulting in complete signal drop of the venous lumen. To avoid this arti- fact, a standard 0.5 molar extracellular contrast agent should be diluted at least by a factor of 10. In the presence of venous occlusion, the period of contrast agent injection might not be enough to allow complete filling of collateral veins and re- constitution of the leading venous vessel distally to the occlusion. To overcome this potential pitfall, several data sets should be collected during and immediately after infusion of the contrast agent. If the image quality is still inadequate a longer infusion period in combination with a larger contrast agent volume should be used. Venous anatomy may be less predictable than arterial anatomy, especially if collateral veins need a b to be displayed in the presence of post-thrombotic changes. To ensure that all veins are included Fig. 3a, b. Oblique reformatted display of thrombus extending from the calf vein into the politeal vein displayed by (a) direct thicker 3D volumes frequently need to be pre- thrombus imaging (no contrast administration) and (b) indirect scribed. Analysis of a pre-contrast data set can contrast-enhanced MR venography. Whereas the thrombus (ar- help to ensure the complete display of all veins in rows) shows bright signal intensity with the direct thrombus imag- the 3D volume. ing approach, on the contrast enhanced image the thrombus is vi- With the indirect MR venography approach sualized as filling defect timing of the 3D acquisition needs to be planned so that the acquisition of the center of k-space co- quency excitation of water molecules to reduce the incides with the venous phase of the contrast agent fat signal. The technique has been shown to be use- bolus. Adequate image quality is usually obtained ful for the detection of acute DVT [14]. when a large contrast agent dose (0.3 mmol/kg) is used. When image subtraction is employed potential misregistration artifacts due to respiratory Pitfalls and Limitations motion need to be considered.

Interpretation of MR venography for the detection of thrombus is usually based on the depiction of a Superior Vena Cava (SVC) and Upper dark intraluminal defect. On MIP images such a Extremity central filling defect can be masked by the bright signal of blood surrounding the thrombus. On The superior vena cava is (SVC) formed proximally TOF MR venography, reduced intravascular inten- by the confluence of the right and left brachio- sity may be mistaken for thrombus on MIP dis- cephalic veins in the superior mediastinum at the IX Ruehm 6-06-2005 19:20 Pagina 335

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level of the right first costal cartilage. From there, the SVC runs for about 5-7cm inferiorly in a slightly anterior-medial orientation. It ends at the superi- or vena caval orifice in continuity with the right atrium at the level of the third right costal cartilage in the middle mediastinum. Superior to this point it becomes ensheathed by pericardium. Posteriorly, at the level of the second costal cartilage, the azygous vein runs anteriorly over the root of the right lung to merge with the posterior aspect of the SVC. The brachiocephalic veins and the SVC repre- sent the major veins in the superior mediastinum. They drain venous blood from the subclavian veins and internal jugular veins, thus providing venous blood return from both the territories of the upper extremities and the head and neck. The right brachiocephalic vein is shorter than the left brachiocephalic vein. Usually near the con- vergence of the internal jugular vein and the subclavian vein the right brachiocephalic vein receives lymphatic supply from the right lymphatic duct, right jugular lymph trunk and subclavian lymph trunk.At the confluence of left subclavian vein and left internal jugular vein the left brachiocephalic additionally receives the inferior thyroid veins, the thoracic duct, the thymic veins and the superior intercostal vein. The axillary vein is a continuation of the basil- ic vein from the arms. It extends along the chest to the first rib, where it becomes the subclavian vein. The cephalic vein belongs to the superficial venous system of the upper extremity. It merges with the axillary vein just before it becomes the subclavian Fig. 4. Direct contrast-enhanced MR venography of the upper ex- vein. tremity and central thoracic veins. Diluted (1:15) contrast agent was injected into a vein on the dorsum of the hand bilaterally. The data set shows normal filling of the left sided veins. On the right side an occlusion of the axillary/subclavian vein is well depicted. Imaging Techniques Note the prominent collateral veins on right side (arrows) Because of the variable orientation of the chest and upper extremity veins conventional 2D TOF MR venography usually requires data acquisition same time. Acquisition of the imaging data should in variable planes with the scan plane oriented be commenced as soon as half of the contrast vol- perpendicular to the venous vessels in order to ob- ume of the second syringe has been injected. tain adequate image quality. This results in rather Alternatively, the indirect approach (Fig. 5) can long examination times. Contrast-enhanced MR be chosen, with a single injection in an antecubital venography is a particularly well suited technique vein in combination with the acquisition of the 3D for this anatomic region and can be especially ad- data set in the equilibrium contrast phase. The in- vantageous in patients with impaired renal func- direct approach is especially useful in patients for tion, who have a dialysis shunt, fistula or long time whom bilateral venous access is problematic or central catheter placement. For bilateral evaluation when information on both arterial and venous of the axillary, subclavian and brachiocephalic vessels is needed, e.g. when the anastomosis of a veins and for assessment of the superior vena cava, dialysis fistula needs to be displayed. simultaneous injection into the right and left upper extremities can be performed (Fig. 4). Usually two operators are needed for this approach, each Clinical Applications with two 60 ml syringes containing diluted contrast agent. The bilateral injection needs to be co- Indications for MR imaging of the central thoracic ordinated so that both operators complete the in- veins include the investigation of superior vena ca- jection of the first syringe at approximately the va syndrome, assessment of mediastinal abnor- IX Ruehm 6-06-2005 19:20 Pagina 336

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a b

Fig. 5a-d. Indirect contrast-enhanced MR venography of the central thoracic veins. Imaging was performed following the administration of 0.3 mmol/kg paramagnetic contrast agent in the right antecubital vein. 3D data sets were acquired (a) in the arterial and (b) venous phase. A high grade stenosis (arrows) of the superior vena cava is best depicted on the (c) subtracted data set and (d) c d coronal reformatted image

malities with potential vascular involvement, and occur in isolation but is more frequently found in evaluation of anatomical variants such as a left- association with a right SVC. The left SVC com- sided superior vena cava or arteriovenous (AV) monly drains into the coronary sinus or less fre- malformations. MR venography can also be em- quently into the left atrium. ployed to monitor therapeutic success in cases of DVT. Superior vena cava syndrome is characterized Inferior Vena Cava (IVC) and Lower by cyanosis and swelling of the head, neck and Extremity arm in combination with the distension of veins on the neck and trunk. The most common cause Anatomy accounting for approximately 90% of cases is mediastinal neoplastic disease, usually primary or The inferior vena cava (IVC) is a retroperitoneal secondary lung tumors, and lymphoma. The most structure which arises dorsally to the right common common benign causes are mediastinal fibrosis iliac artery from the junction of the right and left and thrombosis secondary to central venous common iliac veins. It ascends posterior to the right catheters or transvenous pacing wires. Obstruc- gonadal artery, the transverse colon, mesenteric tion of any of the major veins which drain into the root, pancreas and duodenum to reach the sulcus SVC may occur as part of thoracic outlet syn- venae cavae on the posterior surface of the liver. It drome. then penetrates the diaphragm to enter the right Persistent left SVC syndrome [15] occurs in atrium. The common iliac veins, lumbar veins, right about 0.3% of the population. It is found with gonadal vein, renal veins, right adrenal vein, higher frequency (ca. 4.3%) in patients with con- phrenic vein and hepatic veins drain into the IVC. genital cardiac disease. Left SVC syndrome may Congenital anomalies of the IVC occur in less IX Ruehm 6-06-2005 19:20 Pagina 337

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Fig. 6a, b. Two-dimensional (2D) TOF MR venography at (a) the level of the inferior vena cava and (b) femoral vein. Thrombus (arrows) in the inferior vena cava and right femoral vein appearing with dark signal intensity is well depicted

than 1% of cases although the incidence is higher Imaging techniques in patients with congenital heart disease. A left- sided IVC is the commonest of these anomalies. In Following the development of gradient echo tech- these patients the left-sided IVC terminates in the niques, TOF MR venography quickly evolved as a left renal vein, which then usually drains into a clinically reliable method for detecting DVT of the normally located distal segment of the IVC.A dou- pelvic and lower extremity veins (Fig. 6) [16-18]. ble IVC is a less frequent finding. The left vena ca- Although TOF venography can detect venous va again usually terminates in the left renal vein thrombosis in the femoral and trifurcation veins but may occasionally drain into the lumbar and [19], lengthy acquisition times have limited its use hemiazygos venous system, the coronary sinus or mainly to the pelvis. Due to in-plane flow satura- the left atrium. The suprarenal segment of a nor- tion preventing reliable depiction of perforating mal or abnormal IVC may occasionally drain into veins which run in the horizontal plane, and the the azygos and hemiazygos vein instead of passing technique’s lack of sensitivity to slow or retrograde through the liver. In the presence of agenesis or flow, TOF MR venography has not been employed hypoplasia of the IVC, blood from the pelvis and for assessing varicose veins or post-thrombotic lower extremities drains mainly into the lumbar, changes. Contrast-enhanced 3D MR venography hemiazygos and azygos veins, which act as collat- overcomes the limitations inherent to TOF venog- eral vessels. raphy. Specifically, direct MR venography with uni- The venous drainage of the lower limbs can be lateral or bilateral injection of diluted paramagnet- anatomically categorized into two separate sys- ic contrast agent allows the display of all vessels, tems - the superficial and deep systems. The deep regardless of the underlying flow characteristics veins usually follow the course of the main arter- and the orientation of the vessel (Fig. 7, 8). Thus ies. In the lower extremity, the deep venous system in-plane saturation is eliminated and imaging includes the superficial and deep femoral veins, along the vessel axis is possible. Perforating and su- the popliteal vein, and the anterior tibial, posterior perficial veins containing slow or even retrograde tibial, and peroneal veins. The veins are commonly flowing blood are fully depicted. The underlying paired at the tibial level, and may, as normal vari- 3D data sets provide high spatial resolution, which ants, be duplicated at the popliteal and femoral lev- permits delineation of very small vessels. els as well. The deep femoral vein, which usually In the pelvic veins, dilution from draining ve- lies in the upper two-thirds of the calf, may con- nous tributaries can cause a reduction of the very nect with its lower part and with the superficial bright signal. Thus for display of the pelvic veins femoral or popliteal veins. and IVC by means of the direct MR venography The greater saphenous vein is the longest su- technique, it is of advantage to use a slightly lower perficial vein. It runs from the dorsal arch of the dilution of the contrast agent, e.g. a dilution of 1:10. foot medial to the tibia up the medial thigh to the Whereas the indirect “equilibrium” MR venogra- femoral vein. The lesser saphenous vein runs from phy approach is commonly sufficient for the diag- the lateral arch of the foot postero-laterally in the nostic display of pelvic veins and IVC (Fig. 9), the calf to join the popliteal vein. Beyond being used direct imaging approach usually results in superior as graft vessels for arterial bypass procedures, the CNR which translates into better image quality and superficial venous system is an important collater- a more detailed depiction of the more peripheral al pathway in the event of DVT. venous anatomy. IX Ruehm 6-06-2005 19:20 Pagina 338

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Fig. 8. Direct contrast-enhanced MR venography following bilateral injection of diluted contrast agent into a dorsal pedal vein showing marked postthrombotic changes on the right side with collateralization (arrows) via superficial veins. The left leg shows normal deep venous anatomy

Fig. 7. Direct contrast-enhanced MR venography of the veins of the upper thigh, and pelvis as well as of the inferior vena cava. A filling defect in the left proximal iliac vein (arrow) is present in the region where the right common iliac artery crosses anteriorly. Pelvic suprapubic and retroperitoneal collaterals are visualized. Normal drainage of the right pelvic veins into the inferior vena cava is visualized

Clinical Applications the development of multiple collateral vessels. In patients with unilateral iliac thrombosis blood Indications for MR venography of the IVC include may drain to the contralateral side utilizing a wide assessment of extrinsic or intrinsic caval obstruc- variety of collaterals including the sacral, rectal, tion, evaluation of congenital anatomic variations vesical, uterine or prostatic plexus. Complete and pre-operative or pre-interventional display of thrombosis of the IVC leads to drainage of blood venous anatomy. into the abdominal epigastric veins and via the Thrombosis of the pelvic veins or IVC leads to thoracic epigastric veins into the SVC. In addition, IX Ruehm 6-06-2005 19:20 Pagina 339

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a b c

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 tions, anomalous course of the left renal vein). For plexus to the azygos or hemiazygos veins before fi- the evaluation of DVT conventional venography is nally draining into the SVC.Venous return may al- still widely used and is often regarded as the gold so be provided by multiple collateral veins arising standard. Alternatively, duplex ultrasonography in the anterior and posterior pararenal spaces. has gained widespread acceptance in many institu- Both TOF and PC MR venography approaches tions. MR venography offers advantages over are able to depict anatomic variations of the IVC, sonography and conventional venography in and pelvic and lower extremity veins (e.g. duplica- pelvic imaging. In a study conducted by Spritzer et IX Ruehm 6-06-2005 19:20 Pagina 340

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al. [20] the frequency of isolated DVT detected dients in NMR imaging. Magn Reson Imaging 2:335- with MR venography was higher than that report- 340 ed in previous studies with sonography or conven- 8. Edelman RR, Zhao B, Liu C et al (1989) MR angiog- tional ascending venography. raphy and dynamic flow evaluation of the portal venous system [see comments]. AJR Am J Roentgenol Differentiation of bland and tumor thrombus 153:755-760 within the renal veins or the IVC is better with MR 9. Pelc NJ, Herfkens RJ, Shimakawa A et al (1991) venography than with CT [21]. Based on the en- Phase contrast cine magnetic resonance imaging. hancement profiles after administration of para- Magn Reson Q 7:229-254 magnetic contrast agent, MR venography enables 10. Lebowitz JA, Rofsky NM, Krinsky GA et al (1997) differentiation of benign from malignant throm- Gadolinium-enhanced body MR venography with bus: malignant thrombus enhances whereas be- subtraction technique. AJR Am J Roentgenol 169:755-758 nign thrombus does not. Thus, MR venography 11. Shinde TS, Lee VS, Rofsky NM et al (1999) Three-di- has assumed an important role in the staging of mensional gadolinium-enhanced MR venographic renal cell carcinoma and is well suited for evaluat- evaluation of patency of central veins in the thorax: ing patients with suspected renal vein thrombosis. initial experience [In Process Citation]. Radiology While conventional MR angiographic techniques 213:555-560 are generally well suited for the assessment of re- 12. Ruehm S, Zimny K, Debatin J (2001) Direct con- nal veins and IVC, additional morphologic infor- trast-enhanced 3D MR venography. Eur. Radiol mation can be obtained with the help of dynamic 11:102-112 13. Ruehm SG, Wiesner W, Debatin JF (2000) Pelvic and 3D acquisitions after contrast agent injection. Lower Extremity Veins: Contrast-enhanced Three- If peripheral high resolution MR venography is dimensional MR Venography with a Dedicated Vas- required, the direct MR venography approach with cular Coil-Initial Experience. Radiology 215:421-427 injection of diluted contrast agent into a foot vein 14. Moody AR, Pollock JG, O’Connor AR et al (1998) can be performed. The technique has been shown Lower-limb deep venous thrombosis: direct MR im- to be appropriate for the accurate display of deep aging of the thrombus. Radiology 209:349-355 and superficial venous morphology, post-throm- 15. Smith DE, Doherty TM, Reynolds GT et al (1996) Subclavian vein anatomic subtypes defined by digi- botic changes, and varicosities affecting the lower tal cinefluroscopic venography prior to permanent extremity [13]. pacemaker lead insertion. Cathet Cardiovasc Diagn 37:252-257 16. Lanzer P, Gross GM, Keller FS et al (1991) Sequen- tial 2D inflow venography: initial clinical observa- References tions. Magn Reson Med 19:470-476 17. Spritzer CE, Sostman HD, Wilkes DC et al (1990) 1. Holtz DJ, Debatin JF, McKinnon GC et al (1996) MR Deep venous thrombosis: experience with gradient- venography of the calf: value of flow-enhanced echo MR imaging in 66 patients. Radiology 177:235- time-of-flight echoplanar imaging. AJR Am J 241 Roentgenol 166:663-668 18. Erdman WA, Weinreb JC, Cohen JM et al (1986) Ve- 2. Bradley WG, Jr, Waluch V (1985) Blood flow: mag- nous thrombosis: clinical and experimental MR im- netic resonance imaging. Radiology 154:443-450 aging. Radiology 161:233-238 3. Dumoulin CL, Hart HR Jr (1986) Magnetic reso- 19. Evans AJ, Sostman HD, Knelson MH et al (1993) nance angiography. Radiology 161:717-720 1992 ARRS Executive Council Award. Detection of 4. Edelman RR, Wentz KU, Mattle H et al (1989) Pro- deep venous thrombosis: prospective comparison of jection arteriography and venography: initial clini- MR imaging with contrast venography. AJR Am J cal results with MR. Radiology 172:351-357 Roentgenol 161:131-139 5. Lenz GW, Haacke EM, Masaryk TJ et al (1988) In- 20. Spritzer CE, Arata MA, Freed KS (2001) Isolated plane vascular imaging: pulse sequence design and pelvic deep venous thrombosis: relative frequency strategy. Radiology 166:875-882 as detected with MR imaging. Radiology 219:521- 6. Frahm J, Merboldt KD, Hanicke W et al (1988) 525 Rapid line scan NMR angiography. Magn Reson 21. Roubidoux MA, Dunnick NR, Sostman HD et al Med 7:79-87 (1992) Renal carcinoma: detection of venous exten- 7. Constantinesco A, Mallet JJ, Bonmartin A et al sion with gradient-echo MR imaging. Radiology (1984) Spatial or flow velocity phase encoding gra- 182:269-272