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MR Venography Ivan Pedrosa, M.D. Beth Israel Deaconess Medical Center Harvard Medical School Boston, MA Why MR Imaging? • Conventional venography – Multiple injections – I.V. access in affected edematous extremity – Radiation / iodinated contrast • US – Limited in central veins – Limited FOV and anatomic landmarks Why MR Imaging? • CT – Radiation – Iodinated contrast – Pitfalls due to poor opacification / mixing artifacts • Nephrogenic Systemic Fibrosis (NSF) – Increased indications for non-contrast MRV MRV • Techniques – Dark Blood Imaging – Bright Blood Imaging – Gd-enhanced MRV • Clinical Applications – Chest – Abdomen – Pelvis MRV techniques Non-contrast MRV Dark blood Sequences Bright blood Sequences Double IR Spin echo Double IR SSFSE Dynamic SSFSE TOF GRE (Cine) FIESTA (Cine) Phase Contrast Gd-enhanced MRV 3D FS T1-W GRE (VIBE, LAVA, THRIVE) Spin Echo (“dark blood”) 180º 90º 180º 90º HAlf-Fourier Single shot Turbo Spin Echo (HASTE or SSFSE) K space 180º 90º • One second to collect the whole image • Dark blood • Protons exit slice • Slow flow - ↑↑ SI • Thrombus - ↓↑ SI SSFSE/HASTE Dynamic HASTE • Intravascular signal void • Valsalva – intrathoracic P – Venous return • T2 of blood is long VALSALVA Dynamic HASTE • Valsalva – intrathoracic P – Venous return • T2 of blood is long VALSALVA DB HASTE (“dark blood”) 180º 180º 180º 90º TI 180º Double IR T1 FSE IR-T1W Cardiac-gated 1 slice (~16 sec) breath-hold 2 slices with ASSET IR-HASTE ~20 slices ( sec) breath-hold Bright blood Sequences • • • • TOF GRE (Cine) FIESTA (Cine) Phase Contrast Time-of-Flight (TOF) Time-of-Flight (TOF) Time-of-Flight (TOF) Time-of-Flight (TOF) Time-of-Flight (TOF) Time-of-Flight (TOF) Time-of-Flight (TOF) Time-of-Flight (TOF) TOF TOF optimization for slow flow TOF: in-plane saturation Sagittal Axial acquisition Gad-MRV Sagittal TOF optimization for slow flow • Slice perpendicular to vessel of interest • Decrease slice thickness • Cardiac gating? ECG Tracing Blood flow (Pulse Oximeter) Systole (arterial) True FISP / FIESTA / Balanced FFE • True Fast Imaging with Steady-state Precession • Gradients are fully balanced in order to recycle the transverse magnetization in long T2 species • Contrast – T2 / T1 ratio – Blood vessels are bright (T2 of blood is ) True FISP Pros • Fast – Road map • No breathing artifacts • Thrombus – Filling defect SI • Cine True FISP – FIESTA Cons • Artifacts – Pulsatile flow – Off-resonace • Acute / subacute thrombus True FISP True FISP True FISP Gd-enhanced MRV True FISP L True FISP Gd-enhanced MRV Pedrosa I. AJR 2005 Phase Contrast (PC) • 2 equal and opposite Venc gradients between the excitation and echo. • With stationary protons, phase shifts induced by the first gradient are reversed and canceled by the second gradient. • In moving protons, the second gradient does not quite cancel out phase shifts induced by the first gradient • These phase shifts are detected and proportional to the amount of motion in the direction of the encoding gradients Phase Contrast (PC) High velocity flow towards the head (Ascending aorta) Moderate velocity flow towards the head (Pulmonary artery) • Venc gradient applied in the slice (superior-inferior) direction • In the phase (velocity) image – Gray represents stationary background tissues – White represents blood flowing caudally (towards feet) – Black represents blood flowing cranially (towards head) – The intensity of white or black represents the magnitude of velocity in the respective directions Moderate velocity flow towards the feet (SVC) Phase Image High velocity flow towards the feet (Descending aorta) Magnitude Image Phase Contrast (PC) • If Venc is chosen to be too low, aliasing (“wrap-around artifact”) occurs when velocities exceed that value causing velocities to mimic a “lower” value Venc set to 140 cm/sec, appropriate for this volunteer • If Venc is chosen to be too high, sensitivity to slow flow and accuracy of quantitative analysis of velocity/flow are diminished Venc set to 70 cm/sec, too low for this volunteer. Aliasing or “wrap-around” results in the high-velocity flow areas of the aorta. • Venc for venous imaging? – 40-60 cm/sec Phase Images Phase Contrast (PC) Venc = 40 cm/sec Phase Contrast (PC) QuickTime™ and a YUV420 codec decompressor are needed to see this picture. 3D PC Gadolinium-enhanced MRV • Indirect MRV • Direct MRV Indirect Venography • I.V. access in any peripheral vein – Antecubital vein (Right UE) • Gadolinium – Single dose (~20 cc) @ 2 cc/seg – Single dose (~20 cc) @ 0.8 cc/seg – 20 cc saline @ 0.8 cc/seg • 3D GRE T1 • Subtractions – Venogram-like MIP reconstructions Double dose Gd Single injection/dual rate Timing arterial phase QuickTime™ and a decompressor are needed to see this picture. Indirect Venography VENOUS PHASE = ARTERIAL PHASE SUBTRACTION Indirect Venography SUBSTRACTION MIP Direct Venography • I.V. access in affected extremity or bilateral • Gadolinium – 5 cc Gd in 100 cc saline (1:20) • Tourniquet in lower extremities • 3D GRE T1 Li W et al. J Magn Reson Imaging 1998; 8(3): 630-3 Direct Venography Thrombus Characterization – Bland thrombus No enhancement – Variable SI – – Tumor thrombus –Enhancement on Gd-MRV » Subtractions! » Absence of enhancement does NOT exclude tumor thrombus – SI on T2-weighted images Tumor thrombus: Intravenous leiomyomatosis U Staging • Acute thrombus – Enlargement of vein by intraluminal thrombus – SI on T2-weighted images • Vessel wall • Thrombus – Perivascular soft tissue edema – SI on T1-weighted images (subacute) • Chronic thrombus – Vein attenuated or not visible – Venous collaterals – ↓ SI on all sequences Acute thrombosis of the portal vein T2W T1W post-contrast Paget von Schrotter syndrome or “effort” thrombosis Chronic Thrombosis Venous thrombosis Is the thrombosis acute or chronic? Do I need to anticoagulate this patient? Acute/subacute thrombosis brachiocephalic vein: chronic occlusion Central catheter malfunction Fibrin sheath Clinical Indications SVC syndrome Venous Access • Central catheters – – – – Hemodyalisis Chemotherapy Parenteral nutrition Thrombosis in first 3 months (10%) • MRV chest – 15 pts with occlusion or stenosis central veins – Venous access possible in 14 pts Shinde TS et al. Radiology 1999;213:555-560 IVC in Renal Cell Carcinoma QuickTime™ and a YUV420 codec decompressor are needed to see this picture. 51 yo male with PE Papillary carcinoma Pulmonary Embolism Isolated Iliac Vein DVT Conclusion • Central veins of the chest, abdomen and pelvis – Limited evaluation with US • Whole-body venous roadmap – Vascular access • Pregnancy