CTV and MRV

CTV and MRV

1. Normal Brain CTV and MRV Dr. Yash Kumar Achantani OSR

2. Normal Venous Anatomy The intracranial venous system has two major components, Dural venous sinuses. Cerebral veins. Dural Venous Sinuses Dural venous sinuses are subdivided into Anteroinferior group [ cavernous sinus (CS), superior and inferior petrosal sinuses (SPSs, IPSs), clival venous plexus (CVP), and sphenoparietal sinus ( SphPS ) ]

3. Posterosuperior group [ superior sagittal sinus (SSS), inferior sagittal sinus (ISS), straight sinus (SS), sinus confluence ( torcular herophili ), transverse sinuses (TSs), sigmoid sinuses, and jugular bulbs ] Cerebral Veins The cerebral veins are subdivided into three groups: Superficial ("cortical" or "external") veins Superior Cortical Veins [eight and twelve unnamed superficial veins, vein of Trolard ] Middle Cortical Veins [ superficial middle cerebral vein (SMCV)] Inferior Cortical Veins [ deep middle cerebral vein (DMCV), basal vein of Rosenthal (BVR)]

4. (2) Deep cerebral ("internal") veins, and Medullary veins Subependymal veins, Deep paramedian veins (3) Brainstem/posterior fossa veins. Superior (" galenic ") group [ precentral cerebellar vein (PCV), the superior vermian vein, and the anterior pontomesencephalic vein (APMV)] Anterior (petrosal) group [petrosal vein (PV)] Posterior group [inferior vermian veins]

5. SSS ISS SS TS TH VoG

6. Vein of trolad Vein of Labbe Superficial middle cerebral vein

7. Peripheral (Surface) Brain Drainage Brain surface drainage generally follows a radial pattern. Most of the mid and upper surfaces of the cerebral hemispheres together with their subjacent white matter drain centrifugally (outward) via cortical veins into the SSS. Deep (Central) Brain Drainage The basal ganglia, thalami, and most of the hemispheric white matter all drain centripetally (inward) into the deep cerebral veins. The ICVs, VofG , and SS together drain virtually the entire central core of the brain. The most medial aspects of the temporal lobes, primarily the uncus and the anteromedial hippocampus, also drain into the galenic system via the DMCVs and BVR.

8. Inferolateral ( Perisylvian ) Drainage Parenchyma surrounding the sylvian (lateral cerebral) fissure consists of the frontal, parietal, and temporal opercula plus the insula. This perisylvian part of the brain drains via the SMCV into the SphPS and CS. Posterolateral ( Temporoparietal ) Drainage The posterior temporal lobes and inferolateral aspects of the parietal lobes drain via the SPSs and anastomotic vein of Labbé into the TSs.

9. Superficial parts of the brain (cortex, subcortical white matter) are drained by cortical veins (including the vein of Trolard ) and superior sagittal sinus (shown in green). Central core brain structures (basal ganglia, thalami, internal capsules, lateral and third ventricles) and most of the corona radiata are drained by the deep venous system ( internalcerebral veins, vein of Galen, straight sinus) (red).

10. The veins of Labbé and the transverse sinuses drain the posterior temporal, inferior parietal lobes (yellow). The sphenoparietal and cavernous sinuses drain the area around the sylvian fissures (purple)

11. CT Venography CT venography can be defined as a fast thin section volumetric helical CT examination performed with a time-optimized bolus of contrast medium in order to study the cerebral venous system. To visualize the intracranial veins and sinuses, the examination includes the region from the calvarial vertex down to the first vertebral body. Include the atlas (C1) in the study to ensure incorporation of the origin of the jugular internal veins.

12. Data Acquisition Administer 120 mL of nonionic contrast medium (iodine, 300 mg/mL) at a rate of 3 mL/ sec with a 45-second prescanning delay. A helical scan is performed by scanning caudally from the calvarial vertex to C1. A shorter prescanning delay than 30 seconds increases the risk of a nondiagnostic scan due to insufficient enhancement of the venous structures and flow-related artifacts .

13. Influence of the prescanning delay on sinus enhancement. (a) Axial contrastenhanced CT image obtained with a prescanning delay of 25 seconds shows inadequate enhancement of the sigmoid sinuses and jugular foramina. (b) Axial contrast-enhanced CT image obtained with a prescanning delay of 45 seconds clearly shows a thrombus (arrow) in the right sigmoid sinus.

14. Postprocessing Evaluation of venous structures includes multiplanar (sagittal, coronal and oblique) reformatting on a 3D workstation, in which the loss of information is minimized. First, two-dimensional (2D) MPR images are used to visualize dural venous sinuses and cerebral veins, with adequate window level and width. The source images are displayed with a window higher than or equal to 260 HU and a level of approximately 130 HU to clearly visualize the cerebral veins and dural sinuses as separate from the adjacent bone of the calvaria . Second, 2D maximum intensity projection (MIP) series are created and saved.

15. Optional reformations include 3D MIP and volume rendering display algorithms, which typically require less than 5 minutes. Further postprocessing with a 3D integral display algorithm is performed in cases of cortical venous thrombosis and requires 10–15 minutes. Model Preparation for 3D Display Algorithms Postprocessing is performed with a 3D workstation. For reformation, a graded subtraction is used to remove bone without deleting venous structures. The high attenuation of cortical bone of the skull is isolated first (the mask) without including any veins. The bone model (mask) is then subtracted from the main data set to create a first-phase vascular model.

16. This model contains residual bone, which is similar in attenuation to the vessels. The residual bone can be added to the mask through a process called dilation. Graded subtractions of the dilated bone mask from the vascular model allow complete removal of the skull, typically after 2-pixel dilation of the mask, without sacrificing vascular and soft-tissue detail for the integral display algorithm. Three-Dimensional Display Algorithms The MIP algorithm projects intensity on the viewing screen that is the brightest intensity in the 3D model volume along a ray perpendicular to the viewing screen. This display technique enables one to visualize the high-attenuation vessels through the low-attenuation brain.

17. Normal sinovenous anatomy. Axial MIP CT image (a) and 3D volume-rendered image from CT venography (oblique anterosuperior view) (b) show the internal cerebral veins (ICV) , basal veins of Rosenthal (BVR) , vein of Galen (VOG) , and straight sinus ( StrS ) . On the volume-rendered image, note the asymmetric appearance of the torcular herophili (TH) , which is formed by the union of the superior sagittal sinus (SSS) , straight sinus, and transverse sinuses (TS) . The volume-rendered image also shows the sigmoid sinus (SS) and superficial middle cerebral vein (SMCV) .

18. Sagittal MIP CT image shows the inferior sagittal sinus (ISS) , as well as the internal cerebral vein, superior sagittal sinus, straight sinus, and vein of Galen.

19. Normal sinovenous anatomy. Three dimensional integral image from CT venography (lateral view) shows the anastomotic vein of Trolard (AVOT) draining into the superior sagittal sinus (SSS), the anastomotic vein of Labbe (AVOL) draining into the transverse sinus (TS), and the superficial middle cerebral vein (SMCV).

20. MRV MRV stands for magnetic resonance venography. MRV is used to assess abnormalities in venous drainage of the brain . 2-dimensional (2D) time-of-flight (TOF) MR venography (MRV) and 3-dimensional (3D) phase-contrast (PC) are the technique commonly used to assess the cerebral venous sinuses because they are easy to perform and do not require contrast administration.

21. Time-of-flight (TOF) This technique shows contrast between stationary tissues and flowing blood by manipulating the magnitude of magnetization. The magnitude of magnetization from the moving spins is very large compared to the magnetization from the stationary spins which is relatively small. This leads to a large signal from moving blood spins and a diminished signal from stationary tissue spins. Time of flight (TOF) utilizes the longitudinal magnetization vector for imaging.

22. Phase contrast (PC) These techniques drive contrast between stationary tissues and flowing blood by manipulating the phase of the magnetization. The phase of the magnetization from the stationary spins is zero and the phase of the magnetization from the moving spins is non-zero. The phase is a measure of how far the magnetization process from the time it is tipped into the transverse plane until the time it is detected. A bipolar gradient pulse with equal magnitude and opposite direction is used to diminish signal from the stationary tissue. Phase contrast angiography (PCA) utilises the transverse magnetization vector.

23. In phase difference images, the signal is linearly proportional to the velocity of the spins. Fast moving spins give rise to a larger signal and spins moving in one direction are assigned a bright signal and appear white in the scan , whereas spins moving in the opposite direction are assigned a dark signal and appear black in the scan. Phase contrast methods are sensitive to a range of velocities, so the user must choose this value carefully. Different velocity encoding values can be used in different scans to highlight different vessels. High velocity encoding for arteries (40-70 cm/sec) due to arterial flow is fast.  Low velocity encoding for veins (10-20 cm/sec) due to venous flow is slow. Phase contrast scans can be used for 2D or 3D imaging.

24. Indications for magnetic resonance venography (MRV) brain Evaluation of thrombosis Tumour of the cerebral venous sinus Drowsiness and confusion accompanying a headache

25. Contraindications magnetic resonance venography (MRV) brain Any electrically, magnetically or mechanically activated implant (e.g. cardiac pacemaker, insulin pump biostimulator , neurostimulator , cochlear implant, and hearing aids). Intracranial aneurysm clips (unless made of titanium). Ferromagnetic surgical clips or staples. Metallic foreign body in the eye. Metal shrapnel or bullet.

26. Patient preparation magnetic resonance venography (MRV) brain A satisfactory written consent form must be taken from the patient before entering the scanner room Ask the patient to remove all metal objects. Explain the procedure to the patient Instruct the patient to keep still Positioning magnetic resonance venography (MRV) brain Head first supine Position the head in the head coil and immobilise with cushions Give cushions under the legs for extra comfort Centre the laser beam localizer over the glabella

27. Localiser A three plane localiser must be taken to plan the sequences. Localisers are normally less than 25s. T1 weighted low resolution scans. Suggested protocols, parameters and planning

28. T2 tse axial Plan the axial slices on the sagittal image; angle the position block parallel to the genu and splenium of the corpus callosum. Slices must be sufficient to cover the whole brain from the vertex up to the line of the foramen magnum. Check the positioning block in the other two planes. An appropriate angle must be given in coronal plane on a tilted head (perpendicular to the line of 3rd ventricle and brain stem).

29. 2D time-of-flight (TOF) OR 3D phase-contrast (PC) Plan the sagittal 3D or 2D block on the axial plane; angle the position block 10° to midline of the brain. Check the positioning block in the coronal plane and angle 10° to midline of the brain. This angulation is to reduce the in plane saturation effects. Position the saturation band at the bottom of the block in the sagittal and coronal plane to void the arterial signals. Slices must be sufficient to cover the whole brain from temporal lobe to temporal lobe.

30. Maximum intensity projection (MIP) MIP is the most commonly used post-processing technique in MRI vascular studies. MIP reconstructs a 2D projection image from 3D data by a ray tracing algorithm, which produces an image of white pixels representing the highest intensity signal in that location within the examined volume.

31. 2D TOF vs 3D PC For evaluation of Deep venous structures (ICVs, BVRs, VG, SS, ISS) except TSVs , 3D PC sequence scores over 2D TOF thereby showing that 3D PC is better modality than 2D TOF for viewing structures in this group. When all sinuses considered (SSS, LS, SGS,) except TH , 2D TOF proves to be better over 3D PC sequence. Among the superficial venous system, Trolard veins (VTs) is better appreciated on 2D TOF sequence than on 3D PC sequence. Flow gaps when observed on 2D TOF sequence either in hypoplastic side of TS or area of Torcular Herophili , must be confirmed with 3D PC and T1W CEMRI images.

32. a. In 2D TOF image flow gap is seen in area of junction between Torcular Herophili & Left Lateral Sinus (shown in fig. by arrow). b. In 3D PC image no apparent flow gap visible. c. In Contrast Enhanced - MRI image no apparent flow gap visible which proves the presence of artificial character of flow gap seen on 2D TOF.

33. In 3D PC, MIP and rotational reconstructions without additional post-processing, it is found that intra-cranial venous system assessment is difficult due to interference by presence of arterial system MIP (Maximum Intensity Projection) reconstructions from 3D Phase Contrast showing signals from arterial flow (shown by blue arrows) which interfere assessment of venous structures.

34. A-C, Transverse sinuses were found to be right(A), left(B), and codominant(C). Transverse sinus dominance is a normal variant and is seen very often. Right TS dominance > Left TS dominance > Co-dominant TS

35. MIP (Maximum Intensity Projection) reconstructions, obtained from post-contrast T1 weighted sequence, in Sagittal plane(a), Coronal plane(b), axial plane(c) showing various venous structures included in study. (SSS- Superior Sagittal Sinus, ISS- Inferior Sagittal Sinus, VT- Trolard Vein, TSVs- Thalomostriate Veins, ICVs- Internal Cerebral Veins, VG- Vein of Galen, SS- Straight Sinus, BVRs- Basal Veins of Rosenthal, TH Torcular Herophili , SGS( r,l )- Sigmoid Sinus(right, left), LS( r,l )- Lateral Sinus(right, left))

36. CTV MRV Takes less time Takes more time Comparatively cheaper Costlier Requires Contrast No contrast required Not affected by flow related artefacts Affected by flow related artefacts. Has an advantage over MRV in uncooperative patients. Can not be performed in un cooperative patients. Uses Ionizing radiation No ionising radiation Less sensitive for determining Cortical venous infarcts. More sensitive for determining Cortical venous infarcts.