MRA AND MRV MAGNETIC RESONANCE IMAGING.pptx

MRA AND MRV OF THE BRAIN

1. MRA AND MRV MOUNICA.K

2. MRA-MAGNETIC RESONANCE ANGIOGRAPHY MRV- MAGNETIC RESONANCE VENOGRAPHY

3. INTRODUCTION Magnetic resonance angiography is an alternative to conventional angiography and CT angiography, eliminating the need for ionizing radiation and iodinated contrast media, and sometimes contrast media altogether. MR ANGIOGRAPHY CONVENTIONAL ANGIO NON INVASIVE INVASIVE NO CONTRAST REQUIRED NEPHROTOXIC CONTRAST NON IONISING IONISING RADIATIONS

4. TYPES OF MRA It has evolved into several techniques with different advantages and applications: Contrast-enhanced MR angiography Non-contrast enhanced MR angiography

5. NON CONTRAST ENHANCED MRA There are different ways to create MRA (Magnetic Resonance Angiography) images. Two common methods Time-of-Flight (TOF) MRA Phase-Contrast (PC) MRA Doesn’t require contrast dye. Instead, they rely on the natural differences between moving blood and stationary tissue.

6. TOF-MRA: 2D TOF-MRA : Takes thin, stacked images (about 1.5 mm thick) across the vessel direction. It works well for detecting slow blood flow. 3D TOF-MRA : Scans thicker sections and slices them into thinner images (less than 1 mm) to create a 3D image. This method gives better detail and is good for small or twisted vessels. However, blood moving through the entire slab can lose contrast, making some vessels harder to see. One limitation of TOF-MRA is that non-moving tissues (like clots) can sometimes look like flowing blood.

7. PC-MRA: PC-MRA helps avoid this problem by using two sets of images and subtracting them to remove signals from stationary tissue. This shows only flowing blood and also provides details like how much blood is flowing and in which direction. 2D PC-MRA : Uses gradients in 2 or 3 directions to show blood vessels clearly. 3D PC-MRA : Offers even better resolution and can measure flow direction in all three axes. It creates a "speed image" where brighter areas mean faster blood flow. Both TOF and PC-MRA data can be processed using a technique called MIP (Maximum Intensity Projection) to create clear 3D images of the vessels.

8. CONTRAST-ENHANCED MRA (CE-MRA) Contrast-Enhanced MRA (CE-MRA) uses a contrast agent (gadolinium) to make blood vessels stand out more clearly, especially when blood flow is slow. A gadolinium injection is given through a vein (0.1–0.3 mmol/kg). As it travels through the bloodstream, scans are done to capture images when the contrast is in the arteries. This is called the first-pass method . Digital subtraction MRA : This removes background tissues by subtracting a pre-contrast image from a post-contrast one, improving vessel visibility.

9. ADVANTAGES OF CE-MRA: Faster scans than TOF-MRA (better temporal resolution ) Clearer images even in slow-flow vessels Higher quality imaging with newer scanners: 3.0 Tesla (3T) and 7 Tesla (7T) MRI machines improve image clarity (better signal-to-noise ratio) Parallel imaging at higher field strengths reduces scan time, increases detail, and covers more anatomy

10. INDICATIONS To evaluate the conditions of the carotid arteries, such as Stenotic/occlusive disease in symptomatic patients. Stenotic/occlusive disease in asymptomatic members when the Doppler scan is abnormal. Aneurysms Cervicocranial arterial dissection in members with suggestive signs or symptoms, i.e., unilateral headache, oculosympathetic palsy, amaurosis fugax, and symptoms of focal brain ischemia

11. 2. To rule out an intracranial aneurysm, including an aneurysm of the circle of Willis 3. Screening for intracranial aneurysm in neurofibromatosis, Ehlers-Danlos syndrome 4. Evaluation of tinnitus of vascular etiology 5. Evaluation of known vasculitides 6. Preoperative evaluation of brain surgery 7. Postoperative follow-up 8. As a follow-up study of arteriovenous malformation

12. Blood supply of the brain

13. ANTERIOR CIRCULATION

14. INTERNAL CAROTID ARTERY The  internal carotid artery (ICA)  is one of the two terminal branches of the common carotid artery(CCA) , which supplies the intracranial structures. There are seven segments C1: cervical segment C2: petrous (horizontal) segment C3: lacerum segment C4: cavernous segment C5: clinoid segment C6: ophthalmic ( supraclinoid ) segment C7: communicating (terminal) segment

15. VARIANT ANATOMY Aberrant ICA Congenital absence of the ICA Retropharyngeal course, called kissing carotids when bilateral Persistent carotid-vertebrobasilar anastomoses Lateralized internal carotid artery

16. Congenital hypoplasia of ica

17. ANTERIOR CEREBRAL ARTERY Origin: T ermination of the internal carotid artery Course: F rom the medial end of the lateral fissure stem to the corpus callosum Main branches Anterior communicating artery Medial lenticulostriate arteries Recurrent artery of Heubner Supply:  the corpus callosum, the septum pellucidum, the putamen (anterior portion), the head of the caudate nucleus, and parts of the internal capsule

18. SEGMENTS OF ACA A1: horizontal or pre-communicating segment originating ICA bifurcation to ACOM A2: vertical, post-communicating or infracallosal segment From acom to callosomarginal artery i.e., junction of rostrum and genu of corpus callosum A3:  precallosal segment distal to the origin of the callosomarginal artery Terminates where the artery turns directly posterior above the body of the corpus callosum A4:  supracallosal segment Above the body of the corpus callosum, anterior to the plane of the coronal suture A5: ​ postcallosal segment Above the body of the corpus callosum, posterior to the plane of the coronal suture

19. NORMAL VARIATION AND ANOMALIES OF ACA Common 1. Hypoplastic or absent a1 2. Bihemispheric ACA 3. Acoa can be absent, fenestrated, or duplicated Anomalies 1. Azygous ACA-single ACA, ACOA absent 2. Infraoptic ACA –A1 passes under the optic nerve

20. Aplastic A1

21. MIDDLE CEREBRAL ARTERY The  middle cerebral artery  ( MCA ) is one of the three major paired arteries that supply blood to the brain. The MCA arises from the internal carotid artery as the larger of the two main terminal branches Segments The MCA is divided into four segments: 1. Horizontal 2. Insular 3. Opercular 4. cortical

22. M1: sphenoidal or horizontal segment from the terminal ICA to the sylvian fissure M2: insular segment from post-bifurcation to the top of the sylvian fissure M3: opercular segment originates at the circular sulcus of the insula courses laterally along the frontoparietal operculum terminates at the external/superior surface of the Sylvian fissure M4: cortical segment originates at the external/top surface of the Sylvian fissure courses superiorly on the lateral convexity terminates at their final cortical territory

23. The middle cerebral arteries supply the majority of the lateral surface of the hemisphere, except the superior portion of the parietal lobe(via the anterior cerebral artery)  and the inferior portion of the temporal lobe and occipital lobe(via the posterior cerebral artery). In addition, the middle cerebral arteries supply part of the internal capsule and basal ganglia

24. Variant anatomy MCA duplication: reported incidence of ~1.5% (range 0.2-2.9%); parallels the main MCA and supplies the anterior temporal lobe accessory MCA MCA fenestration is rare with a reported incidence of <1% early branching of the MCA-bifurcation/trifurcation occurs within 1 cm of its origin

25. POSTERIOR CEREBRAL ARTERY The  posterior cerebral arteries  are the terminal branches of the basilar artery and supply the occipital lobes and the posteromedial temporal lobes. origin:  terminal branches of the basilar artery course:  from basilar towards occiput main branches Posterior communicating artery (not really a branch, see embryology below) Medial and lateral posterior choroidal arteries Calcarine artery supply:  occipital lobes and posteromedial temporal lobes

26. P1: pre-communicating segment From basilar artery bifurcation to the junction of pcom P2: post-communicating segment Extend from P1 and curves around cerebral peduncle within ambient cistern P3: quadrigeminal segment Extends behind the midbrain to calcarine fissure P4: cortical segment ​within the sulci of the occipital lobe P5: terminal branches terminal branches of the calcarine artery and parieto-occipital artery 

27. Variant anatomy Fetal posterior cerebral artery: unilateral incidence 13-15%, bilateral incidence 0.5%  9 Fenestration: rare Duplicated: rare, fetal origin and normal origin on the same side  6

28. MAGNETIC RESONANCE VENOGRAM MR cerebral venography  ( MRV ) is an MRI examination of the head with either contrast-enhanced or non-contrast sequences to assess patency of the  dural venous sinuses and cerebral veins.  INDICATIONS Suspected cerebral venous thrombosis is the primary indication. Preoperative assessment of anatomy, particularly for posterior fossa surgery, where the sigmoid sinuses may be compressed (e.g. retrosigmoid craniotomies) may also warrant an MRV.  CT venography is a reliable and very rapid alternative exam, however it utilizes ionizing radiation and iodinated contrast media.

29. The veins of the brain drain into the intracranial dural venous sinuses, which eventually drain into the internal jugular veins of the neck. The characteristic features of the venous drainage of the brain are as follows: The venous return in the brain does not follow the arterial pattern. The veins of the brain are extremely thin-walled due to the absence of muscular tissue in their walls. The veins of the brain possess no valves. The veins of the brain run mainly in the subarachnoid space. The veins of the brain comprise cerebral veins, cerebellar veins, and veins of the brainstem.

30. CEREBRAL VEINS The cerebral veins are divided into external (superficial) and internal cerebral veins, which drain the external surfaces and the internal regions of the cerebral hemisphere, respectively. EXTERNAL CEREBRAL VEINS The external cerebral veins drain the surface (cortex) of the hemisphere and are divided into three groups, viz. 1. Superior. 2. Middle. 3. Inferior.

31. SUPERIOR CEREBRAL VEINS The superior cerebral veins are about 8–12 and drain the upper parts of the superolateral and medial surfaces of the cerebral hemisphere. They ascend upwards, pierce the arachnoid mater, and traverse the subdural space to enter the superior sagittal sinus. The anterior veins open at right angles, while the posterior open obliquely against the flow of bloodstream in the superior sagittal sinus, thereby preventing their collapse by increased CSF pressure.

32. MIDDLE CEREBRAL VEINS The middle cerebral veins are four, two on each side: the superficial middle cerebral vein and the deep middle cerebral vein. The superficial middle cerebral vein lies superficially in the lateral sulcus. Anteriorly, it runs forward to drain into the cavernous sinus, while posteriorly, it communicates with the superior sagittal sinus via superior anastomotic vein (of Trolard ) and with the transverse sinus via inferior anastomotic vein (of Labbe). The deep middle cerebral vein lies deep in the lateral sulcus on the insula along with the middle cerebral artery. It runs downwards and forwards and joins the anterior cerebral vein to form the basal vein.

33. INFERIOR CEREBRAL VEINS The inferior cerebral veins are many in number but smaller in size. They drain the inferior surface and lower parts of medial and superolateral surfaces of the cerebral hemisphere into nearby intracranial dural venous sinuses, e.g., transverse sinus.

34. VENOUS DRAINAGE OF DIFFERENT SURFACES OF CEREBRAL HEMISPHERE VENOUS DRAINAGE OF SUPEROLATERAL SURFACE Superolateral surface of the cerebral hemisphere is drained by the following veins: Superior cerebral veins: They drain the upper part into the superior sagittal sinus. Inferior cerebral veins: They drain the lower part into the superficial middle cerebral vein, however some from the posteroinferior part drain into the transverse sinus

35. Venous Drainage of Inferior Surface Inferior surface of the cerebral hemisphere is drained by the inferior cerebral veins: 1. Inferior cerebral veins from the orbital part: They drain into the superficial, middle cerebral, and anterior cerebral veins. 2. Inferior cerebral veins from the tentorial part: They drain into: (a) venous sinuses at the base of skull, viz. cavernous, superior petrosal, straight and transverse sinuses, and (b) superficial middle cerebral vein, which drains into cavernous sinus and basal vein, which drains into the straight sinus.

36. VENOUS DRAINAGE OF MEDIAL SURFACE Medial surface of the cerebral hemisphere is drained by the following veins: 1. Superior cerebral veins: They drain the upper part into superior sagittal sinus. 2. Inferior cerebral veins: They drain the lower part into the inferior sagittal sinus. 3. Some of the veins from the posterior part: These veins drain into the great cerebral vein. 4. Anterior cerebral vein: It drains the anterior part.

37. The superficial veins drain mainly into the superior sagittal sinus, which ultimately drains into the right internal jugular vein. On the other hand, the deep veins drain mainly into the great cerebral vein, which ultimately drains into the left internal jugular vein.

38. DURAL VENOUS SINUSES   Dural venous sinuses  refer to multiple venous channels within the cranial cavity, which are sandwiched between the two layers of the dura mater (the outermost layer of the meninges). This venous system represents the main pathway of returning venous blood from the brain into the circulation via the  internal jugular vein .

39. UNPAIRED SINUSES 1. SUPERIOR SAGITTAL SINUS 2. INFERIOR SAGITTAL SINUS 3. STRAIGHT SINUS 4. OCCIPITAL SINUS 5. INTERCAVERNOUS SINUSES

40. PAIRED SINUSES 1. TRANSVERSE SINUS 2. SIGMOID SINUSES 3. CAVERNOUS SINUSES 4. SUPERIOR PETROSAL SINUSES 5. INFERIOR PETROSAL SINUSES

41. On the left, a T2-weighted image with normal flow void in the right sigmoid sinus and jugular vein (blue arrow). On the left there is abnormal high signal as a result of thrombosis (red arrow).

42. Absence of normal flow void on MR (2) The images on the left show abnormal high signal on the T1-weighted images due to thrombosis. The thrombosis extends from the deep cerebral veins and straight sinus to the transverse and sigmoid sinus on the right. Notice the normal flow void in the left transverse sinus on the right lower image. Absence of normal flow void on MR-images can be very helpful in detecting venous thrombosis

43. Venous infarction The other sign that can help us in making the diagnosis of unsuspected venous thrombosis is venous infarction. Venous thrombosis leads to a high venous pressure, which first results in vasogenic edema in the white matter of the affected area. When the process continues it may lead to infarction and development of cytotoxic edema next to the vasogenic edema. This is unlike in an arterial infarction, in which there is only cytotoxic edema and no vasogenic edema. Due to the high venous pressure, hemorrhage is seen more frequently in venous infarction compared to arterial infarction.

44. Since many veins are midline structures, venous infarcts are often bilateral. This is seen in thrombosis of the superior sagittal sinus, straight sinus and the internal cerebral veins.

45. Venous infarction - Superior sagittal sinus thrombosis The most frequently thrombosed venous structure is the superior sagittal sinus. Infarction is seen in 75% of cases. The abnormalities are parasagittal and frequently bilateral. Hemorrhage is seen in 60% of the cases. On the left, bilateral parasagittal edema and subtle hemorrhage in a patient with thrombosis of the superior sagittal sinus.

46. FLAIR image demonstrating high signal in the left thalamus. When you look closely and you may have to enlarge the image to appreciate this, there is also high signal in the basal ganglia on the right. These bilateral findings should raise the suspicion of deep cerebral venous thrombosis. A sagittal CT reconstruction demonstrates a filling defect in the straight sinus and the vein of Galen (arrows).

47. normal contrast-enhanced MR venography. Notice the prominent vein of Trolard (red arrow) and vein of Labbe (blue arrow).