Advances in neuro-imaging
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Recent Modalities of Neuro-imaging discusses various imaging techniques used to image the brain and spinal cord, including: - Computed tomography perfusion which uses contrast to generate maps of cerebral blood flow, volume, and transit time to identify ischemic tissue. - Myelography which uses intrathecal contrast for spinal imaging. - Magnetic resonance techniques like quantitative MRI, diffusion tensor imaging, and MR spectroscopy which provide microstructural data on tissues. - Perfusion imaging uses ultrasound contrast to assess cerebral blood flow. Imaging findings are discussed for conditions like multiple sclerosis, epilepsy, and stroke.
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Advances in neuro-imaging
- 1. Recent Modalities of Neuro-imaging Osama A. Ragab Neurology M.D
- 4. Computed tomography CT -Myelography CT –perfusion
- 6. Perfusion computed tomography allows rapid qualitative and quantitative evaluation of cerebral perfusion by generating maps of cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT). The theoretical basis for PCT imaging is the central volume principle, which relates cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT) as follows: CBF = CBV/MTT. CT –perfusion
- 7. PCT scans are obtained using a 64-slice CT scanner. 40 millileters of a nonionic contrast agent (300 mg of iodine per ml) is injected and flushed by 25 ml of saline at a rate of 5 ml/s, using a standard power injector. Do not wait for the results of creatinine testing, except in case of known history of renal failure or prior serum creatinine measurement that exceeded 1.5 mg/dl, known renal disease, solitary kidney . CT –perfusion
- 8. PCT provides a timely and easy means of identifying ischemic penumbra, permitting rapid triage of patients who may benefit from reperfusion. Distinction between infarct and penumbra from PCT data is based on the concept of cerebral vascular autoregulation. Within the infarct core, autoregulation is lost, and both MTT and CBV are low; within the penumbra, autoregulation is preserved, MTT is increased, but CBV is preserved or even increased. CT –perfusion- Indication
- 10. PCT is used in combination with CTA to monitor cerebral perfusion in SAH patients with a positive Doppler study. MTT maps are reviewed for arterial territories with prolonged MTT values. Such a territory is considered at risk for vasospasm, and the artery supplying this territory is then evaluated by CTA for vasospasm. CT –perfusion- In vasospasm
- 11. CT –perfusion
- 13. Myelography is the technique of instilling intrathecal contrast media for the imaging evaluation of the spinal canal and its contents for all spinal pathology. CT -Myelography
- 14. Cervical nerve root avulsion in brachial plexus injury CT -Myelography
- 15. spontaneous intracranial hypotension CT -Myelography
- 17. Magnetic Resonance Quantitative MRI Proton density Magnetisation Transfer Diffusion tensor image MR spectroscopy
- 18. Magnetic Resonance Quantitative MRI Proton density
- 19. Proton density (PD) measurements indicate the amount of magnetic resonance (MR)-visible protons contributing to the MRI signal. In the brain, PD is used to quantify water content (WC). Proton density
- 20. WC map acquired on an MS patient. The red circle and arrow mark the largest lesion in all images Proton density WC map acquired on a patient with recurrent glioblastoma. The red circle and arrow mark the tumour
- 22. Magnetization transfer (MT) MR imaging is an approach to explore non-water components in tissue. MTI is a structural imaging modality that measures the integrity of white matter tracks, which cannot be easily visualized using conventional MRI. Magnetisation Transfer
- 23. MT MR imaging has been successfully used to describe the severity of tissue damage in MS lesions . It has been observed that MTR drops dramatically when MS lesions start to enhance and that it can show partial or even complete recovery in the subsequent 1 to 6 months. This dynamic is thought to result primarily from de- and remyelination. Hence, MT changes are frequently seen as an ideal means of monitoring this important pathologic process in MS. Magnetisation Transfer
- 24. In a young female patient with RRMS, a | T2-FLAIR MRI reveals macroscopic acute (thick arrow) and chronic (thin arrows) MS lesions with high sensitivity; however, b | postcontrast T1-weighted images are needed to identify the ring-enhancement that is typical of acute lesions owing to the breakdown of the blood– brain barrier. c | Microstructural tissue changes can be quantified with MTI, which shows a reduction of the magnetization transfer ratio at the site of the active lesion. Note the different appearance of the lesion on each of these three maps Magnetisation Transfer
- 25. Magnetic Resonance Quantitative MRI MR spectroscopy
- 26. Peaks lactate: resonates at 1.3 ppm N-acetylaspartate (NAA): resonates at 2.0 ppm glutamine/glutamate: resonates at 2.2-2.4 ppm GABA: resonates at 2.2-2.4 ppm creatine: resonates at 3.0 ppm choline: resonates at 3.2 ppm myo-inositol: resonates at 3.5 ppm NB: ppm = parts per million MR spectroscopy
- 27. The NAA resonance is widely regarded as a marker for neuronal injury and death. A majority of pathologic conditions and diseases demonstrate reduced NAA. A leukodystrophy in which NAA is elevated is Canavan disease. Choline is regarded as a product of myelin breakdown. Increased Cho levels observed in tumors arise from increased cellular density and proliferation of membrane phospholipids The appearance of lactate is pathologic because it classically represents anaerobic glycolysis. Creatine indicate increased metabolic activities. MR spectroscopy
- 28. Gliomas As the grade increases, NAA and creatine decrease and choline, lipids and lactate increase. In the setting of gliomas, choline will be elevated beyond the margins of contrast enhancement in keeping with cellular infiltration. MR spectroscopy
- 29. Ischaemia and infarction Lactate will increase as the brain switches to anaerobic metabolism. When infarction takes place then lipids are released and peaks appear. MR spectroscopy
- 30. multiple sclerosis Acute MS lesions, abnormalities include reduced NAA, increased Cho, and presence of lipids. MR spectroscopy
- 31. Magnetic Resonance Quantitative MRI Diffusion tensor image
- 32. Diffusion ?!!!
- 33. In cerebrospinal fluid, the diffusion of protons is unrestricted in all directions, and therefore isotropic, In highly organized biological tissue, diffusion often is restricted in some directions or anisotropic. and represented by an elongated ellipsoid tensor Diffusion tensor image
- 34. The most commonly used measure for diffusion anisotropy is fractional anisotropy (FA), which gives a normalized value to the tensor's degree of anisotropy (0 is completely isotropic and 1 is completely anisotropic). Diffusion tensors are commonly visualized with color encoded FA maps, which display fiber orientation with three standard colors: red (transverse), blue (craniocaudal), and green (anteroposterior). Diffusion tensor image
- 35. One of the most commonly used algorithms for tractography is known as fiber assignment by continuous tracking (also known as deterministic tractography). probabilistic algorithms allow for the modeling of uncertainty of two (or more) fiber directions at each voxel. Diffusion tensor image
- 36. Brain Tumors presurgical planning and intraoperative guidance in regions adjacent to functional tracts. Diffusion tensor image
- 37. Spinal Cord It is often difficult to differentiate a spinal cord ependymoma from an astrocytoma on conventional MRI. However, the use of fiber tractography has proven to be useful because it often shows displacement of fibers around ependymomas and infiltration of fibers in astrocytomas Diffusion tensor image
- 38. Multiple Sclerosis MS lesions typically demonstrate increased MD and decreased FA compared with contralateral normal appearing white matter . The greatest MD values and lowest FA values are seen in lesions that are hypointense on T1WI, which represent chronic destructive changes where diffusion is least restricted Diffusion tensor image
- 39. Stroke A potential application for DTI in early stroke is using directionally encoded color anisotropy images and fiber tractography to delineate the location of functionally important white matter pathways in relation to the acute infarct. Diffusion tensor image
- 42. This technique allows the detection of ultrasound contrast in the cerebral microcirculation . The intensity of the echo response signal is directly related to the contrast agent concentration in the tissue; therefore, the blood flow assessment is based on monitoring the intensity of the echo response signal of the insonated volume . Brain perfusion imaging
- 45. Reduced deep GM volume, particularly thalamic atrophy, was detected in children with MS compared with a control group, using voxel-based morphometry to assess the pattern of GM loss. Brain Volumetry
- 46. Several sequences have been shown to improve identification of cortical lesions in adult MS patients. Double inversion recovery (DIR) sequence, phase-sensitive inversion recovery, 3D spoiled gradient-recalled echo, and 3D magnetization- prepared rapid gradient-echo. Cortical Imaging Techniques
- 49. The myelin water fraction (MWF) describes the ratio of the myelin water component to total water. MWF was found to be decreased in early MS and to be lower in the progressive compared with the relapsing disease phase Myelin water fraction imaging
- 51. Epilepsy
- 52. This technique compares the myelin concentration of the subject with an age-matched control database and highlights differences. These differences are then presented visually for examination and can be used to focus attention on the cortical area of interest. Myelin Maps
- 53. small transmantle dysplasia was identified in the left superior frontal gyrus (a, arrow) and McDESPOT imaging demonstrated a focal area of decreased myelin concentration in the same area (b, arrow) along with more diffuse myelin loss in the deeper white matter tracts.
- 54. Stroke
- 55. This imaging protocol includes MRA and multicontrast MRI sequences that suppress the signal from adjacent tissue and blood to highlight VW pathologies of both intracranial and extracranial vessels . Vessel Wall MRI
- 57. A 41-year-old woman with morbid obesity, hypertension, and untreated diabetes with a hemoglobin A1c of 8.5% presented with multiple enhancing brain lesions that also showed diffusion restriction (A– C, arrows) and were initially thought to represent demyelination. The lesion in the right brainstem and cerebellum increased in size over 2 weeks (D, arrow). The largest rightmcerebellum and brainstem lesion showed enhancement with contrast administration (E and F, arrows). Computed tomography angiography was initially thought to be negative for any vascular pathology, but no right posterior inferior cerebellar artery (PICA) was detected (G). A cerebellar lesion specimen was subsequently obtained for biopsy, and pathological analysis revealed an infarct. Vessel wall T2-weighted MR images demonstrated an occluded right PICA (H, horizontal arrow) and an eccentric T2-hyperintense plaque (slanted arrow) in the V4 segment proximal to the PICA occlusion. Precontrast (I) and postcontrast (J) DANTE T1 SPACE images demonstrate V4 segment VW enhancement (arrow) indicating actively inflamed plaque.