MRI basics - How to read and understand MRI sequences

Described the basics, physiology, sequences on how to identify and clinical significance of MRI in stroke

1. Various MRI Sequences How to identify and its Clinical significance Co-Ordinator: Dr.U.Meenakshisundaram Presenter: Dr.M.Ramesh Babu Apollo Main Hospital SYMPOSIUM ON NEURO IMAGING

2. MRI - an imaging modality that uses non-ionising radiation to create useful diagnostic images. MRI pulse sequence - a programmed set of changing magnetic gradients. Number of parameters: TE, TR, flip angle, diffusion weighting Multiple sequences are grouped together into an MRI protocol. Different combinations of these parameters affect tissue contrast and spatial resolution. NMR - discovered just after the end of the Second World War. INTRODUCTION

3. MRI Principle MRI is based on the principle of nuclear magnetic resonance (NMR) Two basic principles of NM Atoms with an odd number of protons or neutrons have spin A moving electric charge, be it positive or negative, produces a magnetic field Body has many such atoms that can act as good MR nuclei (1H,13C, 19F, 23Na) Hydrogen nuclei is one of them which is not only positively charged, but also has magnetic spin MRI utilizes this magnetic spin property of protons of hydrogen to elicit images

4. MRI- the use of NMR to produce 2D images in 1976. Human images a year later in 1977 MRI scanner : consists of Powerful magnet in which the patient lies. Radio wave antenna - to send signals to the body and then receive signals back. These returning signals are converted into images by a computer attached to the scanner . Imaging of any part of the body can be obtained in any plane.

5. TR & TE TR (repetition time) : the time between two excitations is called repetition time TE (echo time) : time interval in which signals are measured after RF e xcitation In general short TR (<1000ms) and short TE (<45 ms) scan is T1W Long TR (>2000ms) and long TE (>45 ms) scan is T2 W Long TR (>2000ms) and short TE (<45 ms) scan is Proton density

6. Why MRI? No ionising radiation Image aquisition in multiple planes Superior soft tissue contrast Some angiographic images can be obtained without the use of contrast material Advanced techniques such as diffusion, spectroscopy and perfusion allow for precise tissue characterisation rather than merely 'macroscopic' imaging Functional MRI allows visualisation of both active parts of the brain during certain activities and understanding of the underlying networks Risk of iodinated contrast allergy alleviated

7. Disadvantages More expensive Not easily available Longer scan time Patient comfort can be an issue - Noisy , Claustrophobia Subject to unique artefacts Not safe patients with some metal implants , pacemaker and foreign bodies MR contrast posses risk

8. Anatomy

9. Descriptive Terminology H igh signal intensity/ hyperintense = W hite I ntermediate signal intensity/ isointense = G rey L ow signal intensity/ hypointense = B lack

10. Variety of Sequences T1WI T2WI POST GD FLAIR STIR DW1/ADC GRE/SWI PDWI MRS MRA MRV CSF FLOW STUDY MR PERFUSION DTI PET

11. T1 & T2 W I MAG I NG

12. GRADATION OF INTENSITY I M A GING C T S C A N C S F Ed ema White M a t ter Gray Ma t ter B l ood B o n e MRI T1 C S F Ed ema Gray M a t ter White Ma t ter Cart i l a g e F a t MRI T2 C a r t i l a ge Fat White M a t ter Gray Ma t ter Ed ema C S F MRI T2 Flair C S F C a r t i l a g e Fat White Ma t ter Gray M a tt e r E d ema

13. CT SCAN MRI T1 Weighted MRI T2 Weighted MRI T2 Flair

14. Dark On T1 Edema Tumor Infection Inflammation Hemorrhage( hyperacute, chronic) Low proton density, Calcification Flow void

15. Bright On T1 Fat Subacute Hemorrhage Melanin Protein rich fluid Slowly flowing blood Paramagnetic substances (gadolinium,copper,manganese)

16. Basic Neuro Sequences Four Shades of Gray – T1 No protons / excited protons Air Dense Calcification/ Cortical Bone Fluid (CSF) (Protein) Brain Tissue GM WM Fat Ga d o l i n i u m Methemoglobin Black Dark Intermediate White

17. Bright On T2 Edema Tumor Infection Inflammation Subdural collection Methemoglobin in late subacute hemorrhage

18. Dark On T2 Low proton density Calcification Fibrous tissue Paramagnetic substances(deoxy hemoglobin,methemoglobin(intracellular),ferritin,hemosiderin,melanin. Protein rich fluid Flow void

19. Basic Neuro Sequences Four Shades of Gray – T2 No protons/ exacted ptotons Air Dense calcification Flow voids (Protein B o und water tissues WM GM Brain Tissue Free water Fat Oxyhemoglobin Black Dark Intermediate White

20. Which Scan Best Defines the Abnormality T1 W Images: Subacute Hemorrhage, Fat-containing structures, Anatomical Details T2 W Images: Edema, Demyelination, Infarction, Chronic Hemorrhage FLAIR Images: Edema, Demyelination, Infarction esp. in Periventricular location

21. FLAIR & STIR

22. Conventional Inversion Recovery Two important clinical implementations of the inversion recovery concept are: Short Time to inversion-recovery ( STIR ) sequence Fluid-attenuated inversion-recovery ( FLAIR ) sequence.

23. Short Time to Invertion Recovery STIR It is transverse magnetization that induces an electric current in the receiver coil so no signal is generated from fat. STIR sequences provide excellent depiction of bone marrow edema which may be the only indication of an occult fracture. Unlike conventional fat-saturation sequences STIR sequences are not affected by magnetic field inhomogeneities, so they are more efficient for nulling the signal from fat

24. FLAIR First described in 1992 and has become one of the corner stones of brain MR imaging protocols. A sequence with a long TR and TE and an inversion time (TI) that is tailored to null the signal from CSF In contrast to real image reconstruction, negative signals are recorded as positive s ignals of the same strength so that the nulled tissue remains dark and all other tissues have higher signal intensities .

25. Most pathologic processes show increased SI on T2-WI, and the conspicuity of lesions that are located close to interfaces b/w brain parenchyma and CSF FLAIR images are heavily T2-weighted with CSF signal suppression , highlights hyperintense lesions and improves their conspicuity and detection, especially when located adjacent to CSF containing spaces

26. Basic Neuro Seq Four Shades of Gray – F that isn't free uences LAIR M M Bl a ck Free water Dark Interme d i a te Br ai n T i ss u e W G White T2 bright tissue w a t e r .

27. Clinical Implications It is u sed to evaluate diseases affecting the brain parenchyma neighboring the CSF - containing spaces for eg: MS & other demyelinating disorders. Unfortunately, less sensitive for lesions involving the brainstem & cerebellum, owing to CSF pulsation artifacts Helpful in evaluation of neonates with perinatal HIE . Useful in evaluation of gliomatosis cerebri owing to its superior delineation of neoplastic spread Useful for differentiating extra-axial masses eg. epidermoid cysts from arachnoid cysts. However, distinction is more easier & reliable with DWI.

28. Mesial temporal sclerosis : m/c pathology in pts. with partial complex seizures.Thin-section coronal FLAIR is the standard sequence in these patients & seen as a bright small hippocampus on dark background of suppressed CSF containing spaces. However, normally also mesial temporal lobes have mildly increased SI on FLAIR images. Focal cortical dysplasia of Taylor’s balloon cell type - markedly hyperintense funnel- shaped subcortical zone tapering toward the lateral ventricle is the characteristic FLAIR imaging finding In Tuberous Sclerosis- detection of hamartomatous lesions , is easier with FLAIR than with PD or T2-W sequences

29. Embolic infarcts- Improved visualization Chronic infarctions- typically dark with a rim of high signal . Bright peripheral zone corresponds to gliosis, which is well seen on FLAIR and may be used to distinguish old lacunar infarcts from dilated perivascular spaces.

30. Subarachnoid Hemorrhage (SAH): FLAIR imaging surpasses even CT in the detection of traumatic supratentorial SAH. It has been proposed that MR imaging with FLAIR, gradient-echo T2*-weighted, and rapid high-spatial resolution MR angiography could be used to evaluate patients with suspected acute SAH, possibly obviating the need for CT and intra-arterial angiography. With the availability of high-quality CT angiography, this approach may not be necessary.

31. DWI & ADC

32. DWI Diffusion-weighted MRI is a example of endogenous contrast, using the motion of protons to produce signal changes. DWI images is obtained by applying pairs of opposing and balanced magnetic field gradients (but of differing durations and amplitudes) around a spin-echo refocusing pulse of a T2 weighted sequence. Stationary water molecules are unaffected by the paired gradients, and thus retain their signal. Nonstationary water molecules acquire phase information from the first gradient, but are not rephased by the second gradient, leading to an overall loss of the MR signal.

33. The normal motion of water molecules within living tissues is random (brownian motion). In acute stroke, there is an alteration of homeostasis. Acute stroke causes excess intracellular water accumulation , or cytotoxic edema, with an overall decreased rate of water molecular diffusion within the affected tissue. Reduction of extracellular space - Tissues with a higher rate of diffusion undergo a greater loss of signal in a given period of time than do tissues with a lower diffusion rate. Therefore, areas of cytotoxic edema, in which the motion of water molecules is restricted, appear brighter on diffusion-weighted images because of lesser signal losses. Restriction of DWI is not specific for stroke

34. Di f f u si o n Weighted Imaging Non fluid-restricted tissue Fluid-restricted tissue (maybe) Black Dark Intermediate White

35. AD C Apparent Diffusion Coefficient – ADC MAP A measure of magnitude of diffusion True Fluid Restriction Not Fluid Restriction (T2 Shine Through) Black Dark Intermediate White

36. D e sc r i p t i o n T1 T2 FLAIR DWI ADC White m at t er High Low I n t e r m e d i a t e Low Low Grey m at t er I n t e r m e d i at e I nte r m e d i a t e high I n t e r m e d i at e I nte r m e d i a t e CSF Low High low low High

37. The primary application of DW MR imaging has been in brain imaging, mainly because of its exquisite sensitivity to early detection of ischemic stroke. The increased sensitivity of diffusion-weighted MRI in detecting acute ischemia is thought to be the result of the water shift intracellularly restricting motion of water protons (cytotoxic edema), whereas the conventional T2 weighted images show signal alteration mostly as a result of vasogenic edema .

38. Core of infarct = irreversible damage Surrounding ischemic area ◊ may be salvaged Regions of high mobility “rapid diffusion” ◊ dark Regions of low mobility “slow diffusion” ◊ bright Difficulty : DWI is highly sensitive to all of types of motion (blood flow, pulsatility, patient motion).

39. DWI useful in Diagnosing Ischemic Stroke Extra axial masses: arachnoid cyst versus epidermoid tumor, Intracranial Infections Pyogenic infection, Herpes encephalitis, Creutzfeldt-Jakob disease Trauma Demyelination

40. Apparent Diffusion Coefficient It is a measure of diffusion Calculated by acquiring two or more images with a different gradient duration and amplitude (b-values) To differentiate T2 shine through effects or artifacts from real ischemic lesions. The lower ADC measurements seen with early ischemia , An ADC map shows parametric images containing the apparent diffusion coefficients of diffusion weighted images. Also called diffusion map

41. ADC The ADC may be useful for estimating the lesion age and distinguishing acute from subacute DWI lesions . Acute ischemic lesions can be divided into hyperacute lesions (low ADC and DWI-positive ) Chronic lesions can be differentiated from acute lesions by normalization of ADC and DWI . A tumour would exhibit more restricted apparent diffusion compared with a cyst because intact cellular membranes in a tumour would hinder the free movement of water molecules

42. Non Ischemic Causes For Decreased ADC Abscess Lymphoma and other tumors Multiple sclerosis Seizures Metabolic (Canavans )

43. DW MRI characteristics of Various Disease Entities MR Signal Intensity

44. Disease DW Image ADC Image ADC Cause Acute Stroke High Low Restricted Cytotoxic edema Chronic Strokes Variable High Elevated Gliosis Hypertensive e n c e p ha l o pa t h y Variable High Elevated Vasogenic edema Arachnoid cyst Low High Elevated Free water Epidermoid mass High Low Restricted Cellular tumor Herpes encephalitis High Low Restricted Cytotoxic edema CJD High Low Restricted Cytotoxic edema MS acute lesions Variable High Elevated Vasogenic edema Chronic lesions Variable High Elevated Gliosis

45. Clinical Uses of DWI & ADC STROKE: Hyperacute Stage :- within one hour minimal hyperintensity seen in DWI and ADC value decrease 30% or more below normal (Usually <50X10-4 mm2/sec) Acute Stage :- Hyperintensity in DWI and ADC value low but after 5- 7days of ictus ADC values increase and return to normal value (Pseudonormalization) Subacute to Chronic Stage :- ADC value are increased (Vasogenic edema) but hyperintensity still seen on DWI (T2 shine effect)

46. GR E

47. Gradriant Recalled Echo GRE This feature of GRE sequences is exploited- in detection of hemorrhage , as the iron in Hb becomes magnetized locally (produces its own local magnetic field) and thus dephases the spinning nuclei. The technique is particularly helpful for diagnosing hemorrhagic contusions such as those in the brain and in pigmented villonodular synovitis. SE sequences, on the other hand- relatively immune from magnetic susceptibility artifacts, and also less sensitive in depicting hemorrhage and calcification.

48. Flair GRE Hemorrhaoge in Rt. Parietal Lobe

49. Gradiant Echo Prons : Fast Technique Cons : More sensitivity to magnetic susceptibility artefacts Clinical Use: Eg: Haemorrhage or Calcification

50. GRE SWI

51. Susceptibility Weighted Imaging SWI is a very sensitive type of gradient echo MR sequence. SWI is for the identification of small amounts of hemorrhage /blood product or calcium, both of which may be inapparent on other MR sequences. Compounds that have paramagnetic, diamagnetic, and ferromagnetic properties all interact with the local magnetic field and result in loss of signal. SWI is more sensitive than GRE for cerebral microbleeds.

52. Axial FLAIR ( A ), T2-weighted ( B ), and SWI ( C ) images show a large hematoma in the left frontal lobe ( asterisks ). A few small hemorrhages with surrounding edema were also visible in the right subcortical white matter ( open arrows ) on the FLAIR and T2-weighted images. There is also a small right convexity subdural collection with hemorrhage ( arrows ). However, numerous additional hemorrhagic foci throughout the bilateral hemispheric white matter are only visible on SWI

53. MRA & MRV MRA Time-of-flight ( TOF ) imaging is most commonly used for MRA. Signal in intracranial arteries is related to flow phenomenon , and thus no IV gadolinium is needed. TOF MRA can be performed by both 2D and 3D techniques. Contrast-enhanced MRA is often used to evaluate the neck vasculature. Contrast-enhanced intracranial MRA is useful in patients with stent and/or coils. MRV can be performed with 2D /3D TOF techniques, which do not need administration of IV gadolinium. Contrast-enhanced MRV is, however, more robust and is less susceptible to artifacts compared with the TOF techniques.

54. In 2DFT technique , multiple thin sections of body are studied individually and even slow flow is identified In 3DFT technique , a large volume of tissue is studied ,which can be subsequently partitioned into individual slices, hence high resolution can be obtained and flow artifacts are minimised , and less likely to be affected by loops and tortusity of vessels MOTSA (multiple overlapping thin slab acquisition): prevents proton saturation across the slab. This technique have advantage of both 2D and 3D studies. It is better than 3D TOF MRA in correctly identifying vascular loops and tortusity, and have lesser chances of overestimating carotid stenosis.

55. MR Perfusion MR Perfusion Perfusion MR (with contrast) can be performed using 2 major techniques : Dynamic susceptibility contrast MR perfusion ( DSC ) and dynamic contrast-enhanced perfusion ( DCE ). DSC perfusion gives information on relative CBV, relative CBF, MTT, and TTP, useful in stroke patients. DCE perfusion examines the leakiness of blood vessels to generate permeability maps. Both DSC and DCE techniques can be used in evaluation of brain tumors . Arterial spin labeling ( ASL ) is an MR perfusion method for quantitatively measuring CBF by taking advantage of arterial water as a freely diffusible tracer. ASL is completely noninvasive, repeatable, and is performed without gadolinium.

56. Digital Subtraction Angiography (DSA) DSA is still considered the " gold standard " in vascular imaging. However, DSA is an invasive procedure associated with risk of complications, 1% overall incidence of neurologic deficit and 0.5% incidence of persistent deficit. Diagnostic indications for DSA include assessing for aneurysms in subarachnoid hemorrhage when CTA/MR are negative, accurate assessment of arteriovenous malformations , and intracerebral hemorrhage of unknown etiology.

57. MRS

58. MR Spectroscopy Means of noninvasive physiologic imaging of the brain that measures relative levels of various tissue metabolites. Wide clinical application

59. OBSERVABLE METABOLITES M e ta b o l i t e Loca t i o n N o r m a l f u n c t i o n I n cr e as e d ppm L i p i ds 0.9 & 1.3 Cell membrane component Hypoxia, trauma, high grade neoplasia. Lactate 1.3 TE=272 (u p r i g h t ) TE=136 ( i n verte d ) Denote s a n a e r o b i c glycolysis Hypoxia, stroke, necrosis, mitochondrial diseases, neoplasia, seizure A l a n i n e 1.5 A m i n o a c i d Meningioma Acetate 1.9 Anabolic p re c urs or Abscess , N eop l a s i a ,

60. PRI CI P L E M E T ABOL TES Metabolite L o c a t i on ppm Normal fu n c ti o n Increased D ecr e as e d NA A 2 Nonspecific neuronal marker (Reference for chemical shift) C ana v an ’ s disease Neuronal loss, stroke, dementia, AD, hypoxia, neoplasia, abscess Glutamate , glutamine, GABA 2.1- 2.4 N e u rotrans m i t ter Hypoxia, HE Hy p ona t r e m i a S u c c i n a t e 2.4 P ar t of T C A cycle Bra i n abs ces s C r e a t i n e 3 . 03 Cell energy marker (Reference for metabolite ratio) Trauma, h y p ero s m o l a r state Stroke, hypoxia, neoplasia

61. M e t a b o l it e Loca t i o n ppm Normal fu n c t i on I n cr e as e d D ecr ease d C h o l i n e 3.2 Marker of c ell membrane turnover Neoplasia, d emy e l i n a t i o n (MS) Hypomyelination Myoinositol 3.5 & 4 As t r ocy te marker AD Dem y el i n a t i n g diseases

62. Metabolite Ratio Normal abnormal NAA/ Cr 2.0 <1.6 NAA/ Cho 1.6 <1.2 Cho/Cr 1.2 >1.5 Cho/NAA 0.8 >0.9 Myo/NAA 0.5 >0.8

63. M R S Dec. NAA/Cr Inc. acetate, succinate, amino acid, lactate Neuodegene r a t i ve A l z h e i me r D e c.. NAA/Cr Dec NAA/ C h o Inc. M y o/ N A A Slightly inc. Cho/ Cr Cho/NAA Normal Myo/NAA ± lipid/lactate Inc. Cho/Cr Myo/NAA Cho/NAA Dec. NAA/Cr ± lipid/lactate M a l i g n a n cy D e m y e l i n a t i n g disease P y o g e n i c abscess

64. Lactate :Lactate is generally seen as a doublet (two peaks close together) at a frequency of 1.33 ppm. Healthy tissue does not have sufficient lactate to be detectable with MRS. Lactate , as a product of anaerobic glycolysis, is detected in diseased brain when oxygen starved. It is of great diagnostic value in cases of hypoxia , brain injury, and stroke. It is also elevated in some tumors where it is suggestive of aggressiveness as well as abscesses .

65. N- Acetyl Aspartate : At 2.0 ppm, NAA is an amino-acid derivative synthesized in neurons and transported along axons.  It is therefore a " marker" of viable neurons, axons, and dendrites. The diagnostic value of NAA lies in the ability to quantify neuronal injury or loss on a regional basis and therefore, decreased NAA plays a diagnostic role in brain tumors, head injury, dementias, and many other neurological disorders in which neuronal loss is expected.  Increased NAA is observed only in recovery and in Canavan disease that is due to a specific genetic disorder that reduces NAA-deacyclase activity resulting in net accumulation of NAA.

66. Glutamate—Glutamine—Gamma-amino Butyrate (Glx) : A mixture of closely related amino acids, amines and derivatives involved in excitatory neurotransmission lie between 2.1 and 2.4ppm. Glx is a vital marker(s) in MRS of stroke, lymphoma, hypoxia , and many metabolic brain disorders.

67. Creatinine Cr : The primary resonance of creatine lies at 3.0ppm. It is the central energy marker of both neurons and astrocytes and remains relatively constant. For that reason, it is often used as an internal reference for comparison to other metabolites. While some studies have found Cr reduced, it is only in inborn errors of metabolism that significant reductions of Cr occur.

68. Choline: Choline includes several soluble components of brain myelin and fluid-cell membranes that resonate at 3.2ppm. Because by far the majority of choline-containing brain constituents are not normally soluble, pathological alterations in membrane turnover (tumor, leukodystrophy, multiple sclerosis) result in a massive increase in MRS-visible Cho.

69. Myo- Inositol ml : A little known polyol (sugar-like molecules) that resonates at 3.6ppm mI is mostly a diagnostic “modifier” in those diseases that affect Cho ( tumor, MS , etc). As an astrocyte marker and osmolyte, mI contributes specificity in dementia diagnoses , and an almost absolute specificity to hepatic encephalopathy and hyponatremic brain syndromes.

70. Clinical Application MRS MRS of brain masses: Distinguish neoplastic from non neoplastic masses Primary from metastatic masses Tumor recurrence vs radiation necrosis Prognostication of the disease Mark region for stereotactic biopsy Monitoring response to treatment

71. Diffusion Tensor Imaging DTI is an interesting application of diffusion imaging , which assesses diffusion in at least 6 different directions and yields a more complete diffusivity information compared with standard DWI. This information can be used to deduce axonal fiber orientation and create 3D color-encoded maps of white matter tracts in the brain. Red indicates right to left, green encodes anterior to posterior, and blue denotes superior to inferior tract orientation

72. Clinical application Assess the deformation of white matter by tumours - deviation, infiltration, destruction of white matter Delineate the anatomy of immature brains Pre-surgical planning Alzheimer disease  - detection of early disease Multiple Sclerosis- plaque assessment

73. fMRI fMRI is a technique used to obtain functional information by visualizing cortical activity . fMRI detects subtle alteration in blood flow in response to stimuli or actions. It is used in clinical practice typically for presurgical mapping of eloquent areas (e.g., speech and motor skills) and in research aimed at elucidating novel neural networks.

74. Positron Emission Tomography PET involves injection of a radioactive tracer ( isotope, such as 11C, 18F, and 15O ). PET enables in vivo examination of brain functions and quantification of CBF, metabolism, and receptor binding. PET tracers used to study neurological disorders include 18F- 2-deoxyglucose (F-18 FDG) for glucose metabolism, 11C- raclopride for dopamine D2 receptors, 11C-methionine for cellular amino acid uptake, and 11C-flumazenil for central benzodiazepine binding. 18F-6-fluorodopa ( 18F-dopa ) is 1 of the most commonly used ligands for studying the dopaminergic system in movement disorders . Differentiating various types of parkinsonian syndromes clinically, especially in the early stages of the disease, can be difficult, and PET may be employed as an adjunct to clinical diagnosis in equivocal cases.

75. Main clinical use of PET in epilepsy is localization of epileptogenic foci in potential surgical candidates with partial seizures. F-18 FDG PET can provide important prognostic information , as increased glucose metabolism of gliomas correlates with higher histological grades (III and IV) and shorter survival period. Similarly, increased uptake of 11C-methionine , which reflects cellular amino acid uptake, is indicative of high-grade glioma and poorer survival. F-18 FDG PET has been used extensively to study dementia, and it may be an effective tool for early diagnosis and differentiation of various types of dementia. Amyloid PET imaging using 11C-Pittsburg compound (PiB) and 18F-AV-45 (florbetapir) have high sensitivity in detecting amyloid plaques.

76. MRI Protocols Combination of multiple sequences- to adequately evaluate a tissue - MRI protocol . The radiologist tailors the pulse sequences to try to best answer the clinical question posed by referring physician. The implementation of a protocols has 3 chief purposes : -maximising diagnostic quality -delivery of consistency in scan quality -efficient and effective radiology service delivery

77. Standard Protocol T1W: saggital purpose: anatomical overview, which includes the soft tissues below the base of skull T2W:axial purpose: evaluation of basal cisterns, ventricular system and subdural spaces, and good visualisation of flow voids in vessels

78. FLAIR:axial - purpose: assessment of white-matter disorders (e.g. chronic small vessel disease and demyelination diseases) DWI:axial - purpose: multiple possible purposes (from the identification of ischemic stroke to the assessment of active demyelination SWI OR T2*:axial - purpose: identify blood products or calcification

79. Stroke Protocol CT -till the choice as the first imaging modality in acute stroke Availability and the easy and fast access to a CT scanner Better sensitivity for intracerebral haemorrhage ( ICH ) diagnosis . Some institutions -a quick MRI stroke protocol for code stroke patients assessment within the narrow time window for thrombolytic therapy.

80. Stroke Protocol MRI T1W axial - purpose: an anatomical evaluation. Cortical laminar necrosis or pseudolaminar necrosis may be seen as a ribbon of intrinsic high T1 signal, usually after 2 weeks (although it can be seen earlier) T2W axial - purpose: loss of normal signal void in large arteries may be visible immediately after 6-12 hours infarcted tissue becomes high signal sulcal effacement and mass effect develop and become maximal in the first few days

81. FLAIR axial - purpose: after 6-12 hours infarcted tissue becomes high signal sulcal effacement and mass effect develop and become maximal in the first few days DWI / ADC: axial - purpose: early identification of ischemic stroke: diffusion restriction may be seen within minutes following the onset of ischaemia correlates well with infarct core differentiation of acute from chronic stroke SWI/T2 :axial - purpose: highly sensitive in the detection of haemorrhage MRA

82. Non Focal Epilepsy Protocol A good protocol for this purpose involves at least: T1 sequence:   axial and coronal ; in modern scanners it can be replaced by a 3D isotropic acquisition  FLAIR sequence:   axial and angled coronal ; in modern scanners it can be replaced by a 3D isotropic acquisition  Inversion recovery sequences   DWI/ADC SWI  or  T2

83. Temporal Lobe Epilepsy Protocol T1W1 : axial and coronal T2W: angled coronal FLAIR: axial and angled coronal DWI/ADC: axial SWI or T2* : axial

84. Neuro Radiology Ordering Guidelines Indications Preferred study Headache CT head without contrast for acute (“worst headache of life”). MRI without contrast Trauma CT head without contrast (acute). Contusion/TBI: MRI without and with contrast with DTI Suspected intracranial hemor r hage CT head without contrast Acute neurological changes CT head without contrast (only if concern for ICH) Subsequent study: MRI with and without contrast

85. Acute stroke/TIA CT head without contrast (if candidate for thrombolysis) Subsequent studies: MRI brain with /without contrast ( with MR perfusion), MRA brain and MRA neck without and with contrast as indicated Hydrocephalus If concern for shunt malfunction CT head without contrast. Alternative for more acute processes: MRI with and without contrast Seizure First (New Onset) seizures: MRI Brain with and without contrast (CT Head if patient unstable / concern for ICH). Temporal lobe epilepsy MRI without and with contrast with hippocampal volumes. Brain SPECT as needed Dementia / Memory loss MRI brain with & without contrast (Hippocampal volumetrics (Alzheimer’s disease), perfusion, aqueductal stroke volume measurement (NPH)). PET can also be considered for Alzheimer’s diagnosis