MAGNETIC RESONANCE IMAGING DR. DALIA AL – FALAKI College of medicine Department of radiology

objectives 1-Demonstrate the basic principles of MRI. 2-Identify the congenital anomaly of the brain. 3-Dignose cerebral ischaemic disease. 4-Demonstrate intracerebral bleeding. 5-Dignose white matter disease of the brain.

MAGNETIC RESONANCE IMAGING MRI:employs radiowaves & magnetic fields. - The patient is placed in a magnet & radiowave sent in, the transmitters is turned of & the patient re-emits radiowaves , which are received & used for reconstruction of the image.

MAGNETIC RESONANCE IMAGING WHAT IS THE TYPE OF NUCLEI WHICH ABSORB & emit the radiofrequency energy? It is the nuclei of hydrogen atoms in water & fat which absorb & emit the radiofrequency energy.

WHAT IS THE MAGNETIC FIELD STRENGTH ? The magnetic field strength has a set value between 0.15-2.0 tesla (T), depending on the machine. e.g.1T = this is some 20 000 times greater than the earth's magnetic field.

TISSUE CONTRAST -The MR image maps two properties (T1 ,T2 ) of tissue & is controlled by two parameters set by the operator TE (time to echo) & TR (time to repeat ).

T1 WEIGHTED IMAGE ( LONGITUDINAL RELAXATION TIME) T1 WEIGHTED IMAGE ( LONGITUDINAL RELAXATION TIME): T1 is produced by a short TR , a short TE . +the shorter T1 , the stronger the signal & the brighter the pixel. + fat is white in color as is fatty bone marrow , white matter of the brain & fluid as cerebrospinal fluid is black gray in color .

T2 WEIGHTED IMAGE ( TRANSVERCE RELAXATION TIME) T2 WEIGHTED IMAGE ( TRANSVERCE RELAXATION TIME): T2 is produced by a longer TE , a long TR. +the long T2 , the stronger the signal & the brighter the pixel , water , vitreous cavity of the globes& csf appear white in color while fatty tissue as white matter of the brain appear black gray in color .

T1 WEIGHTED IMAGE

T 2 WEIGHTED IMAGE

T 2/ FLAIR SEQUENCE: fluid attenuation inversion recovery

T 1w + GADOLINEUM INJECTION / SAGITAL SECTION

Sagital section of brain ( T1 w post contrast injection)

CORONAL SECTION OF BRAIN ( T1w post contrast injection)

CONGENITAL LESION OF BRAIN Congenital lesion of brain are well seen by MRI & CT scan but MRI has the advantage of absence of ionizing radiation so can be used safely in children.

Congenital hydrocephalus: Congenital hydrocephalus: Congenital hydrocephalus in infant & young children can be classified as communicating & non – communicating.

Communicating Congenital hydrocephalus : 1-free communication between ventricles & basal cisterns. 2- obstruction to flow of csf is in the subarachnoid space or basal cisterns. 3- this is due to meningeal irritation by hemorrhage ,infection or trauma . 4- all ventricles are enlarged & basal cisterns may be prominent.

NON- Communicating Congenital hydrocephalus : CSF flow is obstructed within the ventricular system , usually at 3rd ventricle , aqueduct or 4th ventricular level. The ventricles are dilated above the level of obstruction.

AQUIDUCT STENOSIS: AQUIDUCT STENOSIS: It is the most common cause of NON- Communicating Congenital hydrocephalus , it is congenital obstruction or stenosis of the aqueduct which result in hydrocephalus involving the 3rd & lateral ventricles.

ARNOLD CHIARI MALFORMATION 1-Donward herniation of cerebellar vermis & medulla oblongata beneath level of foramen magnum. 2- elongation of 4th ventricle. 3- associated with aqueduct stenosis. 4- associated with myelomeningocele.

ARNOLD CHIARI MALFORMATION

ARNOLD CHIARI MALFORMATION

ARACHNOID CYST : ARACHNOID CYST : -clear csf filled cyst. - occur due to congenital splitting of the arachnoid membrane. - they are intracranial but extracerebral. -cam be seen in middle ,posterior cranial fossa , suprasellar region & behind the 3rd ventricle. - they can be large enough to produce mass effect or obstructive hydrocephalus. - there may be Hypoplasia of underlying cerebral tissue such as the temporal pole.

ARACHNOID CYST Coronal T1-weighted MRI image through a brain lesion showing homogeneity of the lesion, lack of a perceptible wall, lack of internal complexity, and CSF signal intensity. There is associated remodeling of the adjacent calvarium and brain displacement. These imaging features are typical of an arachnoid cyst.

ARACHNOID CYST Sagittal fluid-attenuated inversion recovery (FLAIR) weighted image through a brain lesion), showing homogeneity of the lesion, lack of a perceptible wall, lack of internal complexity, and CSF signal intensity. There is associated brain displacement. These imaging features are typical of an arachnoid cyst.

ARACHNOID CYST Axial T2-weighted MRI image through the midbrain, showing a right middle cranial fossa homogeneous lesion) with CSF signal intensity and no perceptible wall or internal complexity. There is associated remodeling of the adjacent sphenoid bone and brain displacement..

Ischaemic infarction 1-focal area of high signal intensity on T2, T2-FLAIR sequences involve vascular territory(left middle cerebral artery). 2-involve the affected gray , white matter. 3- associated with mild mass effect, which manifest itself by obliteration of sulci. 4- in chronic stage ,this ischaemic infarct area change into cerebrospinal fluid filled space which known as aquired porencephalic cyst. 5- ischaemic infarction occure due to occlusion of the arterial supply of brain by atherosclerotic plaques.

Intracerebral bleeding 1- intracerebral bleeding can occur due to trauma, hypertension, haemmorrahic tumor. 2-location deep in the white matter. 3-associated with vasogenic edema arround the bleeding area. 4- bleeding area appear as high signal intensity area on T1w sequence. 5- bleeding area appear low signal intensity lesion on T2w on early subacute stage. 6-bleeding area then appear high signal intensity lesion on late subacute stage. 7-in chronic stage it will change into aquired porencephalic cyst.

WHITE MATTER DISORDER: White matter disease have been classified as: 1-dysmyelinating: there is abnormal formation or maintenance of myelin e.g. leukodystrophies , metabolic disorders. 2-demylinating: there is destruction of normally formed myelin e.g. multiple sclerosis.

MULTIPLE SCLEROSIS: -common neurological disorder. -characterized by disseminated plaques of demyelination & gliosis throughout the neuraxis. -the sites of election are: 1.periventricular. 2.optic pathways. 3.brainstem. 4.cerebellar white matter & peduncles. 5.spinal cord.

MULTIPLE SCLEROSIS: -young adults are primarily affected. -MRI is more sensitive than CT in the demonstration of MS plaques. - the most characteristic appearance is that of periventricular nodular Hyperintense lesions on T2 weighted images. -which are most numerous posteriorly. -the plaques are also well seen at the gray- white matter interfaces.

MULTIPLE SCLEROSIS: -MRI can even image lesions in the spinal cord , brainstem & cerebellum. -multiple cerebral lesions are seen in over half the patient presenting with a single episode of optic neuritis. -some lesion may show a central area of greater signal intensity , resembling a target.

MULTIPLE SCLEROSIS: -contrast enhancement after giving gadolinium occurs in the acute phase indicating activity & in the chronic phase doesn't enhance. -differential diagnosis :1-ischaemic lesions ,2-following radiotherapy ,3- in encephalomyelitis.

MULTIPLE SCLEROSIS:

M.S SAGITAL FLUID ATTENUATION INVERSION RECOVERY SEQUENCE: OVOID PLAQUES ( HIGH SIGNAL INTENSITY) , WHICH ARE PERPENDICULAR TO LATERAL VENTRICLE.