• uses magnetic field for cross sectional imaging of the body

• superconducting magnet - source of the external, static magnetic field
• coils - used for transmission of radio frequency pulses and for reception of weak signals produced by the tissues

• body is subjected during the examination to:
  external, static magnetic field ( ,2 - 1,5 T, modern generation 3 T)
  gradient magnati field
  radio frequency waves
  sound waves
  _ magnetic fields and waves are not harmful, risks are associated with ferromagnetic objects in body

• absolute: pacemaker, intracranial ferromagnetic aneurysm clips, metallic orbital foreign body, electrodes in the heart, defibrillators, cochlear implants, catheters, neurostimulators.
• relative: claustrophobia, non - controlled motions, 1st trimester pregnancy

• Ad: non-invasive, no ionising radiation, multiplaner, high contrast and septal resolution, high sensitivity, assess haemorrhage ( detect the product of haemoglobin's degradation), MR angio non-invasive of blood vessels ( blood works as contrast), MR hydrography for spaces and tracts containing fluids: MR cholangiography, MR urography, MR myelograqphy

• Dis: long time, no motion during the examination, need sedation / anaesthesia - small children, uncooperative pats., high cost, low availability, sensitivity for artefacts, low sensitivity in detection calcification ( except special grading sequence).

• source of MRI.
• RF pulses cause excitation of the protons

• T1 -longitudinal relaxation time - time of regeneration of longitudinal magnetization. Fluid is hypointense (dark) and fat is hyperintense (bright).
• T2-transvere relaxation time - time of decay of transverse magnetization Fluid is hyperintense (bright) and fat is hypointense (dark) water is “white” on T2 as “World War II”

• hyperintense = high (bright) signal
• isointense = similar signal.
• hypo intense = low (dark) signal
  compared to neighbouring tissues

• intensity depends on: proton density, T1 relaxation time, T2 relaxation time, contrast enhancement
• most of pathologies appear as hypo or isointense on T1 and hyper intense on T2

• fat and extracellular methemoglobin hyper-intense on T1 and T2
• hemosiderin, calcification, fibrous tissue hypo-intense on T1 and T2
• inracellular methemoglobin, melanin hyper on T1 and hypo on T2
• most of tumors, inflammation, ischemia, demyelination, edema, fluid, cysts hypo on T1 and hyper on T2

• paramagnetic properties.
• commonly used agents: magnevist, omniscan, prohance ( contain chelated gadolinium)

congenital anomalies, disease of white matter (demyelinating, inflammation), neoplasms (primary and metastases), postoperative changes, affects of radio/chemotherapy, reoccurrence of tumor, ischemic lesions, hydrocephalus, assessment of cranial nn., vascular pathology, post-traumatic, post-inflammatory changes, assessment of banister and medulla

• cavernoma: consist of dilated, blood - filled sinusoids, present heterogeneous signal
• venous angioma: small venous channels that drain into a larger vein
• dany-walker syndrome: dilated 4th ventricle is connected with cyst of the posterior fossa + cerebellar vermin hypo-alisa
• demyelinating foci are located in: periventricular area, corpus collusum, brainstem ( FLAIR - most sensitive sequence)

• criteria of the assessment of the tumors:
  localisation (intra/extraaxial, supra/infratentorial), size, intensity, structure (solid, cyst, mixed, necrotic), degree of contrast enhancement, borders, mass effect

• Gliomas -
  the most common intraaxial tumor
  types: Astrocytoma, Glioblastoma multiforme, Oligodendroglioma, Ependymoma, chroid plexus papilloma (intense), medulloblastoma

• most common extra axial .
• connected with flax, dura, tentorium.
• causes displacement of adjacent tissues
• common in F
• well circumscribed, hypo intense on T2WI, homogenous contrast enhancement
• calcification (CT)

• intense enhancement.
• located in pinto-cerebellar angle, internal acoustic canal (n.VII, VIII), prepotine cistern (n.V)
• well-circumscribed

eremitic reaction, mass effect, ring -like pattern of enhancement