SPECIAL SEQUENCES OF MRI

SPECIAL SEQUENCES OF MRI

FLAIR : Fluid attenuated inversion Recovery sequence

(Flair = T2 minus water)

It’s a type of T2 weight MRI where the water is suppressed to make pathology more visible.  It is predominantly used at places where water is the confounding factor and limiting the contrast  eg: Brain

Uses :

. For better appreciation of pathologies in brain being white

.To differentiate arachnoids’ cyst from epidermoid cyst

STIR (Short Tau Inversion Recovery Sequence)

STIR  can be easily remembered as T2- Fat means pathology will remain white whereas Fat will become black.

     It is predominantly used at places where fat is the confounding factor and limiting the contrast, e.g. rest of the body and musculoskeletal imaging

Uses

. Identification of bone marrow edema in diseases like stress fracture ,  avascular  necrosis,  perthes  disease .

.For better appreciation of disease in body where presence of Fat is reducing the contrast due  to background whiteness.

Contrast Enhanced MRI (CEMRI)

Gadolinium containing compounds are most commonly used contrast agents in MRI.

     Presence of gadolinium causes reduction in both T1 and T2 relaxation time which leads to increases in signal on T1- weighted MRI and decreases in signal on T2 weighted MRI. As human eyes appreciate white color better,post contrast MRI images are always acquired as T1-weighted MRI.

MRCP

MRCP images are heavily T2- weighted sequences which demonstrate fluid-filled structures as areas of every high signal intensity and are very commonly used to show the biliary and pancreatic ducts in magnetic resonance cholangiopancreatography(mrcp),being non-invasive and no need of external contrast,it is considered as a preferred investigation to diagnose pathologies of biliary duct and pancreatic duct in comparison to diagnostic endoscopic retrograde cholangiopancreatogrphy (ERCP)

MR Angiography

Visualization of vessels using MRI

   This technique is unique due to the fact that the beautiful angiographic images can be obtained without external administration of contrast. Technique used in MRI for angiography is called TOF(TIME OF FLIGHT).it is a very commonly used angiographic technique now days and is the preferred imaging technique to assess renal artery stenosis and an intracerebral aneurysm.it is also preferred investigation to look for carotid artery stenosis

Diffusion Weighted MRI(DWI)

It is a special type of  MRI technique which assesses the random motion of the water molecule, which is a normal phenomenon. In some disease, there is reduction in the Brownian motion of  the water molecule, which is called as restricted diffusion. Area of restricted diffusion are seen as white on DWI

Common causes of Restricted Diffusion

. Acute ischemic infarct

.Abscess

.High cellular tumors

.Epidermoid cyst

Gradient Echo Imges

Used to see calcification and hemorrhage on MRI which show blooming on gradient images

Spectroscopy

It is a new technique of MRI to assess    certain metabolites in the body tissues. Metabolic changes occur earlier than the structural changes and since routine MRI picks up structure changes, new techniques have been developed for the early diagnosis of the diseases.Commonly studied metabolites are

. N acetyl aspirate

.choline

.creatine

. lipid peak

MRI is Usually a Preferred Investigation for

. For all brain tumors (contrast enhanced MRI)

.For extent of pancoast tumor

.ventricular fuction

.Posterior mediastinal mass

. Bony metastasis in spine

.Chronic subarachnoid hemorrhage 

.Traumatic paraplegia

.Extent of pott’s spine

.Stress fracture,  Perthe’s  disease. avascular necrosis, early osteomyelitis

.Pregnancy after first trimester

.Spinal cord pathologies

.Gynecological malignancies

.Uterine abnormalities