Basics of MRI

BASICS OF MRI and clinical applications

DR SAKHER-ALKHADERICONSULTANT RADIOLOGIST AMC

"Felix Bloch and Edward Purcell, both of whom were awarded the Nobel Prize in 1952, discovered the nuclear magnetic resonance (NMR) phenomenon independently in 1946. In the period between 1950 and 1970, NMR was developed and used for chemical and physical molecular analysis. In 1971 Raymond Damadian showed that the nuclear magnetic relaxation times of tissues and tumors differed, thus motivating scientists to consider magnetic resonance for the detection of diseases. Dr. Damadian and his team spent the next seven years diligently designing and creating the first MRI machine for medical imaging of the human body."

MRI HISTORY

FONAR introduced the world's first commercial MRI (a whole-body MRI scanner) in 1980, and went public in 1981.

The first human scan by Dr Damadian on July ,3,1977

The first MRI images produced by the machine .

1977Modern MRI

TYPES OF MRI

The OPEN MRI's started to come into production . The initial intent was to provide a tool to perform the MRI diagnostic testing for patients that were a) Claustrophobic or 2) Too obese to fit into the Closed models.

Neutral Flexion Dynamic MRI

Surface Coils.Surface coils are designed to provide a very high RF sensitivity over a small region of interest. These coils are often single or multi-turn loops which are placed directly over the anatomy of interest. The size of these coils can be optimized for the specific region of interest.

MRI : WHAT IS THE EXACT PRINCIPLE

RADIOFEQUENCY

TURN OFF

Camera

SO TO GET AN IMAGE WE NEED

THE SIGNAL IS DISPLAYED ON GREY SCALE

AND ACCORDING TO THE RELAXATION TIME WE GET

Dark signal on all sequences

SPECIAL MRI SEQUENCES

DIFFUSION WEIGHTED IMAGING (DWI)

Diffusion weighted imaging (DWI) is a form of MR imaging based upon measuring the random Brownian motion of water molecules within a voxel of tissue. The relationship between histology and diffusion is complex, however generally densely cellular tissues or those with cellular swelling exhibit lower diffusion coefficients, and thus diffusion is particularly useful in tumour characterisation and cerebral ischaemia. 

CLINICAL APPLICATIONS DW imaging has a major role in the following clinical

situations 3-5:  early identification of ischemic stroke differentiation of acute from chronic stroke differentiation of acute stroke from other stroke mimics differentiation of epidermoid cyst from arachnoid cyst differentiation of abscess from necrotic tumors assessment of cortical lesions in CJD differentiation of herpes encephalitis from diffuse temporal

gliomas assessment of the extent of diffuse axonal injury grading of gliomas and meningiomas (need further study) assessment of active demyelination 

EPIDERMOID CYST

CHOLESTEATOMA

BRAIN ABSCESS

MRI PERFUSION

Functional magnetic resonance imaging or functional MRI (fMRI) is a functional neuroimaging procedure using MRItechnology that measures brain activity by detecting associated changes in blood flow.[1][2] This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area of the brain is in use, blood flow to that region also increases.The primary form of fMRI uses the blood-oxygen-level dependent (BOLD) contrast,[3]

 discovered by Seiji Ogawa. This is a type of specialized brain and body scan used to map neural activity in the brain or spinal cord of humans or other animals by imaging the change in blood flow (hemodynamic response) related to energy use by brain cells.

MRI SPECTROSCOPY The basic principle that enables MR spectroscopy (MRS) is the electron cloud around an atom that shields the nucleus from the magnetic field to a greater or lesser degree. This naturally results in slightly resonant frequencies, which in turn return a slightly different signal.

MR spectroscopyMR spectroscopy (MRS)

Hunter's anglelactate peak: resonates at 1.3 ppmlipids peak: resonate at 1.3 ppmalanine peak: resonates at 1.48 ppmN-acetylaspartate (NAA) peak: resonates at 2.0glutamine-glutamate peak: resonate at 2.2-2.4 ppm gamma-aminobutyric acid (GABA) peak: resonate at 2.2-2.4 ppmcitrate peak: resonates at 2.6 ppmcreatine peak: resonates at 3.0 ppmcholine peak: resonates at 3.2 ppmmyo-inositol peak: resonates at 3.5 ppm

MRI TRACTOGRAPHY

MR ELASTROGRAPHY Magnetic resonance elastography (MRE) is a 

non-invasive medical imaging technique that measures the mechanical properties (stiffness) of soft tissues by introducing shear waves and imaging their propagation using MRI. Pathological tissues are often stiffer than the surrounding normal tissue. For instance, malignant breast tumors are much harder than healthy fibro-glandular tissue. This characteristic has been used by physicians for screening and diagnosis of many diseases, through palpation. MRE calculates the mechanical parameter as elicited by palpation, in a non-invasive and objective way.

SUSEPTIBILTY WEIGHTED IMAGES ( SWI) FOR HEMORRHAGE

THE END