67.67_Magnetic Resonance Imaging

By the end of the lesson learners will be able:

10.4.2.4 – to explain the practical importance of magnetic resonance imaging;

Keywords

Magnetic Resonance Imaging (MRI)

What is MRI?
History
Common uses
How it works?
Basic MRI scans
Specializes MRI scans

Diffusion MRI
Magnetic Resonance Angiography
Safety risks
Future
Advantages
Disadvantages

Produces very clear, detailed pictures of the organs and structures in the body
It is a form of medical imaging that uses no Ionizing radiation
MRI makes use of the property of Nuclear magnetic resonance (NMR) to image nuclei of atoms inside the body.

The first MR image was published in 1973
The first studies performed on humans were published in 1977
Created by Dr. Raymond V. Damadian, Dr. Larry Minkoff and Dr. Michael Goldsmith
In 2003, The 2003 Nobel Prize in Physiology or Medicine was awarded to Paul C Lauterbur and Peter Mansfield
Made new MR imaging techniques
Faster and more efficient

Physicians use the MR examination to help diagnose or monitor treatment for conditions such as:
Tumors and other cancer related abnormalities.
Certain types of heart problems.
Blockages or enlargements of blood vessels
Diseases of the liver, such as cirrhosis, and that of other abdominal organs.
Diseases of the small intestine, colon, and rectum

An MRI machine uses a powerful magnetic field to align the magnetization of some atoms in the body.
radio frequency fields systematically alter the alignment of this magnetization
This causes the nuclei to produce a rotating magnetic field detectable by the scanner
This information is recorded to construct an image of the body.

Images are constructed when protons in different tissues return to equilibrium state at different rates.
Five variables effect these rates
Spin Density: Concentration of nuclei in tissue processing in a given region under a magnetic field.
T1: Longitudinal relaxation time
T2: Transverse relaxation time
Flow: Shows blood flow, CSF flow
Spectral Shifts: Angle/zoom the picture is taken from.

T1-weighted: Differentiate fat from water
Water is Darker, fat is brighter
Provide good gray matter/white matter contrast in brain.
T2-weighted: Differentiate fat from water
Fat shows darker, and water lighter.
Good for imaging edema
Abnormal accumulation of fluid beneath the skin or in one or more cavities of the body

Diffusion MRI
Measures diffusion of water through biological tissues.
Diffusion may be anisotropic (unequal physical properties along different axes)
Diffusion Tensor Imaging (DTI)
Examine areas of neural degeneration and demyelination in diseases such as Multiple Sclerosis (MS)

Magnetic resonance angiography (MRA)
Generates pictures of arteries.
Evaluates the arteries of the neck and brain, the thoracic and abdominal aorta, the renal arteries, and the legs
Uses gadolinium injection as paramagnetic contrast agent
Magnetic resonance venography (MRV) is a similar procedure that is used to image veins.

MRI’s create up to 120dB
Equivalent to jet engine at take off.
Contraindications:
Pacemakers, Vagus Nerve Stimulators, implantable defibrillators, insulin pumps, deep brain stimulators
Any electronic or magnetized foreign bodies (surgical prosthesis)
Peripheral nerve stimulation (PNS)
Rapid switching on and off of the magnetic field gradients is capable of causing nerve stimulation

People hold the part of their body being scanned motionless for 30-60 minutes.
Procedure is done in multiple parts.
Takes time to switch between different scans and fields of view.

More detailed images
All MRIs use color?
Better pictures of bone structures
Shift from x-rays and CT scans to MRI
New Scanning sequences

Very safe because no radiation is used
Produces 3-D images
Images can be stored
Produces clear/detailed images

Disadvantages

High cost
Patients with heart implants cannot go for MRI
Not suitable for patients who fear to be confined in a small area
A slight movement by patient can cause image to be blurred ( patient cannot move)
Pregnant women cannot use MRI.