MRI uses strong magnets and radio waves to produce detailed images of the inside of the body without using ionizing radiation. It has important applications in neurology and musculoskeletal imaging. The MRI machine consists of a powerful magnet that aligns hydrogen atoms, gradient coils to vary the magnetic field, and RF coils used to transmit pulses and receive signals. During an MRI scan, the patient lies within the magnet while RF pulses are used to alter the hydrogen atom alignment and produce signals used to create images, with different sequences like T1-weighted and T2-weighted yielding different tissue contrasts.

1. )

2. objectives
 MRI
 Introduction
 equipment components
 procedure
 how it helps in diagnosis

3. Magnetic Resonance Imaging
(MRI)
 Pronounced
 (mag-NET-ik REZ-oh-nans IM-ij-ing)
 Defined
 Noninvasive scanning procedure that provides
visualization of fluid, soft tissue, and bony structures
without the use of radiation

4. INTRODUCTION
 Magnetic resonance imaging (MRI) has its greatest
application in the fields of neuroradiology and
musculoskeletal radiology.
 MRI uses the magnetic properties of spinning
hydrogen atoms to produce images. The first step in
MRI is the application of a strong, external magnetic
field.

5. EQUIPMENT COMPONENTS AND
THEIR PROCEDURE
 For this purpose, the patient is placed within a large powerful magnet.
Most current medical MRI machines have field strengths of 1.5 or 3.0
tesla (1.5T or 3T). The hydrogen atoms within the patient align in a
direction either parallel or antiparallel to the strong external field.
 A greater proportion aligns in the parallel direction known as
longitudinal magnetization.
 A second magnetic field is applied at right angles to the original
external field. This second magnetic field is known as the
radiofrequency pulse (RF pulse)
 A magnetic coil, known as the RF coil, applies the RF pulse. The RF
pulse causes the net magnetization vector of the hydrogen atoms to
turn towards the transverse plane, i.e. a plane at right angles to the
direction of the original, strong external field.

8. EQUIPMENT COMPONENTS
 Each medical MRI machine consists of a number of magnetic coils:
• 1.5T or 3T superconducting magnet
• Gradient coils, contained in the bore of the superconducting magnet,
used to produce variations to the magnetic field that allow image
formation
 RF coils are applied to, or around, the area of interest and are used to
transmit the RF pulse and to receive the RF signal.
 RF coils come in varying shapes and sizes depending on the part of the
body to be examined
 Larger coils are required for imaging the chest and abdomen, whereas
smaller extremity coils are used for small parts such as the wrist or
ankle.

9. PROCEDURE
 To form a magnetic resonance image, the patient is placed in a strong uniform
magnetic field. The magnetic field aligns hydrogen nuclei within the patient in
the direction of the field. The nuclei are “disturbed” from this orientation by
application of an external radiofrequency (RF) pulse. After the RF pulse is
stopped, the hydrogen nuclei return to their alignment within the externally
imposed magnetic field, giving off RF signals as they lose energy.
 In their natural state, hydrogen atoms are spinning with their axes of rotation
randomly oriented. When placed in a magnetic field, they align in a uniform
direction. An RF pulse is applied, knocking the H-atoms out of their magnetic
field orientation. Once the RF pulse is stopped, the atoms return to their
previous alignment, giving off a signal which is then used to form the image.

10. •Each RF signal is analyzed by the computer for its intensity and other criteria.
The signals are then assigned gray-scale values (white to black) on the detector
by the computer.

13. PROCEDURE (cont.)
 There are two basic sequences in MRI that are important to understand
and recognize.
 These sequences are known as the T1-weighted and T2-weighted
sequences. The “weighting” represents the exploitation of specific
properties of hydrogen atoms that are exposed to a magnetic field.
 T1-weighted images classically demonstrate water as hypointense
(dark) and fat as hyperintense (bright), with different soft tissues
expressed as a gradient in between.
 In T2-weighted images water is represented as hyperintense and fat as
hypointense (again with soft tissues in the middle).

14.  Bright signal on T1 spin echo
- Blood
- Fat including Bone marrow
- Protenacious material
- Melanin
- Paramagnetic substances e.g. gadolinium
 Dark signal on T1 spin echo
- Fluid
- Most lesions
- Metallic objects
- Calcification & Air
- Cortical bone
SIGNAL INTENSITY

15.  Bright signals on T2 spin echo
- Subacute blood
- most lesions
- Fluids
- Melanin
 Dark signals on T2 spin echo
- Fat
- Calcification
- Chronic blood (hemosiderin)
- Air

16. THERE ARE THREE TYPES OF MAGNETS:
• Resistive Magnets
• Permanent Magnets
• Superconducting Magnets
Resistive magnets: The resistive magnet has many coils
of wire that wrap around the bore, through which
electrical currents are passed, creating a magnetic field.
This particular magnet requires a large amount of
electricity to run, but are quite cheap to produce

17.  Permanent Magnets: The permanent magnet is one
that delivers a magnetic field, which is always on at full
strength and therefore, does not require electricity.
The cost to run the machine is low due to the constant
magnetic force. However, the major drawback of these
magnets is the weight in relation to the magnetic field
they produce.

18.  Superconducting Magnets: The superconducting
magnets are very similar to the design of the resistive
magnets, in that they too have coils through which
electricity is passed creating a magnetic field
 The superconducting magnet is the most commonly
used in machines today, giving the highest quality
images of all three magnet types