mri midterms Flashcards
- Used to visualize the internal structures of the body in high detail.
- It relies on strong magnetic fields and radio waves to produce images of organs and tissues without using ionizing radiation
- Valuable for imaging soft tissues like the brain, spinal cord, muscles, and organs.
Magnetic Resonance Imaging
- primarily used to visualize the anatomical structures of the body, particularly the brain, spinal cord, and joints.
- uses different tissue properties (such as water content) to generate detailed images of soft tissues. Commonly used in diagnosing diseases such as brain tumors, stroke, or spinal cord injuries.
Structural MRI (Anatomical MRI)
Produces high-resolution images that are useful for anatomical details. Fat appears bright, while fluid appears dark.
T1-Weighted Imaging (T1WI)
Sensitive to fluid and is often used to detect pathology.
Fluid appears bright, making it useful for identifying edema or tumors.
T2-Weighted Imaging (T2WI)
- Measures and maps brain activity by detecting changes in blood flow, based on the principle that brain areas with higher activity require more oxygen.
- Tracks changes in blood oxygen levels (BOLD – Blood Oxygen Level
Dependent). Areas of the brain that are active will show changes in oxygenation, which is detected by the MRI scanner. - Studying brain functions like movement, speech, and memory, as well as in research for neurological conditions like epilepsy and Alzheimer’s.
functional MRI (fMRI)
- Assesses the movement of water molecules within tissues, often used for imaging white matter tracts in the brain.
- Measures the diffusion of water molecules, which is more directional in certain tissues like white matter. This technique can visualize the orientation and integrity of white matter pathways.
- Used in neurological conditions such as multiple sclerosis, traumatic brain injury, and stroke. It also helps in planning surgeries for brain tumors to avoid critical areas.
Diffusion MRI (Diffusion Tensor Imaging, DTI)
- A non-invasive technique used to visualize blood vessels.
- Can be performed with or without contrast agents to visualize the blood vessels in the brain, neck, and other parts of the body. It helps assess conditions like aneurysms, blockages, or arterial malformations.
Magnetic Resonance Angiography
Used to visualize arteries without needing a contrast agent.
Time-of-Flight (TOF)
Uses a contrast agent to enhance the visualization of blood vessels, particularly veins and smaller vessels.
Contrast-enhanced MRA
- Measures the chemical composition of tissues, giving insights into the metabolic changes in the body.
- Measures the concentration of metabolites within tissues (e.g., choline, creatine, N-acetylaspartate) by detecting the resonance frequencies of different nuclei (such as hydrogen or phosphorus).
- Used to study brain tumors, epilepsy, and other conditions to identify metabolic changes in tissues.
Magnetic Resonance Spectroscopy
- Specializes in imaging the heart and blood vessels
- Uses MRI to assess the structure and function of the heart, including the myocardium, blood vessels, and heart valves.
- Used for diagnosing heart conditions like cardiomyopathy, myocardial infarction (heart attack), congenital heart defects, and valve disorders.
Cardiac MRI
- Used for imaging the gastrointestinal tract, especially the small intestine.
- Involves the use of an oral contrast agent to highlight the intestines, along with MRI to capture detailed images.
- Used in conditions like Crohn’s disease, inflammatory bowel disease (IBD), and to evaluate bowel obstructions or other pathologies.
MR Enterogtraphy
The MRI machine generates a strong magnetic field. This magnetic field aligns the hydrogen nuclei in the body along the direction of the field.
Magnetic Field Application
A short RF pulse is then applied, which temporarily disrupts the alignment of the hydrogen nuclei. Once the RF pulse is turned off, the hydrogen nuclei begin to return to their original alignment.
Radiofrequency (RF) Pulse
As the hydrogen nuclei relax back into their aligned state, they emit energy in the form of RF signals. The MRI machine detects these signals, which vary based on the type of tissue and the local environment of the hydrogen nuclei
Signal Emission
signals received by the MRI scanner are processed by a computer to construct detailed images. These images are then displayed for interpretation by a radiologist or physician.
Image Reconstruction
strong magnet is the core of the MRI system, generating the primary magnetic field.
Magnet
These coils create varying magnetic fields, allowing for spatial encoding of the MRI signals. This enables the creation of detailed, cross-sectional images.
Gradient Coils
These coils transmit the RF pulses and receive the signals emitted by the hydrogen nuclei as they relax
RF Coils
computer controls the sequence of pulses, processes the raw signal data, and reconstructs it into images.
Computer System
- The magnet is the heart of the MR system
MAGNET
made of wire- wrapped cylinders of I-m diameter and greater, where the magnetic field is produced by an electric current in the wires. The main magnetic field of air core magnets runs parallel to the long axis of the cylinder. Typically, the magnetic field is horizontal and runs along the cranial-caudal axis of the patient lying supine
Air core magnets
constructed from permanent magnets, a wire wrapped iron core “electromagnet,” or a hybrid combination. the magnetic field runs between the poles of the magnet, most often in a vertical direction
Solid core magnets
MRI machines generally use one of three main types of magnet designs:
- Resistive Electromagnets
- Permanent Magnets
- Superconductive Magnets
- constructed in either an air core or solid core configuration.
- systems use continuous electric power to produce the magnetic field produce a significant amount of heat, and often require additional cooling subsystems.
- magnetic field of resistive systems ranges from 0.1 T to about 0.3 T. An advantage of a purely resistive system is the ability to turn off the magnetic field in an emergency.
- disadvantages include high electricity costs and relatively poor uniformity/homogeneity of the field.
Resistive Magnet
- Rely on the ferromagnetic properties of iron, nickel, cobalt, and alloys.
- Operational costs of these systems are the lowest of all MR systems (no major electric or cooling requirements).
- Field uniformity is typically less than a superconducting magnet with similar FOY.
- inability to turn off the field in an emergency is a drawback.
Permanent Magnet
- typically use an air core electromagnet configuration , and consist of a large cylinder of approximately 1 m in diameter and 2 to 3 m in depth, wrapped with a long, continuous strand of superconducting wire.
- Superconductive magnets achieve high field strengths (0.3- to 3.0-T clinical systems are common, and 4.0- to 7.0-T clinical large bore magnets are used in research). In addition, high field uniformity of 1 ppm in a 40-cm3 volume is typical.
Superconductive Magnets
is a characteristic of certain metals that exhibit no resistance to electric current when kept at extremely low temperatures.
Superconductivity
-Very high voltages are used
-Wire winded on coil & electrically applied the ends
-More voltage greater the field
MRI Magnet
- Heavyweight
- Full strength
- Low cost
- Internal core is made of it that generates magnet field all the time
- Rotor Coils Commutator
Permanent magnet
- Internal x-axis is controlled by a resistive magnet
- A portion of imaging is controlled
- Direction around an iron core
Resistive magnet
