AGR324 Exam 4: MRI & Nuclear Medicine

Ch. 13: What does MRI stand for?

Magnetic resonance imaging

What is used to obtain an MRI scan? (think physics)

A magnetic field and radiofrequencies are used to determine the chemical make-up of a substance

Which imaging modality is better to look at soft tissue: CT or MRI?

MRI- Demonstrates the concentration of free-floating hydrogen molecules so has better contrast than CT or radiography

What all can be imaged with MRI?

brain, spinal cord, soft tissue

Can you go in an MRI machine if you have a pacemaker?

NO

What is the most dangerous aspect of an MRI?

the extremely strong magnet- Projectile affect

What is precession?

how much an atom wobbles

What are some naturally occurring magnetic materials?

iron, malachite

How can we create a magnet?

• Can be induced by exposing some metallic objects to a strong magnetic field.

• Can be created by applying an electrical current through copper windings

What units are used to measure magnetic strength?

-Gauss (G): imperial unit of magnetism

-Tesla (T): metric unit of magnetism

Which unit is used to describe medical magnets?

Tesla (T)

What are the 3 types of medical MRI magnets?

• Permanent magnets

-2 slabs of magnetic material facing each other

-<0.3T

——————————————

• Electromagnets (resistive magnets)

-Electrical charge applied through copper wire

-<-.6T

——————————————

• Superconducting magnets

-Most common

-Large electromagnets that are superconductive in very low temperatures

->/= 1T

-Never turned off!

What is used to keep a superconducting magnet active?

Liquid helium used to keep the magnet active

Which of the 3 types of medical magnets is the strongest?

Superconducting magnet

????? What is the MRI room surrounded by and why is this necessary?

Faraday cage- specialized, continuous conductive shielding—typically copper, aluminum, or galvanized steel panels—that encases the entire room, including the walls, floor, and ceiling.

Blocks external radiowaves and contains magnetic field produced by machine

What is the difference in T1 and T2 decay?

T1- direct movement of the center of the atom from its tipped position to its original state

T2- Spinning of the atom back into its original state

What is TR?

(repetition time)

• Time between radio frequency pulses, changes contrast of the images

What is TE?

(echo time)

• Time between responses showing the maximum signal

Instead of radiographic densities, we refer to the different shades of gray in MRI images as __________.

Signal intensities

High signal intensity: bright or closer to white

Low signal intensity: darker shades of gray

What will the CSF vs skin look like in a T1 weighted image?

CSF looks black (low signal intensity), Fat (and skin) look bright/white (high signal intensity)

What with the CSF vs skin look like in a T2 weighted image?

CSF looks bright white, skin looks black

What is the contrast agent used in MRI scans and how is it excreted?

Gadolinium; excreted by kidneys

What do you need to use Gadolinium?

normal kidney function

What is a localizer?

low quality initial image

Do our patients require sedation for an MRI scan?

yes

Ch. 14: What is an isotope?

if the number of neurons differs

What is a radionucleotide?

Radioactivity: atoms that are in abnormally excited states and have an unstable nucleus

What is radioactive disintegration decay?

(Radioactive decay): the atoms are trying to become stable again, so they spontaneously emit particles and energy

What is "half-life" and why does it matter?

how long it takes for the isotope to lose half of it's original radioactivity

With nuclear scans, are looking at area of greater or lesser cellular activity?

greater cellular activity

Do nuclear studies demonstrate function or anatomy?

function

What are looking for with a nuclear scan/why do we do them at all?

• Equine lameness

• Evaluation of fracture healing

• Things that don't "fit" in a CT or MRI machine.

• Patients that "can't" be anesthetized.

What radioisotope do we usually use for nuclear imaging studies?

• Small animals

-Iodide-131: mostly treats hyperthyroidism

-Technetium-99

• Large animals

Technetium-mdp (prefers bone)

What is a hot spot?

is an area of increased cellular activity

What is a gamma photon burst?

emission of radiation; the camera detects gamma photon bursts

What are the 3 phases of a nuclear scan and how long after administration do they each occur?

Vascular phase

• Usually only done if a thrombus is suspected

• Camera detects DURING INJECTION and traces the movement of the radioisotope through the circulation

Soft tissue phase

• ~10 minutes after injection

• Tendons, ligaments, soft tissue structures of the joints

• Large muscle masses are so big they cause "fogging" of the image"

Bone phase

• 2-3 hours after injection

What is the half-life of technetium99?

6 hrs

How long do we keep the animal in the hospital?

48 hrs

What do we do with the animal waste during that time?

retained in a lead-lined container for 48 hours

What do we scan the room and the technician with before and after nuclear studies?

a Geiger counter

What is a PET scan and why do we do it?

Positron Emission Tomography;

Hybrid imaging that combines nuclear medicine with CT OR MRI

• PET scanners detect photons and calculate their origin

• Instead of a single camera being moved around an animal, multiple cameras are mounted in rows on a ring. The table moves through the ring and the cameras take "slice" images.

It's used to image the brain function and look for malignant tumors

What isotope is used in a PET scan?

Fluedoxyglucose (FDG)