PET/MRI & SPECT/MRI

Why the development of PET/MRI and SPECT/MRI was slower compared to PET/CT or SPECT/CT?

due to the immense magnetic field that nuclear medicine equipment felt from the MRI magnet

What happens when the integration of MRI into nuclear medicine SPECT system?

some of the detector elements would fail and not be able to produce a measurable response from radiation emitted due to the electromagnetic field from the magnet

Why PET/MRI scanners are not affected?

due to their detectors being on opposite sides of the machine and with proper shielding of the magnetic field

What does Magnetic Resonance Imaging utilizes?

through the use of a magnetic field collecting valuable soft tissue information from the body

Long Bore Scanners

Which is your traditional close tube (this is the one that gives patients claustrophobia)

Short Bore Scanners

This is the scanner that was modified to be 50% shorter and 5% wider to accommodate large pts & pts with claustrophobia

What is the most optimum bore scanner?

long bore scanner provides better spatial resolution. Note: Both of these can be used.

How is the magnetic field of strength is measured?

In Tesla and Gauss. 1T=10,000 G

Permanent Magnets

are always on, they do not require the use of electrical currents to maintain their magnetic fields. These magnets also have vertical fields generally less than 0.3 T

Resistive Magnets

depend on electrical currents to generate their magnetic fields. They typically have limited, or low field strengths of 0.6 T

Superconductive Magnets

Use cryogens to control their temperatures. Electrical currents flow without any resistance through superconducting wires immersed in the cryogens. These are the most commonly used magnet in MRI with a magnet strength of 0.5 - 7 T.

What is the Earth’s magnetic pull?

50 uT to 0.5 Gauss

What does an MRI is surrounded by?

by a very strong INVISIBLE magnetic field, which has the potential to attract ferrous metal.

What does the MRI also have the ability to?

interfere with the normal operation of electronic devices.

What is DEADLY IMPORTANT for a single MRI technologist to do when interacting with patients?

gets a very detailed history from each patient who is screened before an MRI.

What happens if a MRI tech failed to identify patient history?

Failure to identify a Pacemaker, Neural Implants, Bullet fragments, Stroke Clips and other various metallic devices could lead to bodily harm or death if not caught before scanning.

What is the 5 Gauss line?

the point at which a magnetic field becomes dangerous. A magnetic object can become a projectile past this point.

What is the advantage of MRI of over other modalities?

it can acquire images in any desired plane instead of just a single plane, It can display the three conventional planes: Axial, Coronal & Sagittal also the operator may also generate oblique or in between plane views for acquisition of specific organs.

What was MR originally termed?

Nuclear Medicine Resonance or NMR

What was the origin of MRI?

when Nikola Tesla discovered rotating magnetic fields in 1882

Who discovered NMR of radio-waves in a magnetic field?

Isidor Rabi, 1930s

Who developed an instrument that could measure the magnetic resonance in bulk material such as liquids and solids?

Felix Bloch & Edward Purcell in 1946

What Felix Bloch & Edward discovered?

certain nuclei were placed in a magnetic field they absorbed energy in the radiofrequency range of the electromagnetic spectrum, and re-emitted this energy when the nuclei returned to their original state.

When Felix Bloch & Edward Purcell won the Nobel Prize for physics?

1952

Who discovered the strength of the magnetic field and the RF pulse matched one another?

Sir Joseph Larmor

What was the relationship called when Sir Joseph Larmor discovered the strength of the magnetic field and the RF pulse?

Larmor Frequency

What did Sir Peter Mansfield demonstrate?

in the 1970’s how to mathematically analyze MR signals and convert them into images. Sir Mansfield also demonstrated echo planar imaging

What did Peter Lauterbur discover?

Discovered how to create 2D images by introducing gradients into the magnetic field

What did Raymond Damadian build?

the first NMR scanner in 1997 after acquiring the patent in 1972. His machine was named the Indomitable

What did Richard Ernest receive?

the nobel peace prize in 1991 for his work on HiRes pulsed Fourier transformation spectroscopy

What did Kurt Wuthrich receive?

the 2002 Nobel peace prize for demonstrating 3D molecular structures in a solution.

Nuclear

Is due to the nuclei of specific elements and atom reacting to magnetic field

Magnetic

A magnetic field is required

Resonance

The direct frequency dependence of the magnetic and RF Fields

What is the MRI examination for?

is a diagnostic procedure in which strong magnetic fields, radio-waves and a computer are used to acquire images of the bodies anterior.

What are the images of the MRI and is it Ionizing radiation?

images are multidimensional and are not produced using ionizing radiation, any area of the body may be scanned

What is the important to remember when working with MRI?

It is important to remember that when working around a superconducting magnet that the magnetic field is always on.

What is the first step of the MR examination?

1. Place the body part to be examined in the center of the MRI scanner bore

What is the second step for an MR examination?

2. While the patient is in the scanner, they need to be exposed to the strong magnetic field, when this happens the hydrogen nuclei in the body align with the magnetic field.

What is the 3rd step of an MR examination?

3. Radiofrequency pulses are then used to flip the hydrogen atoms out of alignment with the magnetic field.

What is the fourth step of an MR examination?

4. The RF pulse is stopped, so the nuclei realign with the magnetic field causing transverse magnetization

What is the 5th step of an MR examination?

5. When the hydrogens (relax) realign in the body there is a readable signal from the tissue that can be converted into data and then an image.

What does the loud thumbing indicate?

you hear during MRI examinations is the pulses being turned on/off.

How does the T1 relaxation or the Longitudinal or spin-lattice is measured?

when the net magnetization pulse is turned off and the hydrogen begin to respond to the pull of the main magnetic field.

What happens when T1 relaxation time is a time constant?

that becomes steadily greater in size after the RF energy is turned off. This is set to be the amount of time to reach 63% longitudinal magnetization of the original magnetization of the base magnet

What differs for a longitudinal magnetization recovers?

for various tissues and is the fundamental contrast in T1 images based on Magnetic field strength

How the T2 relaxation or Transverse or Spin Spin is measured?

This is measured when a pulse is emitted than is exposed to a 90 degree pulse that rotates the magnetization into the transverse plane. After which the protons begin to dephase due to spin spin relaxation processes.

What happens to T2 in the transverse plane begins to decay?

When a 37% loss in magnetization has occured this is the T2 time.

What are T1 and T2 relaxations are?

time concepts that characterize rates of magnetic relaxation. The T1 & T2 relaxation processes occur simultaneously.

What happens after the applications of a 90-degree RF pulse?

the transverse magnetization (T2 decay) dephases, while the longitudinal magnetization rephases (T1) parallel to the static field.

What happens during the relaxation process?

the spins shed the excess energy acquired from the 90 degree RF pulse in the form of RF waves.

How do we produce an MR image?

the RF waves are captured. The RF waves can be gathered using a receiver coil.

What is the coils purpose?

The coil can stand alone or be combined with a transmitter coil for a transmit/reciever coil. Coils are specialized for individual parts of the body

Pixel Area

Field of View / Matrix ; This is in reference to a 2D image

Voxel Volume

(Field of View/Matrix) x slice thickness

Voxel Size regarding CT

Volume = Pixel pitch / Geometric Magnification

What is Geometric Magnification?

is the ratio of the focus-detector distance (FDD) and the focus -object distance (FOD)