Neurotransmitter 2.0 January 2018

Why Use MRI in Neurology?
– by Hannah White, LVT

Welcome to the latest edition of the Neurotransmitter 2.0 Technically Speaking, a publication for technicians written by our technicians.

History

In 1977, this technology was harnessed to produce the first human MRI scan. MRI began being used in clinical practice in the Mid 1980s. MRI was utilized in veterinary medicine primarily as a research tool in the 1980s to early 1990s. (Gavin & Bagley)

Following the change of the millennium, MRI was more widely available. MRI became the modality of choice for veterinary neurologists as it allowed them to get detailed information related to disease processes affecting the brain and spinal cord.

Why Do We Use MRI?

MRI yields the most complete anatomical information and is currently “the gold standard” for evaluating the brain and spinal cord.

MR imaging yields superior images of soft tissue such as spinal cord, intervertebral discs, nerve roots, peripheral nerves in close proximity to spinal cord as well as other paraspinal structures.

So why not CT scans to evaluate central nervous system disease? CT or computed tomography is X-Ray based technology has similar limitations to X-rays: CT has a hard time distinguishing soft tissue versus fluid as well as differentiating between soft tissues. Thus, it cannot tell us integrity of spinal cord or get good images of brain tissue.

The brain is composed of numerous structures of varying water/lipid/protein content. In contrast to CT, MRI has been shown to have superior soft tissue contrast & resolution, thus it easily differentiates between soft tissue and fluid. In addition, it can discern between different soft tissues because of their slightly different compositions.

CT is also limited because it only provides us with images on an axial plane. Unlike CT, MRI allows examination in any imaging plane. We commonly image in 3 planes (see below). Multi-planar imaging is important because it lessens the chance that artifacts could be misinterpreted as lesions, and also makes true lesions less likely to avoid detection.

What about ultrasound? Ultrasound is also not practical as it is difficult to penetrate skull and bone.

MRI gives us vibrant, very detailed pictures of the area of interest, plus there is no radiation!

How Does MRI Work?

mri2.jpg
  • A strong magnetic field is created by passing an electric current through metal loops.
  • Coils in the magnet start to send and receive radio waves.
  • Protons in the body begin to align themselves, and once this occurs the radio waves are absorbed by those protons. Then they begin to spin.
  • The energy that is released from these spinning protons emits a signal which varies based on the type of tissue they reside in.
  • The signals are received by magnetic coils and sent to computer for processing.
  • The processing computer then produces a “voxel” image by interpreting the radio waves received, which is what we end up seeing in an MRI image.

 

Patient Monitoring

Our canine and feline patients must undergo anesthesia, so an anesthesia machine and MRI compatible monitoring is placed on the patient and is viewed on a monitor in the MRI control room by the anesthesia technician.

Below is a picture of one of BAVI’s MRI suites and control room.

 

 

 

 

 

 

 

 

 

 

 

MRI is Interactive

Multiple sequences allow for views of:

  • Anatomy
  • Pathology
  • Blood flow
  • Flow of CSF

These sequences combined allow the neurologist to determine a diagnosis.

3 Planes of Imaging Used in MRI

SAGITTAL AXIAL CORONAL (DORSAL)
SAGITTAL VIEW is a side to side view. This is a single 4 mm “slice” of the center of this canine’s brain AXIAL VIEW is an end on view looking from the tip of the nose towards back of the head. This is a single 3.5 mm “slice” of the center of this canine’s brain CORONAL OR DORSAL VIEW is a view from the top of the patients head looking down. This is a single 3.5 mm “slice” in this orientation at the level of the eyes

References

Posh, John ( 2016). Veterinary MRI with John Posh RT(R)(MR). American Association of Veterinary Radiologists Lessons 1, 7, 8, 13. Class Lecture slides. Retrieved from ce.aavr.org
Gavin, Patrick R. and Bagley, Rodney S. (2009) Practical small animal MRI. Iowa: Wiley-Blackwell.

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