Principles of Advanced Musculoskeletal Imaging Flashcards
What is a CT scan?
Merges x–ray technology with the computer to provide detailed digital cross-sectional images of the body relatively free from superimposition of the different tissues
How is a CT scan different from x-rays?
CT is based on axial slices- lots of projections at lots of different angles
May have 60+ slices per view
How is a CT scan similar to x-rays?
Uses ionizing radiation
Same gray scale for reading images applies to both CT scans and x-rays
What are the three different types of CT images?
3-D CT
CT myelography
Cone beam CT
How does image processing work in a CT scan?
volume averaging
Averaging of tissues of different radiodensities in a voxel
Results in some loss of contrast resolution
Partially resolved by taking thinner slices
How do you view a patient’s image in a computed tomography (CT)?
Axial image viewed as if patient were supine and examiner is looking from the feet up
Examination requires good understanding of 3-D anatomy
Examiner will scroll through multiple slices per body region
Pathology may only be present on a few slices
What does a CT scan image best?
BONE!!
More specifically
Loose bodies in a joint
Subtle or complex fractures
Degenerative changes
Spinal stenosis
Osseous alignment
Summary overall best at examining geographic changes of the skeleton
What are the advantages of a computed tomography (CT)?
Less expensive than MRI
Less claustrophobia
Can image soft tissue and bony structures in one series
Quicker than MRI
What are the disadvantages/limitations of a CT scan?
Lots of radiation exposure
Volume averaging of radiodensities within a voxel
Different tissues may be assigned the same shade of gray and thus look similar (ex: muscle and tumor)
What is an MRI scan?
Cross-sectional imaging technology that uses the magnetic field and radiofrequency signals to cause hydrogen nuclei to emit their own signals, which then are converted to images by a computer
The energy emitted varies according to the tissues from which the signals emanate
Allows MRI to distinguish between different tissues (esp. soft tissues)
Does NOT use ionizing radiation
What type of MRI view is this?
Coronal
What type of MRI view is this?
Axial
What type of MRI view is this?
Sagittal
The physics of an MRI?
We are made of water hydrogen protons in our water will align with the magnetic field when in an MRI
A radiofrequency pulse knocks protons out of alignment and energy is absorbed in the process
When the RF pulse is turned off, the protons relax and realign and release their absorbed energy this induces a current in the receiver coil that produces electrical data sent to the computer
Each soft tissue has a different amount of water content it will absorb and thus a different rate at which it releases energy
The differences in energy levels produced by different tissues are used to create the image
The computer reconstructs the image based on the sequences that have been chosen
What is an MRI sequence?
refers to the timing of the radiofrequency pulse and the capturing of the energy signal
Which of these images is a T-1 MRI and which one is a T2
The one on the left is T-1
the one on the right is a T2 (cerebral spinal fluid and fluid in intervertebral disc much brighter)
What type of image and plane is this?
Ultrasound, longitudinal
What type of image in plain is this?
Transverse, ultrasound
