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
What are the two general sequences in an MRI?
T1 weighted
T2 weighted
Were the benefits of a T-1 sequence?
defines anatomy
Excellent resolution
One of the benefits of a T2 sequence?
makes water brighter
T2 = H2O
Helps to ID pathology (inflammation)
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)
Were the variations of MRIs?
MRI with contrast
MR arthrography
MR myelography
What is an MRI with contrast?
MRI in which is a contrast fluid is injected into the veins of the patient
What is an MRI arthrography?
MRI in which a contrast fluid is injected into the joint
What is an MRI myelography?
Specially sequenced MRI made to highlight the vertebral canal
What are the clinical indications for MRI?
Soft tissue injuries
Ligament, tendon, cartilage tears
Bone tumors, stress fx, osteomyelitis and AVN
Anything involving the marrow of bone or anything that happens early in bone- cant see these things on radiographs because there has not been enough time for density changes in bone
IV disc pathology
Bulges, height, dessication, etc.
What are the limitations of an MRI?
Imaging cortical bone (has very little water)
Length of time
Claustrophobia
Orthopedic hardware
High cost
What are the contraindications for an MRI?
Metal
Can cause malfunction of pacemakers
Work station should be kept in a different room- magnetic field can cause projectiles of metal objects.
What is diagnostic ultrasound?
Imaging is based on tissue absorption of sound waves and reflection of sound waves at tissue interfaces
Non-invasive and does NOT use ionizing radiation (safe)
In-expensive compared to other imaging modalities
How does diagnostic ultrasound work?
Production of soundwaves
Electrical charges are applied to a crystal which causes it to move (reverse piezoelectric effect)-
Wavelike motion of a crystal inside the transducer produces US waves
Reception
Waves are reflexed from tissue which causes the crystals to deform which produces electric charges on the opposing surfaces of the crystal (piezoelectric effect)
This electricity forms the data from which the image is constructed
What is therapeutic ultrasound and what does it do that diagnostic ultrasound does not do?
Therapeutic US causes a rise in tissue temperature; diagnostic US does not
How is ultrasound described compared to how MRIs, CTs, and radiographs
US is described as relative to the structures being examined
MRI, CT, and radiographs use orthogonal planes
Were the planes associated with an ultrasound?
Longitudinal
Aligned with long axis of muscle or structure
Transverse
Cross-sectional view of muscle or structure
What type of image and plane is this?
Ultrasound, longitudinal
What type of image in plain is this?
Transverse, ultrasound
What determines signal intensity in an ultrasound?
Reflection from tissues depends on
Nature of tissue interface
Angle of the beam
Type of tissue
What is Echogenecity and what are the types?
tissue’s ability to return an echo or signal during the US exam
Hyperechoic
Hypoechoic
Anechoic
What is the intensity of different types of tissues to ultrasounds?
US does not penetrate bone thus bone is hypoechoic
BUT, bone soft tissue interface is very hyperechoic
Tendons and ligaments are hyperechoic relative to muscle
Should see distinct parallel fiber patterns
Muscle- hyperechoic with parallel fibrous hyperechoic bands
Nerve hyperechoic relative to muscle
What are the clinical uses of ultrasound?
Generally to image soft tissues
Muscles
Approx = to MRI
Tendon imaged better than MRI
Ligaments = MRI
Pediatric joints- physes are still open
Bone
Can predict fx risk based on strength of bone
Where the advantages of diagnostic ultrasound?
Joint can be placed in different positions
Possible to perform resisted muscle contraction, traction, compression or ligamentous stress testing
Can be a DYNAMIC test performed in real time
What are the disadvantages of diagnostic ultrasound?
Operator dependent
Does not penetrate bone
Does not cross air interfaces
Obese patients are not imaged well
