Imaging Flashcards
Appearance of cortical/compact bone on MRI
Normal compact (subchondral or cortical) bone has low signal intensity on all sequences (as low H+ concentration)
What are these sequences?
a) T1-weighted gradient echo
b) T2* gradient echo
c) T2 FSE
d) T1 gradient echo
Appearance of trabecular bone on MRI
Variable - high signal intensity on all sequences on all except fat surpressed sequences (eg STIR)
Appearance of fat and fluid on T1-weighted images
Fat - hyperintense
Water -hypointense (black-grey)
On T1, only 1 thing is white = FAT
(Note hypointense fluid in DIP and NB - red arrows)
Appearance of fat and fluid on T2-weighted images
On T2 - 2 things are white; fat and water
Trabecular bone and synovial fluid are both hyperintense. The easiest way to distinguish T1 and T2 images is to observe the signal intensity of fluid.
How to differentiate fluid from sclerosis
Need to look at multiple sequences
Fluid and sclerosis are indistinguishable on T1-weighted images. However fluid will have intermediate-high signal intensity on T2, STIR and PD images
Not possible to identify sclerosis on fat surpressed images
Care re T2* images which are susceptible to phase cancellation artefacts (hypointensity where there is equal amount of fat and water within bone)
PD and T2-weighted FSE sequences provide a definitive way to identify sclerosis, when compared with the T2* gradient-echo images as there is no overlap between the appearance of fluid and sclerosis on these sequences
Which imaging sequence is particulary susceptible to phase cancellation artefact? What does this artefact represent?
T2* gradient echo (esp on the Hallmarq system)
Represents area within the bone were the amount of fat and water are equal, rx in relative hypointensity on T2*.
Determine wether fat or fluid on STIR (fluid hyperintense) and T1 (sclerosis or fluid hypointense, fat hyperintense).
Appearance of bone sclerosis on MR
Reduced signal intensity on all sequences)
Appearance of bone marrow lesion (oedema) on MRI
Increased signal intensity on fat surpressed images
Low intensity on T1
High on T2 (subject to arteface eg fat-water cancellation artefact esp on T2*)
Influence of standing MR on pre-operative fracture planning reported by Genton et al (VS 2019)
MRI had major relevance to surgical repair (big impact on sx planning) in 12/31 (38.7%) horses, intermediate relevance in 14/31 (45.1%) (modified sx plan or approach to some degree) and minor relevance in 5/31 (didn’t change approach/plan)
The images were particularly useful (transverse slices) to study fracture geometry, especially in comminuted PP and spiral condylar fractures
CT remains the gold standard for fracture evaluation, and the authors do not recommend use of sMRI when CT is available unless a concomitant lesion is suspected
What angle does magic angle artefact occur at and how does it appear?
Occurs when the tissue fibres are oriented at ap- proximately 55° to the main magnetic field.
Appears as an increased signal intensity and is seen commonly at the DDFT insertion and in the CLs of the DIPj. Also been documented within the proximal aspect of the oblique sesmoidean ligaments during standing MRI
