MRI MSK 1 Flashcards
Why is MRI good for MSK?
- Great detail
- Very sensitive to disease and trauma
- joints don’t move
What are the common sequences for MSK MR?
T1 : SE, FSE/TSE
T2 : FSE/TSE
PD: FSE/TSE
Fat saturation : (STIR, fatsat, Dixon) (T1, T2 or PD)
Volume scans - isotopic
What changes may you see in a T1 weighted Joint?
Synovial fluid
Blood products
Effusion
Reactive changes
What are the technical factors of T1 weighted images?
~ fluid demonstrates as low signal
~ inherently high SNR
~ can use smaller FOV
~ higher matrix resolution
~ ideally true spin echo contrast
What is T1 good for looking at MSK?
Trabeculae patterns
Good contrast between bone and soft tissue
What are the technical factors of T2 weighted images?
- fluid demonstrated as high signal
- demonstrates pathology well
- Higher SNR
- FSE/TSE used for T2 or PD weighting usually t1 in MSK imaging
What are the methods of fat saturation? And how do they achieve this?
STIR and chemical fat sat
STIR = (Short T1 inversion recovery) suppressed by time inversion sequence
Chemical FS = fat suppression by radio frequency, pulse centred on fat peak.
Why is it needed to suppress fat?
To suppress the signal from medullary fat
To demonstrate choncral cartilage defects
To demonstrate oedema/ bone bruising (as high signal).
Why is MRI useful in the pelvis?
Ruling out occult fractures - NOF, pubic rami, sacrum etc
Tendon injuries, bursitis, or, neoplasms, infection
Often after inconclusive X-ray
What is the common sequence for an MSK pelvis?
Coronal / axial T1 and STIR
What is involved with an ankle MRI?
Chimney dedicated coil - foot an ankle
Foot and leg at 90 degreees
Limited rotation for joint
Use immobilisation pads
What is the sagittal positioning for an ankle MRI?
Why do we use sagittal?
Sagittal perpendicular to joint
Better demonstration of ligaments
Cover laterally to demonstrate ligaments
Use coronal to ensure perpendicular to tibia.
What is the coronal positioning for an ankle MRI?
Coronal - perpendicular to talus through the malleoli
Cover front to back to include Achilles and anterior tendons
Use sagittal scan to ensure perpendicular to tibia
What is the positioning or an axial ankle MRI?
Axial - perpendicular to tibia parallel to talus joint
Use sag and cor to plan slices
What does the axial PD fat sat demonstrate around the tendons or ligaments?
High signal in pathology
What does oCD stand for?
Osteochondritis dissecans
What causes OCD?
Original inversion injury
- Compressor force
- Bone is less elastic than cartilage
- Bone fracture without Chondral fracture
- Healing dependent on overlying cartilage (stages 1-4)
Where and who does oCD mainly affect?
Elbow and knee
Men more than women Moore in adolescence
What are the problems associated with osteochondral defects form an inversion injury?
Can be hard to clinically diagnose
May become necrotic
Can develop into a loose body
What are the goals of imaging for Osteochondral defects?
To detect, localise and classify prior to treatment
What is stage 1 OCD?
Compression fracture
What is stage 2 OCD?
Partially avulsed
What is stage 3 OCD?
Avulsed but un-displaced
Cortical fragments separated by intermediate signal intensity, material from the concave, bony defect beneath it .
What is stage 4 OCD?
Displaced osteochondral fragment - crater develops beneath thee fragment
What is involved with scanning the Achilles tendon?
The ankle coil, extremity coil, head coil or torso coil may be used
Positioning : neutral position in plantar flexion, otherwise gaps due to rupture maybe missed.
Where is the insertion of the Achilles tendon?
High into the calf muscle
The water shed is 2-4 cm above the insertion
What are the clinical indications for shoulder MRI?
- Pain
- Restricted movement
- Recurrent dislocations
What is the positioning for shoulder MRI?
Pt supine
Shoulder externally rotated - extends tendon to assist in detecting pathology
Avoid hand over abdo - keep hand still
Immobilised strap arm down
Shoulder off centre for optimism fat sat
What is the planning positioning for shoulder MRI?
Axial positioning
Cover from AC joint to sub glenoid labrum
4mm slice and 1mm gap
Used as a localiser for coronal and sag obliques
What is the planning for coronal obl for shoulder MRI?
Coverage of joint capsule
3mm slice and 1 mm gap
Perpendicular to glenoid
What are the sequences for MRI shoulder? And what are their benefits?
T1 SE - Coronal obl
= Excellent, anatomical view of the muscles and ligaments of the shoulder
= Effusion and pathology demonstrated as low signal .
T1 SE - sag obl
= used to assess the degree of impingement of the supraspinatous muscle by the AC joint
= Demonstrates bone, bruising
What is the planning for Saggital obl MRI shoulder?
3mm slice and 1 mm gap
Parallel with glenoid
Perpendicular to coronal
What is the clinical presentation of rotator cuff tear?
- painful movement in all directions
- restriction on abduction and flexion
- acute pain
- history of trauma or overuse
- problems with ADL
What is impingement syndrome in the shoulder?
- degeneration of tendon
- Swelling - impingement against the chromium and coracoacromial ligament
- Spur formation
- Supraspinous, eventually tears
What is a bank art lesion?
Avulsion of labrum From anterior Glenoid - diagnosed when fluid separates labour from glenoid
What are MR arthrograms?
What are they used to detect?
Arthrography gives additional detail if intra-articular structures
Useful for clarification of inconclusive findings on a standard MRI
Better detection and assessment of :
- Small, loose bodies
- Cartilage flaps
- Glenoid labour tears
- Better assessment of the undersurface of the rotator cuff ( a frequent site of partial tears)
What is the positioning for a wrist MRI?
Dedicated coil
Better with pt prone (superman position) however supine with wrist by side can also be done (my need wide bore)
Uncomfortable position - superman
What is the positioning for a wrist MRI?
Neutral position - aligned long access of radius with central metacarpal axis
Incorrect positioning can result in pseudo instability of capitolunate angle on the sagittal.
What are the sequences used for wrist MRI?
~ T1 - anatomy
~ Fatsat (STIR if metallic artefact) - bone oedema /fractures
~ T2* - cartilage / ligaments / TFCC
~
axial useful for tendons and ligaments in cross section
What does TFCC stand for?
Triangular fibrocartilage complex
Where it’s the TFCC?
In the wrist Between the ulna and carpal bones
What are the technical consideration for wrist imaging?
High spatial resolution
- high matrices
- thin slices
- interleaving
What are the common places of scaphoid fractures?
70% - occur at the waist
20% occur at the proximal pole
Non-union fractures may result in AVN
