msk imaging guidelines
DESCRIPTION
ÂTRANSCRIPT
Musculoskeletal Imaging Guidelines
Kerry Kallas, MDMusculoskeletal Radiologist
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Imaging Modalities
⢠Radiography⢠Arthrography⢠Computed Tomography (CT)⢠Magnetic Resonance Imaging (MRI)⢠------------------------------------------------⢠Ultrasound⢠Nuclear Medicine
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Radiography
⢠Technologiesâ Screen-Filmâ Computed Radiographyâ Digital Radiography
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Radiography
⢠Advantagesâ Convenientâ Relatively inexpensive
⢠Disadvantagesâ 3D volume projected on 2D imageâ Ionizing radiation
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Arthrography
⢠Techniqueâ Localize joint space under fluoroscopyâ Insert needle into joint along axis of x-ray beamâ Confirm intra-articular position of needle tip with
injection of radiopaque contrast (Omnipaque 240)â Injection of full amount of contrast⢠Arthrography: Omnipaque 240 (full strength)⢠CT Arthrography: Omnipaque 240 (full strength)⢠MR Arthrography: Omniscan (gadolinium â 1:250)
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Arthrography
⢠Volume of contrast depends on jointâ Shoulder: 15ccâ Elbow: 10ccâ Wrist: 2ccâ Hip: 15ccâ Knee: 30ccâ Ankle: 10ccâ Toe: 1cc
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Arthrography
⢠Advantagesâ Functional exam to evaluate for rotator cuff tearsâ Not used very often with other jointsâ Can be combined with CT, MR
⢠Disadvantagesâ Allergic reactions to contrastâ Invasiveâ Relatively low exposure to ionizing radiationâ Post procedural pain
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Computed Tomography (CT)
⢠Technologiesâ âSpiral Scannerâ: buzz words from 1990âsâ Incremental versus Helical techniquesâ Multislice configurations (4,16,64âŚ320)
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Computed Tomography (CT)
⢠Image Productionâ Need to select parameters prior to scan (slice
thickness, overlap, FOV, scan mode, kV, mA, pitch)â 3D anatomic volume reduced to series (âstackâ) of
2-D imagesâ Reconstructions in any plane⢠âIsotropicâ voxels allow imaging reconstructions in any
plan that have identical resolution to original scan
â 3-D reconstructions
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Computed Tomography (CT)
⢠Advantagesâ Good spatial resolutionâ Good bone-soft tissue contrast resolutionâ Typical slice thicknesses of 0.6 â 1.2 mm for
extremitiesâ Fast, not much patient movement during examâ Patient comfort
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Computed Tomography (CT)
⢠Disadvantagesâ Much higher doses of ionizing radiation than
radiographyâ Higher cost, but not most expensiveâ Poor soft tissue contrast resolutionâ Poor at differentiating soft tissue pathology (fluid,
edema) from normal anatomyâ Contrast enhanced studies not effective for
extremitiesâ Allergic reactions to contrast if administered
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Computed Tomography (CT)
⢠MSK Indicationsâ Complex fractures or acute traumaâ Small fracture fragments or intra-articular bodiesâ Fracture healing (nonunion, delayed unionâ Patients who are MR incompatible (e.g.
pacemakers, aneurysm clips)â Patients with metal hardware near area of interest⢠Suture anchors⢠ORIF hardware
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CT Arthrography
⢠Combined study of Arthrography and CTâ Perform arthrogram first using Omnipaque 240â CT scan immediately after arthrographyâ Cannot wait too long to image as the radiopaque
contrast is absorbed by the body fairly quickly⢠Reconstruct in standard orthogonal planes
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CT Arthrography
⢠Advantagesâ Contrast outlines normal intra-articular structures
that cannot be separated with conventional CTâ Contrast distends the joint capsule and moves
capsular structures away from each otherâ Contrast that extends into abnormal areas implies
pathology (tears, chondromalacia)â Need to know what normal anatomy is first!
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CT Arthrography
⢠Disadvantagesâ All the same individual disadvantages of
Arthrography and CTâ Higher cost for combined studyâ Same soft tissue contrast resolution limitations
where there is no contrast⢠Bursal surface rotator cuff tears
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CT Arthrography
⢠MSK Indicationsâ Patients who are not MR compatible andâŚâ Need to evaluate intra-articular structures (other
than bony structures)â CT only of joints provides LIMITED information⢠Bone detail⢠Very little soft tissue detail (exceptions: tendons, fat)
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Magnetic Resonance Imaging (MRI)
⢠Technologiesâ 1.5 Tesla field strength most commonâ 3.0 Tesla available, but higher cost (usually
hospitals, less outpatients centers)â Low field scanners (0.2T â 1.0T)⢠Open scanners⢠Extremity scanners
â No difference in reimbursement from insuranceâ Marked difference in image quality and capability
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Magnetic Resonance Imaging (MRI)
⢠Image Productionâ Need to select many more scan parameters prior
to scanning (usually contained in preprogrammed âprotocolâ)
â Not usually able to reconstruct images (slice thickness usually much larger than pixel size)
â âIsotropicâ voxels allow reconstructions in any plane⢠Usually gradient echo sequences⢠Now there are isotropic âspin echoâ 3-D sequences
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Magnetic Resonance Imaging (MRI)
⢠Intravenous Contrastâ Volume based on weight, usually max 20cc
Omniscanâ Indications⢠Synovitis⢠Cellulitis and other infections⢠Masses (differentiate solid from cystic)⢠Ischemia/Avascular Necrosis⢠Indirect MR arthrography (not common)
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Magnetic Resonance Imaging (MRI)
⢠Advantagesâ No ionizing radiationâ Superb soft tissue and bone contrast ⢠Cortex⢠Bone marrow and fat⢠Hyaline cartilage⢠Fibrocartilage (meniscus, labrum)⢠Ligaments, tendons⢠Fluid⢠Muscle
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Magnetic Resonance Imaging (MRI)
⢠Disadvantagesâ Less in-plane spatial resolution than CT⢠CT matrix typically 512⢠MRI matrix usually 256, 320, 384, occasionally 512
â Less on-axis spatial resolution than CT⢠CT slice thicknesses usually less than 1.0 mm⢠MRI slice thickness usually 3.0 â 4.0 mm for MSK⢠Greater partial volume averaging
â Poor discrimination between fat and bone marrow
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Magnetic Resonance Imaging (MRI)
⢠Disadvantagesâ Longer scan times (20-30 minutes)⢠Patient needs to lays still for longer time⢠Greater motion artifact
â Higher costs than CTâ Claustrophobia, may require sedationâ Need to screen for MRI incompatibilities (metal
fragments in eyes, pacemakers, etc.)â Greater number of imaging artifacts
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Magnetic Resonance Imaging (MRI)
⢠MSK Indicationsâ Usually preferred examination after Radiography
for evaluation of internal derangement of jointsâ Excellent soft tissue resolution with need for
contrastâ Usually good spatial resolution (although less than
CT)â Differentiates pathology (fluid, edema) from
normal anatomy
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MR Arthrography
⢠Combined study of Arthrography and MRIâ Perform arthrogram first using gadolinium
contrast agent (Omniscan, 1:250)â MRI performed soon after arthrography (not as
urgent as CT to image immediately)⢠Image using combination of standard and
âgadolinium sensitiveâ sequencesâ Gadolinium bright on T1-weighted imagesâ Add fat suppression for MSK imaging (FST1)
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MR Arthrography
⢠Advantagesâ Contrast distends joint capsule and capsular
structuresâ Contrast surrounds and separates normal intra-
articular structuresâ Leakage of contrast into abnormal locations may
imply pathologyâ May add anesthetic to contrast to determine pain
relief (intra-articular versus extra-articular source)
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MR Arthrography
⢠Disadvantagesâ All the same individual disadvantages of MRI and
Arthrographyâ Higher cost with combined studies
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MR Arthrography
⢠MSK Indicationsâ Shoulder: Labral tearâ Elbow: OCD, MCL tearâ Wrist: TFC, SLL tearâ Thumb: UCL tearâ Hip: Labral tearâ Knee: OCD, post-op meniscusâ Ankle: OCDâ Toe: Plantar plate tearâ Post-op evaluations
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Ultrasound
⢠Advantagesâ No ionizing radiationâ Lower cost than CT and MRIâ May visualize superficial structures at high
resolution⢠Tendons⢠Masses
â Tolerated by patients very wellâ May perform US guided procedures
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Ultrasound
⢠Disadvantagesâ Requires highly skilled/experienced technologist
or physicianâ Operator must know underlying anatomyâ Takes time to perform examâ Real time exam versus imagingâ Convincing surgeons to operate based on US
images
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Nuclear Medicine
⢠MSK Indicationsâ Bone Scan⢠Metastatic disease
â Indium (I111) labeled WBC⢠Osteomyelitis in Charcot joint (diabetic)
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