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

• Technologies– Screen-Film– Computed Radiography– Digital Radiography

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Radiography

• Advantages– Convenient– Relatively inexpensive

• Disadvantages– 3D volume projected on 2D image– Ionizing radiation

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Arthrography

• Technique– Localize joint space under fluoroscopy– Insert needle into joint along axis of x-ray beam– Confirm intra-articular position of needle tip with

injection of radiopaque contrast (Omnipaque 240)– Injection of full amount of contrast• Arthrography: Omnipaque 240 (full strength)• CT Arthrography: Omnipaque 240 (full strength)• MR Arthrography: Omniscan (gadolinium – 1:250)

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Arthrography

• Volume of contrast depends on joint– Shoulder: 15cc– Elbow: 10cc– Wrist: 2cc– Hip: 15cc– Knee: 30cc– Ankle: 10cc– Toe: 1cc

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Arthrography

• Advantages– Functional exam to evaluate for rotator cuff tears– Not used very often with other joints– Can be combined with CT, MR

• Disadvantages– Allergic reactions to contrast– Invasive– Relatively low exposure to ionizing radiation– Post procedural pain

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Computed Tomography (CT)

• Technologies– “Spiral Scanner”: buzz words from 1990’s– Incremental versus Helical techniques– Multislice configurations (4,16,64…320)

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Computed Tomography (CT)

• Image Production– Need to select parameters prior to scan (slice

thickness, overlap, FOV, scan mode, kV, mA, pitch)– 3D anatomic volume reduced to series (“stack”) of

2-D images– Reconstructions in any plane• “Isotropic” voxels allow imaging reconstructions in any

plan that have identical resolution to original scan

– 3-D reconstructions

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Computed Tomography (CT)

• Advantages– Good spatial resolution– Good bone-soft tissue contrast resolution– Typical slice thicknesses of 0.6 – 1.2 mm for

extremities– Fast, not much patient movement during exam– Patient comfort

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Computed Tomography (CT)

• Disadvantages– Much higher doses of ionizing radiation than

radiography– Higher cost, but not most expensive– Poor soft tissue contrast resolution– Poor at differentiating soft tissue pathology (fluid,

edema) from normal anatomy– Contrast enhanced studies not effective for

extremities– Allergic reactions to contrast if administered

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Computed Tomography (CT)

• MSK Indications– Complex fractures or acute trauma– Small fracture fragments or intra-articular bodies– Fracture healing (nonunion, delayed union– Patients who are MR incompatible (e.g.

pacemakers, aneurysm clips)– Patients with metal hardware near area of interest• Suture anchors• ORIF hardware

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CT Arthrography

• Combined study of Arthrography and CT– Perform arthrogram first using Omnipaque 240– CT scan immediately after arthrography– 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

• Advantages– Contrast outlines normal intra-articular structures

that cannot be separated with conventional CT– Contrast distends the joint capsule and moves

capsular structures away from each other– Contrast that extends into abnormal areas implies

pathology (tears, chondromalacia)– Need to know what normal anatomy is first!

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CT Arthrography

• Disadvantages– All the same individual disadvantages of

Arthrography and CT– Higher cost for combined study– Same soft tissue contrast resolution limitations

where there is no contrast• Bursal surface rotator cuff tears

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CT Arthrography

• MSK Indications– Patients who are not MR compatible and…– Need to evaluate intra-articular structures (other

than bony structures)– 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)

• Technologies– 1.5 Tesla field strength most common– 3.0 Tesla available, but higher cost (usually

hospitals, less outpatients centers)– Low field scanners (0.2T – 1.0T)• Open scanners• Extremity scanners

– No difference in reimbursement from insurance– Marked difference in image quality and capability

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Magnetic Resonance Imaging (MRI)

• Image Production– Need to select many more scan parameters prior

to scanning (usually contained in preprogrammed “protocol”)

– Not usually able to reconstruct images (slice thickness usually much larger than pixel size)

– “Isotropic” voxels allow reconstructions in any plane• Usually gradient echo sequences• Now there are isotropic “spin echo” 3-D sequences

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Magnetic Resonance Imaging (MRI)

• Intravenous Contrast– Volume based on weight, usually max 20cc

Omniscan– 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)

• Advantages– No ionizing radiation– 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)

• Disadvantages– Less in-plane spatial resolution than CT• CT matrix typically 512• MRI matrix usually 256, 320, 384, occasionally 512

– Less on-axis spatial resolution than CT• CT slice thicknesses usually less than 1.0 mm• MRI slice thickness usually 3.0 – 4.0 mm for MSK• Greater partial volume averaging

– Poor discrimination between fat and bone marrow

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Magnetic Resonance Imaging (MRI)

• Disadvantages– Longer scan times (20-30 minutes)• Patient needs to lays still for longer time• Greater motion artifact

– Higher costs than CT– Claustrophobia, may require sedation– Need to screen for MRI incompatibilities (metal

fragments in eyes, pacemakers, etc.)– Greater number of imaging artifacts

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Magnetic Resonance Imaging (MRI)

• MSK Indications– Usually preferred examination after Radiography

for evaluation of internal derangement of joints– Excellent soft tissue resolution with need for

contrast– Usually good spatial resolution (although less than

CT)– Differentiates pathology (fluid, edema) from

normal anatomy

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MR Arthrography

• Combined study of Arthrography and MRI– Perform arthrogram first using gadolinium

contrast agent (Omniscan, 1:250)– MRI performed soon after arthrography (not as

urgent as CT to image immediately)• Image using combination of standard and

“gadolinium sensitive” sequences– Gadolinium bright on T1-weighted images– Add fat suppression for MSK imaging (FST1)

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MR Arthrography

• Advantages– Contrast distends joint capsule and capsular

structures– Contrast surrounds and separates normal intra-

articular structures– Leakage of contrast into abnormal locations may

imply pathology– May add anesthetic to contrast to determine pain

relief (intra-articular versus extra-articular source)

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MR Arthrography

• Disadvantages– All the same individual disadvantages of MRI and

Arthrography– Higher cost with combined studies

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MR Arthrography

• MSK Indications– Shoulder: Labral tear– Elbow: OCD, MCL tear– Wrist: TFC, SLL tear– Thumb: UCL tear– Hip: Labral tear– Knee: OCD, post-op meniscus– Ankle: OCD– Toe: Plantar plate tear– Post-op evaluations

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Ultrasound

• Advantages– No ionizing radiation– Lower cost than CT and MRI– May visualize superficial structures at high

resolution• Tendons• Masses

– Tolerated by patients very well– May perform US guided procedures

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Ultrasound

• Disadvantages– Requires highly skilled/experienced technologist

or physician– Operator must know underlying anatomy– Takes time to perform exam– Real time exam versus imaging– Convincing surgeons to operate based on US

images

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Nuclear Medicine

• MSK Indications– Bone Scan• Metastatic disease

– Indium (I111) labeled WBC• Osteomyelitis in Charcot joint (diabetic)

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