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Acupuncture Today
November, 2000, Vol. 01, Issue 11
 
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When to Order Advanced Imaging

By Hubert Chang

For musculoskeletal imaging, the most commonly ordered studies are plain film radiographs. Under certain circumstances, computerized tomography (CT) or magnetic resonance imaging (MRI) may be required to differentiate a simple strain from a more complex problem such as a tumor, infection or degenerative disorder.

There are symptoms and signs that can signify an injury or disease that may require advanced imaging or a referral to a specialist. These may include severe unrelenting pain at night; marked weakness; significant loss of range of motion; claudication; and systemic symptoms.

The use of CT or MRI should be based on your clinical findings. When a diagnosis cannot be determined, the CT or MRI should be considered only if the results will affect your treatment plan. You also need to consider the fact that these special studies are more sensitive than specific, and you will often have false positives.

The general rule of thumb is that CT is preferred for evaluating the cortex, trabecular structure and fractures. MRIs, on the other hand, are preferred for assessing soft tissue, bone marrow, ligaments, muscles, tendons and fat. MRIs are also useful in evaluating internal derangements of joints, metastatic diseases and primary tumors of the soft tissue.

Non-complex injuries such as a sprain/strain generally do not facilitate the need for advanced imaging. However, when plain film radiographs are inconclusive and conservative treatment has not helped, a CT or MRI will provide further evaluation.

When deciding to order an MRI or CT scan, a CT might be preferred because of price. However, you must consider that CT will expose your patient to ionizing radiation. A CT is also limited to scans of the axial plane, whereas MRI has the ability to image directly in a variety of planes without reconstruction. MRIs with the contrast agent Gd-DTPA (gadolinium diethylene-triamine penta-acetic acid) provide both physiologic and anatomic information. MRIs also have fewer occurrences of false negative results than CT scans.

When ordering advance imaging, we must also consider contraindications for CT and MRI. A CT is contraindicated in pregnancy and for use on children unless appropriate. MRIs are contraindicated with patients that have cardiac pacemakers or other ferromagnetic materials in their bodies such as transplants or clips.

Below is a non-exclusive list of selected indications for ordering a CT or MRI.

Indication Study Usually Performed
Bone
Fractures, trauma, deformity CT
Stress, occult, or minimally displaced fractures MRI
Bone marrow (including lymphoma, myeloma) MRI
Soft Tissues/Tumors and Masses
Benign (bone) CT
Benign (soft tissue) MRI
Malignant (soft tissue or bone) MRI
Metastases MRI or contrast MRI, bone scan
Metastases, lung CT
Hematoma
Hematoma, bleeding into tissue MRI
Epidural hematoma MRI (CT if patient is traumatized)
Hip
Avascular necrosis MRI
Osteonecrosis MRI
Transient osteoporosis MRI
Infection, Inflammation, Abscesses, Osteomyelitis MRI or contrast MRI
Intra-Articular
Intra-articular structures MR arthrography
Loose bodies in a joint CT arthrography or MR arthrography
Spine
Cauda equina syndrome Emergent MRI
Degenerative disk disease MRI or CT
Herniated disk, spinal stenosis CT or MRI (possibly with myelography)
Low back pain w/ neurological signs MRI or CT
Spondylolisthesis Plain x-ray films are best
Labrum
Tears and degeneration MRI, MR arthrography
Rotator Cuff
Full thickness tear Arthrography, MRI
Partial thickness tear MRI with contrast; MR arthrography preferred to arthrography alone and is better than conventional MRI
Shoulder impingement syndrome MRI, MR arthrography, or plain x-ray films
Meniscus
Meniscal injuries MRI

References

  • Bluemka DA, Zerhouni EA. MRI of avascular necrosis of bone. Top Magn Reson Imaging 1996;8:231-246.
  • Boegard T. Radiography and bone scintigraphy in OA of the knee comparison with MR imaging. Acta Radiol Suppl 1998;418:7-37.
  • Boegard T, Rudling O, Petersson IF, et al. Correlation between radiographically diagnosed osteophytes and magnetic resonance detected cartilage defects in the patellofemoral joint. Ann Rheum Dis 1998;57:395-400.
  • DePaulis F, Cacchio A, Michelini O, et al. Sports injuries in the pelvis and hip: diagnostic imaging. Eur J Radiology 1998;27(suppl 1):S49-S59.
  • Ryan PJ, Reddy K, Fleetcroft J. A prospective comparison of clinical examination, MRI, bone SPECT and arthroscopy to detect meniscal tears. Clin Nucl Med 1998;23:803-806.

More reference are available upon request.


Click here for more information about Hubert Chang.

 

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