HSS Manual Ch. 7 - Diagnostic Imaging Techniques

From the HSS manual of Rheumatology and Outpatient Orthopedic Disorders


Numerous diagnostic imaging techniques may be used to supplement history, physical examination, and laboratory tests in the evaluation of bone and joint disease. The choice of the imaging techniques to use and in what sequence depends on the sensitivity and specificity of the technique for a particular problem, on the availability, cost, and risk, and experience in its use.

The goal is to answer the question raised by the clinician in the shortest time at the least cost and risk to the patient. Prior consultation with the radiologist and providing clinical information when ordering an imaging examination will help the radiologist  and technologist to tailor the examination to the problem under investigation.

IMAGING TECHNIQUES

  1. Radiography is usually the initial diagnostic imaging method in the evaluation of bone and joint pain, as it is readily available and of relatively low cost compared with other imaging methods. It provides excellent detail of bony anatomy and soft tissue calcification. Lucency, sclerosis, and periosteal reaction of indicate bony abnormality. Cartilage, muscle, ligaments, tendons, and synovial fluid all appear with the same soft-tissue density on roentgenography, which limits evaluation of abnormalities of these tissues. Cartilage destruction can be diagnosed if joint space narrowing is present. (Fig. 7-1) Bony erosions can be seen around the joints.  Determination of osteoporosis can be difficult as variations in technique can affect the apparent density on roentgenograms.  Bony alignment can be determined and measured.  Synovitis may be detected in the knee, elbow, and ankle because of the displacement of adjacent fat pads, but it cannot be reliably detected in the hip and shoulder.  Other imaging methods, including MRI, radionuclide scanning, and ultrasonography may show bone and joint abnormality when roentgenograms are normal. (Fig. 7-2) Radiographc real time imaging is done by fluoroscopy. C-arm fluoroscopes which can be rotated and tilted aid in localization during surgical procedures (e.g., internal fixation of fractures and osteotomies); invasive radiologic procedures (e.g., myelography, nerve root, facet, and epidural spine injections, percutaneous needle biopsy, discography, joint aspiration and injection, and arthrography). (Fig. 7-2c) Fluoroscopy with videorecording can also be used for the evaluation of motion. Care must be taken to limit fluoroscopic time to avoid excessive radiation exposure.


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FIG. 7-1

Oblique radiographs of the right and left hands and wrists in a woman with rheumatoid arthritis show narrowing of the radiocarpal, midcarpal, carpometacarpal, second metacarpophalangeal, and radioulnar joints, with periarticular osteoporosis and erosions.


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FIG. 7-2a


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FIG. 7-2b


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FIG. 7-2c

FIG. 7-2 In a patient who had pain and swelling of the metatarsophalangeal joint of the great toe with normal radiographs, the proton density (a) and STIR (b) showed osteoarthrosis with articular cartilage narrowing, bone marrow edema pattern, collapse of the subchondral bone, synovitis, and thickening of the medial ligaments (see arrows). Using C-arm fluoroscopy the tube was tilted to make the joint tangential to the x-ray, allowing a needle to be inserted into the joint for aspiration and injection of local anesthetic and corticosteroids (c). Contrast was injected confirming the intra-articular position of the needle.
  1. Radionuclide scanning

    1. Bone scanning with use of technetium 99m phosphate complexes has been used most frequently in the evaluation of metastatic disease to the skeleton and has largely replaced routine roentgenographic skeletal surveys for this purpose except for multiple myeloma. It is also used for the evaluation of benign bone disease, as abnormalities may be detected that are not visible on roentgenograms. Bone scanning detects physiologic changes in the bone, in comparison with the anatomic changes seen on roentgenograms. Increased uptake of radionuclide on a bone scan is caused mainly by increased osteoblastic activity associated with new bone formation, and to a lesser degree by increased blood flow to bone. This can result from numerous causes, including infection, tumor, fractures, or synovitis. Thus, although bone scanning is sensitive in detecting abnormalities of the bones and joints, it is not specific. Three-phase bone scanning, which includes blood flow and blood pool scans, as well as static images 2 to 4 hours or more after injection, should be ordered for the evaluation of localized bone or joint pain. The early phases show vascularity, which may be helpful in diagnosing synovitis, infection, and soft-tissue abnormalities. Single-photon emission computed tomography (SPECT) may provide increased detail and can be helpful in diagnosing stress or traumatic spondylolysis and in detecting photopenic areas in avascular necrosis. Radionuclide bone scanning is most useful for screening the entire skeleton to localize the site of abnormality and also for detecting stress fractures, osteoid osteomas, and evaluating painful joint prostheses.

    2. Radionuclide infection scanning
      1. Scanning with gallium citrate 67 shows increased uptake at sites of infection and some malignant neoplasms in the bones or soft tissues. It has a high sensitivity for bone and joint infection but is nonspecific, as it may show increased uptake associated with other causes of increased bone turnover, including fractures or tumors, and also shows increased uptake in noninfectious inflammatory conditions, such as inflammatory arthritis. The specificity of a gallium scan for infection may be increased if it is compared with a bone scan. If the gallium scan shows more intense uptake than the bone scan at the affected site or if the uptake of gallium is not congruent with the uptake on the bone scan, then infection is likely. However, only one-third or fewer of bone infections meet these criteria. False-negative gallium scans may be seen in chronic infection or if the patient is treated with antibiotics before the scan is performed. Gallium scanning is preferred over white blood cell scanning for diagnosis infectious spondylitis, and for fever of unknown origin.
      2. Scanning with indium 111- or technetium 99m-labeled white blood cells can detect bone or joint infection, due to migration of the radiolabelled WBCs to areas of infection or inflammation. Uptake of WBCs also occurs in non infected bone marrow. Comparison of the WBC scan should be done with a bone marrow scan with radiolabelled colloid, such as Tc99m sulfur colloid, and uptake of WBCs not matched by on the bone marrow scan is abnormal. (Fig. 7-3) The specificity is greater than bone scanning or gallium scanning for infection bone and joint infection, however, mismatched uptake may also be seen in noninfectious inflammatory conditions.


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FIG. 7-3

There is abnormal increased uptake of In-111 white blood cells in the right femur (arrow) and thigh, not matched by a similar area on the Tc-99m bone marrow scan indicating active infection in this patient.
    1. Positron emission tomography (PET) uses 18F-fluorodeoxyglucose (FDG) as a scanning agent. FDG acts like glucose and is transported into cells and trapped. Malignant tumors and other conditions with high metabolic activity such as infection have increased glycolysis and increased uptake of FDG. PET CT combines simultaneous PET and CT allowing exact anatomic localization of areas of increased uptake of FDG. PET is highly sensitive for malignant soft tissue and bone neoplasms however it has a lower specificity. It has a high cost, and reimbursement by medical insurance is limited to a relatively few indications at this time.

  1. Computed tomography (CT) provides better bone detail than does roentgenography. Thin (1mm or less) sections with multislice CT scanners provide high resolution multiplanar (axial, coronal, and sagittal)images. This has almost completely replaced roentgenographic tomography. 3D images can also be created. Although CT provides better contrast for evaluation of soft tissue than does roentgenography, MRI is superior for soft tissue abnormalities. Some of the indications for musculoskeletal CT include; evaluation of fracture displacement and alignment, bone tumors, and healing of fractures, joint arthrodesis, and surgical fusion in the spine. CT scans are routinely obtained immediately after myelography, and discography. Metallic orthopedic hardware causes beam hardening artifact on the scans, however use of technique with high kilovoltage and high milliamperage, along with reformatted images allows diagnostic images to be obtained in many cases. (Fig. 7-4) CT guidance for interventional procedures allow exact needle placement for bone and soft tissue biopsies, radiofrequency ablation of osteoid osteomas and other neoplasms, and spine injections that may be difficult to perform under fluoroscopy. Radiation exposure is higher for CT than with roentgenography, and there is no radiation exposure with MRI and ultrasound.


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FIG. 7-4

Reformatted coronal and sagittal reformatted images show large areas of osteolysis (arrows) around the acetabular component of a total hip prosthesis.
  1. Magnetic resonance imaging (MRI) has the advantage of providing multiplanar imaging with both anatomic and physiologic information that combines many of the capabilities of the other imaging methods in one examination, and also provides information for diagnosis of bones, joints, and soft tissue not available with other methods.
     
    1. Technique:  The appearance of MRI scans depends on the imaging sequence used. The spin echo technique is the most commonly used. T1-weighted images have short echo time (TE), short repetition time (TR), intermediate weighted or proton density (PD) images, have short TE and long TR, T2 weighted images have long TE and long TR. Fluid is dark (low signal) on T1 and bright (high signal) on T2. Fat is bright on TI and intermediate on T2. Cortical bone has low signal on T1 and T2. Bony abnormalities can be evaluated due to alterations in the marrow fat. Pathologic processes (neoplastic disease, infection, fractures) will exhibit low or intermediate signal on T1-weighted sequences and high signal on T2. Intermediate or PD images do not show differences in contrast of the tissues as well as T1 or T2; however, the resolution of the images is greater, allowing better evaluation of the morphology. (Fig. 7-2a) Fat suppression techniques such as short tau inversion recovery, and chemical shift spin echo cause fluid to become very bright and fat dark providing good contrast for detecting pathology. (Fig. 7-2b) High resolution MRI images are needed to evaluate many abnormalities such as labral tears of the shoulder and acetabulum, ligament tears in the wrist and elbow and articular cartilage in the joints, and can be obtained by adjusting the scanning parameters, using a smaller field of view, and using surface coils instead of body coils for smaller structures. Various sequences are used for imaging of articular cartilage. Gadolinium diethylenetriamine pentaacetic acid (GD-DTPA) is an MRI contrast agent that, when used in typical doses (0.1 mmol/kg of body weight), acts primarily to shorten T1 relaxation times. Thus, regions that readily enhance with contrast will appear bright on T1-weighted images. In the evaluation of the postoperative spine, contrast may help to distinguish scar from recurrent disk herniation (Fig. 7-3-2). Postoperative scar is felt to enhance with contrast by virtue of the rich vascularity of epidural granulation tissue. Conversely, the avascular adult disk will not demonstrate similar signal enhancement. A contrast-enhanced MRI examination performed long after surgery may not prove as reliable, as scar tissue may become progressively fibrotic, with less discernible contrast enhancement. Inflammatory tissue will enhance with gadolinium, which may help to define an abscess and differentiate from another fluid collection. Relative contraindications to GD-DTPA administration include hemolytic anemia, as the agent may promote extravascular hemolysis. Because GD-DTPA is cleared via glomerular filtration, caution should be utilized in patients with impaired renal function. The most common reported adverse reaction is mild headache (<10% of patients).

    2. Indications:  MRI has become the imaging method of choice for many abnormalities including: evaluation of internal derangement of the knee (meniscal tears; cruciate, collateral, and quadriceps mechanism tears; bone contusion), osteonecrosis, rotator cuff tears and glenohumeral instability, tendon, ligament, and muscle tears and other abnormalities, back pain, bone and soft-tissue tumors, occult fracture, and evaluation of the brain and spinal cord. Articular cartilage abnormalities including chondromalacia, fissuring, and partial and full thickness cartilage defects can be seen. Joint erosions and synovitis can be detected in patients with normal radiographs. (Fig. 7-2a, b)

    3. Contraindications to MRI include the presence of pacemakers, aneurysm clips, some prosthetic otologic and ocular implants, and some bullet fragments. Clinical concern is increased when the metallic object is anatomically close to a vital vascular or neural structure. Most prosthetic heart valves are felt to be safe for MRI. In addition, most orthopedic materials and devices are considered safe, including stainless steel screws and wires. Prior knowledge of the specific type (manufacturer, material) of metallic implant is essential before the patient is exposed to a strong magnetic field. However, ferromagnetic metallic implants will cause image artifact, with large areas of signal void and adjacent high signal (“flare” response), which may interfere with accurate image interpretation. Using sequences designed for limiting metal artifact even in the presence of orthopedic hardware valuable information can be obtained, about possible infection, fracture, loosening, and osteolysis.

  2. Ultrasonography may be used to evaluate soft-tissue masses and characterize them as either cystic or solid. Popliteal cysts can easily be detected. Tendons are more echogenic than muscle and can be evaluated for continuity and inflammation. Tenosynovitis can be detected as fluid in the tendon sheath. Ultrasonography has been used in the shoulder for evaluation of the rotator cuff tendons. Complete and partial tears and tendinopathy can be diagnosed. Tendons in most other parts of the body can be evaluated in a similar manner. Plantar fasciitis can be diagnosed by evaluating the thickness and appearance of the plantar fascia. Calcific tendinitis can be detected as focal areas of high echogenicity. Injection of soft-tissue ganglia, calcific deposits, tendon sheaths, and interdigital neuromas can be performed under ultrasound guidance. (Fig. 7-5) Foreign bodies in the soft tissue can be localized. Ultrasound is used for the evaluation of developmental dysplasia of the hip in infants to determine the position of the nonossified femoral head with respect to the acetabulum.


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FIG. 7-5a


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FIG. 7-5b

FIG. 7-5 The lateral radiograph (a) of the wrist in a patient who had swelling and pain, without trauma shows a calcific deposit in the dorsal soft tissues (arrow) representing calcific tendinitis of the extensor tendons. With ultrasound guidance (b) a needle (arrow) was inserted into the calcific deposit, which was aspirated and injected with corticosteroids, which resulted in relief of symptoms in less than twenty four hours.


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