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Musculoskeletal Imaging at Yale

[MRI] [MRI Arthography] [CT Scan] [CT Arthography] [CT Guided Bone Biopsy] [Joint Aspiration]

[August 2006] The section of musculoskeletal imaging at Yale performs examinations with attention to the skeleton, ligaments, muscles, and joints. We use traditional x-ray, computed tomography (CT) and magnetic resonance imaging (MRI). We work with the orthopaedic surgeons to examine problems, including arthritis, sports injuries, trauma, and tumors.

Most x-ray examinations require no preparation. At Yale, we also perform more complicated interventional procedures that require further explanation and preparation. Procedures such as joint aspirations, arthrography, biopsies, and sterotactic injections will be discussed in the following sections.

MRI

Purpose: MRI has been a tremendous advance in musculoskeletal imaging. MRI can demonstrate soft tissues such as muscle, cartilage, bone marrow, nerves and vascular structures.

How It Works: MRI in clinical medicine is based on measuring the content of water that is present in various tissue types. Once within the magnetic field, the tissue is excited by a radio frequency pulse, and as the tissue relaxes, it gives off a "resonance" which is measured and converted into an image that the radiologists can interpret. There are various types of MRI's including open, closed, high field strength and low field strength.

Preparation: Before obtaining the examination, the patient will be asked a series of pre-scan safety questions. This is to insure that there is no contraindication for the MRI examination to proceed. For example, if a patient has a small fragment of metal within the body, this may have the potential to move or become warm. If the metal is in close proximity to a vital organ or blood vessel, it may be too dangerous to allow the MRI examination to proceed. If this is the case, an x-ray or CT scan may be required to identify the metallic fragment, and its relation to vital structures. Other metallic objects such as a pacemaker, metallic stent, or clamp, may be a contraindication for an MRI examination. It is important to point out that patient's safety always comes first.

Claustrophobia, the fear of tight spaces, is relatively common. MRI is not like traditional imaging which is similar to taking a photograph with a camera. MRI is dependent on the collection of data over time. Motion will blur the image, making the exam sometimes difficult to interpret. Patients who are claustrophobic should ask their referring physician for medication that will relieve the anxiety, so as to produce an examination that can be read. Occasionally, the patient may require intravenous sedation by a nurse or physician to allow the examination to proceed.

Procedure: Upon arriving at the MRI Center, metallic or magnetic objects will be placed in a locked drawer. This includes pens, watches, keys, and credit cards. When you enter the MRI scanner, you will be placed on a movable table. The area in question such as the knee, shoulder, or ankle will be positioned in the center of the magnet and the examination will proceed. The MRI examination is made up of multiple series of images. Each series employs a different factor which will produce images that will allow for diagnosis. Following completion of the examination, you will be escorted out of the magnet area to collect your valuables. The images will now be available for the radiologist to review.

Advantages: MRI has become popular because it is painless, there is no radiation. One can obtain images in multiple plains, there is increase in soft tissue differentiation.

Disadvantages: The MRI examination is expensive.

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MRI Arthrography

Yale University has been a national leader in MRI arthrography. The study has demonstrated an improvement in diagnostic accuracy in areas including the large (shoulder, knee, and hip) and small (ankle, elbow, and wrist) joints. In addition, MRI arthrography has been extremely helpful in complicated cases such as the post-operative knee and post-operative shoulder.

Purpose: To evaluate the structures in and around joints. Joints examined include the shoulder, elbow, wrist, hip, knee, and ankle.

How It Works: Prior to the MRI examination, contrast material (normal saline and gadolinium) is injected into a joint (arthrogram). This material will help to define the anatomy, and will assist in can demonstrating tears of tendons and cartilage. MRI in clinical medicine is based on measuring the content of water that is present in various tissue types. Once within the magnetic field, the tissue is excited by a radio frequency pulse, and as the tissue relaxes, it gives off a "resonance" which is measured and converted into an image that the radiologists can interpret. There are various types of MRI's including open, closed, high field strength and low field strength

Preparation: There is no preparation required. If the patient is on a blood thinner or aspirin, it would be advantageous to discontinue this medication under the supervision of the referring physician. This is because bleeding is always a complication of any interventional procedure. If the patient has allergies to medication, iodine, shell fish, or seafood, these factors should be discussed with the radiologist prior to the beginning of the procedure. Before obtaining the examination, the patient will be asked a series of pre-scan safety questions. This is to insure that there is no contraindication for the MRI examination to proceed. For example, if a patient has a small fragment of metal within the body, this may have the potential to move or become warm. If the metal is in close proximity to a vital organ or blood vessel, it may be too dangerous for the patient to allow the MRI examination to proceed. If this is the case, a x-ray or CT scan may be required to identify the metallic fragment, and its relation to vital structures. Other metallic material such as pacemaker, metallic stent, or clamp, may be a contraindication for an MRI examination. It is important to point out that patient's safety always comes first.

Claustrophobia, the fear of tight spaces, is relatively common. MRI is not like traditional imaging which is similar to taking a photograph with a camera. MRI is dependent on the collection of data over time. Motion will blur the image, making the exam sometimes difficult to interpret. Patients who are claustrophobic should ask their referring physician for medication that will relieve the anxiety, so as to produce an examination that can be read. Occasionally, the patient may require sedation by a nurse or physician to allow the examination to proceed.

Procedure: The arthrogram is performed under direct visualization using x-ray. The patient is brought into a traditional x-ray/fluoroscopy suite, and the patient is positioned on the table. The area is marked and the skin is washed with a cleansing solution such as betadine. Local anesthetic is given into the skin and into the underlying muscle. A special needle is used to enter the designated joint, such as a shoulder or knee. The position of the needle is confirmed to be intraarticular by injecting a small amount of iodinated contrast. When this is accomplished a solution of normal saline and a preparation of gadolinium injected. The needle is removed, the area is washed, and a bandage is placed over the puncture site. The patient is escorted to the MRI scanner and the second part of the study the MRI, is performed.

Upon arriving at the MRI Center, any metallic or magnetic objects would be placed in a locked drawer. This includes pens, watches, keys, and credit cards. When you enter the MRI scanner, you will be placed on a movable table. The area in questions such as the knee, shoulder, or ankle will be positioned in the center of the magnet and the examination will proceed. The MRI examination is made up of multiple series of images. Each series employs a different factor which will produce images that will allow for diagnosis. Following completion of the examination, you will be escorted out of the magnet area to collect your valuables. The images will now be available for the radiologist to review.

After the Test: Following completion of the MRI examination the patient is allowed to go home. There may be some minor pain following the procedure. This discomfort will usually not last for more than 24 hours and is commonly relieved by an over the counter anti-inflammatory preparation. It is advised that the patient not undergo heavy exercise involving the joint that was injected.

Factors Affecting the Test: There are multiple factors that may affect the test, this includes bleeding, an allergy to iodine, motion, and artifacts from metal from previous surgery.

Advantages: MRI arthrography can improve the diagnostic accuracy examination of the joints. First adding contrast to the joint distends the joint and improves visualization of the anatomy. Second, there is an increase accuracy in interpretation of selective studies. Finally, there is improvement in dialogue between the orthopaedic surgeon and the patient.

Disadvantages: MRI arthrography is expensive. In addition, it is a invasive procedure and there is a small exposure of radiation during the arthrogram.

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Computed Tomography (CT scan)

Computed tomography is similar to traditional x-ray, and in fact, employs the same principles. The major difference is that the spacial resolution using CT scanning is much greater than traditional radiography.

Purpose: We examine bony areas for fracture, fracture healing, bony alignment, infection (osteomyelitis), and bone tumors (either primary or metastatic). CT scanning can be helpful with surgical planning by employing multiplanar reformatting as well as supplying the data for 3D reconstruction.

How It Works: CT scanning is a specialized form of traditional x-ray. The x-ray tube is located within the gantry of the CT scanner instead of being fixed as in traditional x-ray. The x-ray tube spins around in a 3600 arc producing images at a single location from different points within the circular plane. The imaging data is sent back to a high-speed computer, which assembles all the information taken from the 3600 scan and produces a single image. The principles of CT are similar to radiology in that there are only four densities identified: air, fat, soft tissue, and metal.

Preparation: There is no specific preparation required for traditional musculoskeletal CT examinations. If there is a plaster or fiberglass cast, it is better to have the cast removed or split (cut in half but held together by an elastic bandage). If the cast is split it can be removed for the examination. This will help to improve resolution. Following the study, the splint can be re-applied. The patient will need to return to the orthopaedic surgeon following the exam for application of a more permanent cast.

If the patient has an allergy to medications such as iodine or shellfish, the technologist should be informed if intravenous contrast is a consideration. Also, if there is a history of renal disease, in this case should be removed. In this case contrast may be contraindicated. Also, if there is a possibility that the patient is pregnant this may be a contraindication for the CT examination.

Procedure: The patient is placed on the CT examining table and the area in question is identified using special markers. The patient is moved to the exact area of interest and imaging is performed beginning slightly above to just below this location. The patient may hear or see the x-ray tube spin around in 3600 course as the imaging is being performed. Occasionally, intravenous contrast may be given. This contrast is a traditional iodine based substance which helps demonstrate the vascularity of the structures in question.

Following the examination, the patient may go back to their normal routine. Images are interpreted by the radiologist and a report is sent to the referring physician.

Advantages: CT examination is fast and its increased spacial resolution as compared to traditional x-ray.

Disadvantages: The examination is expensive, and there is exposure to ionizing radiation. If the patient requires intravenous contrast, there is a possibility that there may be an allergic reaction.

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CT Arthrography

CT arthrography is similar to MRI arthrography. Contrast material is injected into a joint and coupled with an imaging modality that gives higher resolution. Instead of using the MRI machine a CT scanner is employed.

Purpose: To evaluate the structures in and around joints. The joints commonly examined include the shoulder, elbow, wrist, hip, knee, and ankle.

How it works: CT scanning is a specialized form of traditional x-ray. The x-ray tube is located within the gantry of CT scanner instead of being fixed as in traditional x-ray. The x-ray tube spins around in a 3600 arc producing images at a single location from different points within the circular plane. The imaging data is sent back to a high-speed computer, assembles all the information from the 3600 and produces a single image. The principles of CT are similar to radiology in that there are only four densities identified: air, fat, soft tissue, and metal.

Iodinated contrast is injected into the specific joint. If there is a tear in the cartilage or other structure associated with the joint, the contrast will migrate into the soft tissue or into a space that is not normally communicating with the joint.

Preparation: There is not specific preparation required. If the patient is on a blood thinner or aspirin, it would be advantages to discontinue this medication under the supervision of the referring physician. This is because bleeding is always a complication of any interventional procedure. Patient has allergies to medication, iodine, shell fish, or seafood, these factors should be discussed with the radiologist prior to the beginning of the procedure. Also, if there is a chance the patient may be pregnant, this may be a contraindication of the procedure.

Procedure: The arthrogram is performed under direct visualization using an x-ray camera or fluoroscope. The patient is brought into a traditional x-ray/fluoroscopy suite, and the patient is positioned on the table. The area is marked and the skin is washed with a cleansing solution such as betadine. Local anesthetic is given into the skin and into the underlying muscle. A special needle is used to enter the designated joint, such as a shoulder or knee. The position of the needle is confirmed to be intraarticular by injecting several cc's of iodinated contrast. Once the needle is in the joint a solution of iodinated contrast is injected. Sometimes, the radiologist may elect to do a double contrast arthrogram. In this case a second type of contrast, usually air, is injected along with the traditional contrast. Following the injection the patient is escorted to the CT scanner where the second part of the examination is performed. The patient is placed on the CT examining table and the area in question is identified using special markers. The patient is moved to the exact area of interest and imaging is performed beginning slightly above to just below this location. The patient may hear or see the x-ray tube spin around in 3600 course as the imaging is being performed. Following the examination, the patient is allowed to go home. There may be some minor pain following the procedure most commonly relieved by an antiinflammatory medication. The images are reviewed and the report is sent to the referring MD.

After the Test: Following completion of the MRI examination the patient is allowed to go home. There may be some minor pain following the procedure most commonly relieved by an over the counter anti-inflammatory medication. It is advised that the patient not undergo heavy exercise involving the joint that was injected

Factors Affecting the Test: Bleeding, allergy to iodine that may require special preparation, artifacts from metal from prior surgery, and finally the inability to inject contrast into joint because of scarring or other soft tissue abnormality.

Advantages: The examination is fast with high spacial resolution.

Disadvantages: The examination is expensive. There is exposure to ionizing radiation.

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CT Guided Bone Biopsy

Purpose: To obtain tissue from bone or surrounding soft tissue adjacent to the bone for histological diagnosis. This procedure frequently obviates the need for an open surgical biopsy.

How It Works: By using a special needle and employing CT guidance, a stereotactic approach can be used to obtain tissue.

Preparation: The patient is asked to discontinue eating solid food for six hours before the procedure. In addition, if the patient is taking any blood thinning agents like coumadin or aspirin, these drugs should be discontinued approximately five days prior to biopsy. This should be discussed with the patient's referring physician as to whether this may be safe to discontinue depending on the underlying medical condition. On the morning of the biopsy the patient is allowed to drink a small amount of clear liquids and take medication (no blood thinning agents) but not solid food.

Procedure: Following explanation of the procedure and obtaining informed consent, an intravenous catheter is placed in the arm. The examination is performed using conscious sedation which is intravenous medication or that allows the patient to remain comfortable during the procedure. This is not general anesthesia. The patient's vital signs and breathing are monitored by the diagnostic imaging nursing staff.

The area of interest is localized with the CT scanner and marked. The area is then prepped with a cleaning solution and draped with sterile sheets. Local anesthesia (lidocaine) is administered in addition to intravenous sedation. A series of specialized needles are employed and multiple biopsies of the bone, soft tissue, or a combination of each are obtained. The specimens are sent to surgical pathology, surgical cytology or both.

After the Test: Following the procedure, the area is washed and the bandages applied. By the time the patient leaves the CT scanning area, the patient is usually awake and is talkative. The patient is then transferred to a recovery area and observed for approximately one hour.

Complications from this procedure are commonly minor pain which is usually relieved by over the counter antiinflammatory medicine. Occasionally, stronger medication is required and a prescription will be given to the patient before being discharged. Other problems which may seen in any interventional procedure include infection and bleeding.

Following the procedure the patient may resume a normal diet, medication, and activities. If a blood thinner was discontinued is should be restarted under the guidance of the patient's primary physician usually on the morning after the biopsy procedure.

The processing of bone biopsies is slightly more complicated than a traditional soft tissue biopsy. The bone or calcium in the specimen must be removed before it can be placed on a slide for analysis. This usually takes an additional 24 - 36 hours. Therefore, the histological diagnosis cannot be ascertained until approximately 2-3 days following the procedure. The referring physician will call the patient with the results.

Advantages: The procedure of percutaneous biopsy can obviate the need for open excisional biopsy in selected cases. The excisional biopsy requires the patient to go to the operating room for a traditional surgical procedure. In the Yale experience, the percutaneous route has produced diagnostic results in the vast majority of patients.

Disadvantages: The procedure is invasive but not to the same extent as an open surgical biopsy. As with any interventional procedure, bleeding, infection, or reaction to the anesthesia may occur. These complications, although possible are infrequent. This is exposure to a small amount of ionizing radiation

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Joint Aspiration

Purpose: The large joints in are body like the shoulder, hip, and knee are synovial joints. This means that they are lined with synovial tissue which produces a viscus fluid that acts as a lubricant. For a number of reasons, it is sometimes necessary to examine this fluid which requires aspiration of the joint.

Preparation: There is no preparation required for this procedure.

Procedure: Following consent, the patient is placed on the x-ray (fluoroscopy) table and the area over the site of the puncture is marked. The area is washed and sterile towels are placed over the area of interest. A small injection of local anesthetic (lidocaine) is injected into the skin and underlying muscle. The anesthesia is carried down to the joint.

A special needle is used to enter the joint and fluid, if present, is aspirated. A small amount of iodinated contrast is injected to demonstrate that the tip of the needle was indeed intraarticular.

Following the aspiration, the needle is withdrawn. The area is washed and the bandage is placed over the puncture site. The patient is allowed to leave the department and continue on with their normal daily routine.

After the test: The synovial fluid is separated into small vials and sent to various laboratories where a number specific tests are performed. The typical test include analysis of the fluid for proteins and cells. In addition a small sample is sent to the microbiology laboratory for culture. Occasionally, a small amount of discomfort may occur which is normally relieved by an over the counter anti-inflammatory medicine.

The patient is usually seen by the referring physician, and the results are discussed.

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