Mammoscintigraphy

Anatomy and Physiology

Normal distribution of technetium 99m sestamibi (the most commonly used radiopharmaceutical for scintimammography) is in the salivary glands, thyroid, myocardium, liver, and gallbladder.

Any uptake of radiopharmaceutical greater than the average breast parenchyma is suspicious for malignancy. If the breast demonstrates mild, homogenous uptake of the radiopharmaceutical, it is considered a normal study. Patchy, widespread uptake likely is not indicative of malignancy. Evaluation of the axilla is important for interpreting potential metastasis to axillary lymph nodes in the presence of an ipsilateral focal area of increased uptake suggesting primary malignancy. Axillary folds will demonstrate increased uptake as an artifact and should be considered normal but can be a pitfall, and lateral imaging should be used to identify its superficial location and linear appearance.[6]

Indications

Indications for scintimammography are debated given that MRI is currently the more preferred modality for similar indications; however, the most commonly stated reasons scintimammography is performed include equivocal, suspicious, or difficult to interpret mammograms and potential multifocal breast cancer. Additionally, patients with breast implants, axillary lymph node metastasis of an adenocarcinoma of unknown primary origin, and monitoring response to neoadjuvant chemotherapy.[7][8][9][10]

Contraindications

Contraindications for scintimammography are also currently being debated, with most of these being relative contraindications. Pregnant or lactating women would pose a high risk for the fetus and/or infant regarding radiation exposure. Scintimammography should not be performed if there is a history of recent surgical intervention, including cyst aspiration, fine needle aspiration, core needle biopsy, and excisional biopsy, with the suggestion to wait 2 weeks for minor procedures and up to six weeks for major procedures. Appropriate delay in the examination is recommended to minimize the chances of false positives from increased uptake in the post-surgical reactive tissues. Examination during menses should also be avoided, as well as hypersensitivity to technetium 99m.[11]

Equipment

A standard scintillation camera with a low-energy/high-energy collimator is used. A symmetric 10% energy window is used, centered over the 140 keV photopeak of technetium 99m.[11]

Personnel

Radiologists, nuclear medicine physicians, nuclear medicine technicians, cyclotron engineers/workers, and scheduling departments must coordinate activity to set up and obtain a scintimammogram. All members of the interprofessional healthcare team play a vital role in carrying out the task.

Preparation

No specific preparation is needed for the patient to have a scintimammogram. A nuclear medicine technologist will be an asset to assist in the explanation and execution of the examination. It should be ensured that the patient is capable of lying prone on a hard surface with the arms extended above the head before the procedure is started. The patient should wear a hospital gown and remove all clothing and jewelry.

Quality control should be performed according to the general guidelines issued by the Society of Nuclear Medicine for the scintillation camera.[11]

Technique or Treatment

Imaging can be obtained in either planar and/or single-photon emission computed tomography. Intravenous injection with an indwelling catheter or butterfly needle of 20 to 30 mCi of technetium 99m into a vein of the upper extremity should be contralateral to the breast of concern. If there are suspicious bilateral findings, the lower extremity is then injected. Approximately 10 mL of saline flush should follow.

Prone positioning is appropriate with the non-pathological breast compressed against the table to prevent the dependent breast from artifacts from the contralateral breast. The arms are raised over the head with the head turned away from the detector to minimize artifacts. The detector is placed against the patient.

The patient should be imaged 5 to 10 minutes after injection. Planar images to be obtained include prone lateral (including the breast, axilla, and anterior chest wall), prone posterior oblique, and anterior upright/supine chest (includes bilateral breasts and axillae). If a marker is desired, it should be placed once the breast is in the proper position; otherwise, the abnormality could change relative to the marker.

The breast tissue is near myocardial tissue, which is an organ that takes up technetium 99m, so post-procession count subtraction should be obtained.[11]

Complications

The procedure is relatively non-invasive with few adverse effects; however, potential complications could include extravasation of radiopharmaceuticals and allergic reaction to radiopharmaceuticals. Extravasation of technetium 99m has not been shown to cause significant harmful effects to the tissue involved, and usually, surgical intervention would not be necessary. Allergic reactions to radiopharmaceuticals are rare, but if they happen or are at risk of occurring, appropriate steps are given by the American College of Radiology, which includes preparation with corticosteroids and antihistamines as well as emergent medications pending the development of any symptoms; these would include epinephrine and labetalol.[12]

Clinical Significance

The main purpose of scintimammography is to increase the positive predictive value of breast cancer detection with imaging to decrease the overall cost and improve the patient experience by minimizing the number of negative breast biopsies. Currently, scintimammography is not commonly used because of the prevalence of MRI for such examinations, as stated above. However, if additional research and discussion are performed to support its efficacy and use, it could be a valuable asset for the breast imaging world.[7][13][9]

Enhancing Healthcare Team Outcomes

Scintimammography is a diagnostic imaging modality using radiopharmaceuticals to identify breast malignancies. With limited complications, allergic reaction to radiopharmaceuticals, and extravasation of radiopharmaceuticals, the most effective way of enhancing healthcare team outcomes is through identifying every step of the process and assigning a role to each team member. Prior to the patient arriving at the hospital or clinic for their examination, the following should be done:

• Appropriate scheduling should be provided to the patient to allow for optimal patient satisfaction.
• Screening for a history of recent surgeries, menstrual cycle, recent imaging with radiopharmaceuticals, history of contrast/radiopharmaceutical reactions, and personal medical history should be administered. Appropriate preparation for the patient should be overseen by the radiologist.
• The nuclear medicine technician should perform quality control according to the general guidelines by the Society of Nuclear Medicine on the scintillation camera.
• The radiologist should review the imaging to understand the case better and ensure that the study meets the appropriate criteria.
• Radiopharmaceuticals of choice should be prepared and shipped within the appropriate timeframe to prevent radioactive decay.

When these interprofessional roles have been assigned and are accomplished without interruption, the coordinated efforts of the entire interprofessional healthcare team, including the patient, demonstrate an overall better experience and more positive outcomes. [Level 5]