SNMMI Procedure Standard for Bone Scintigraphy 4.0

A. Physician

Bone scintigraphy should be performed by, or under the supervision of, a physician specialized in nuclear medicine and certified by the appropriate accrediting boards.

B. Technologist

Bone scintigraphy should be performed by a qualified registered or certified nuclear medicine technologist. Refer to the Performance Responsibility and Guidelines for the Nuclear Medicine Technologist for further details. In Europe, refer to the European Qualifications Framework level 6: EANM benchmark document on nuclear medicine technologists’ competencies.

C. Medical Physicist

The medical physicist should be involved in the aspects of protocol/image acquisition and processing as necessary. In addition, acquisition should be performed as recommended by the manufacturer.

A. Study requisition

The requisition should include all clinical information about the patient necessary for correct coding of the study. The requisition should also indicate the ability of the patient to cooperate, if there is need for mild sedation or analgesia, and whether the patient needs to be accompanied by a guardian. Any medications the patient is currently taking should also be noted. Any recent trauma or surgery is also useful information to include.

B. Patient preparation and precautions

1. Pre-arrival and patient instructions

  The rationale for and details of the procedure should be explained to the patient in advance. Any questions should be answered, and if available, written information provided.

  Unless contraindicated, patients should be well-hydrated and drink two or more 8-ounce glasses of water between the time of radiopharmaceutical injection and the time of delayed imaging. In order to promote excretion and minimize radiation exposure, patients should also drink additional fluids and void frequently for at least 24 h after the injection. In addition, patients should empty their bladder frequently between the injection and delayed imaging, including immediately before the scan.

2. Information pertinent to the procedure

  Relevant clinical information should be obtained, including current symptoms; pertinent physical findings; history of fracture/trauma, osteomyelitis, cellulitis, edema, arthritis, neoplasm, or metabolic bone disease; and any functional limitations. Information on any relevant recent imaging studies should also be obtained, including scintigraphic imaging, especially bone scans and imaging with radiopharmaceuticals such as ¹⁸F-NaF, ¹⁸F-FDG, ¹³¹I, ⁶⁷Ga, ¹¹¹In, or ^99mTc-sulfur colloid, and anatomic imaging studies such as conventional radiography, CT, or MRI.

  If the patient has received any prior therapy that may affect the results of bone scintigraphy (e.g., antibiotics, corticosteroids, chemotherapy, radiation therapy, diphosphonates, and/or iron therapy), this should be noted, as should any history (and the date) of orthopedic surgery (including the type, presence, and location of implants and any complications) or non-orthopedic surgery (e.g., ileal conduit). Anatomic or functional abnormalities of the urinary tract should also be noted as well as any relevant laboratory results (e.g., prostate-specific antigen in patients with prostate cancer).

3. Precautions

  The technologist should determine whether any female patient of childbearing age is pregnant, and if so, should confer with the ordering/requesting team service to confirm that the procedure is medically necessary and cannot be deferred until after pregnancy and breastfeeding. Per the International Commission on Radiological Protection, ^99mTc-labeled radiopharmaceuticals do not require any change in breastfeeding (unless ^99mTc-NaO₄ is present). Nevertheless, it may be recommended that the patient delay breastfeeding for a minimum of 4 h after receiving a ^99mTc-labeled radiopharmaceutical, and many institutions have the patient delay breastfeeding for 24 h.

  Drugs that may interfere with bone scintigraphy include aluminum-containing compounds, corticosteroids, iron, methotrexate, nifedipine, hematopoietic growth factors, androgen deprivation therapy drugs, estrogens, bisphosphonates, those that interfere with osteoblastic function, nephrotoxic chemotherapy, and E-amino caproic acid. Bone scintigraphy may still be performed while the patient is taking any of these drugs if clinically indicated. However, if a prior bone scan was thought to be non-diagnostic because of interference from one of these medications, the scan should be deferred until the medication can be stopped long enough to minimize interference.

C. Radiopharmaceuticals

Several ^99mTc-labeled radiopharmaceuticals from the bisphosphonate family are available for bone scintigraphy. These include methylene diphosphonate, hydroxyethylene diphosphonate, and 2,3-dicarboxypropane-1,1-diphosphonate.

1. Characteristics

  ^99mTc decay is by isomeric transition with emission of 140.5-keV γ-rays. The half-life is 6.02 h. ^99mTc-labeled radiopharmaceuticals attach to the bone surface by chemisorption (attachment to hydroxyapatite crystals in bone and calcium crystals in mitochondria). Approximately 50%–60% of diphosphonate tracers attach to bone by 3–4 h after administration. Uptake of diphosphonate tracers in bone is enhanced by increased osteoblastic activity and increased blood flow. The primary excretion route is renal with approximately 70% clearance by 6 h. Clearance is typically delayed in patients with renal impairment.

2. Administration

  Administration is typically intravenous but can also be performed through an indwelling intravenous catheter or butterfly needle if necessary.

  The administered activity is usually 500–1,110 MBq (∼13–30 mCi) for adults but may be increased to 11–13 MBq/kg (300–350 μCi/kg) for markedly obese adults. For children, the administered activity is based on body weight according to the guidelines of the European Association of Nuclear Medicine (EANM)/SNMMI Pediatric Dosage Harmonization Working Group. The typical pediatric dose is 170–210 MBq (∼4–6 mCi), with a minimum of 20–40 MBq (0.5–1.0 mCi) and a maximum not exceeding the maximum for a healthy adult.

  Bone radiopharmaceuticals are subject to oxidation. Care should be taken to avoid introducing air into the vial and/or syringe. Quality control testing should be performed before administration (see the SNMMI Procedure Standard for the Use of Radiopharmaceuticals).

D. Protocol/image acquisition and processing

The energy window should be centered at 140 keV with a window width of between 15% and 20%.

1. Phase 1 images

  If flow images are acquired, the camera should be positioned over the region of interest before radiopharmaceutical injection. The acquisition computer should be programmed to acquire approximately 30–60 images at 1–3 s/frame. When digital images are acquired, blood flow images may be obtained in a 64 × 64 or greater matrix.

2. Phase 2 images

  Blood pool images should be acquired for approximately 3–5 min/image immediately after the flow phase and within 10 min after injection of the tracer. After 10 min, activity may appear in the skeleton. Blood pool images are usually obtained in a 128 × 128 or greater matrix and with a count density of approximately 300,000 counts per image (150,000–200,000 counts per image may be adequate for the extremities).

3. Phase 3 images

  Routine delayed images are usually obtained from 2 to 4 h after injection of the tracer to allow it to clear from the soft tissues.

  When whole-body scanning is used for routine delayed imaging, the count rate (usually of the anterior chest) should be determined before image acquisition, and the scanning speed should be adjusted so that the images contain more than 1.5 million total counts. The views are anterior and posterior and are usually obtained in a 256 × 1,024 or greater matrix. Whole-body scanning can be accomplished with multiple overlapping images or with continuous images.

  When spot views are used as the primary method of acquiring the routine delayed images, the areas covered by the spot views must overlap so that the entire skeleton is imaged. The recommended counts per region are 500,000–1 million for the thorax and abdomen, 250,000–400,000 for the skull and large joints, and 150,000–250,000 for distal extremities. More counts should be obtained when the field of view is larger. A 128 × 128 or 256 × 256 matrix can be used.

  An additional delay in imaging (6- to 24-h) will result in a higher target-to-background ratio and may permit better evaluation of the pelvis if it was obscured by bladder activity on the routine delayed images. An additional delay may also be particularly helpful in patients with renal insufficiency or urinary retention.

  A pinhole collimator may be used if very high-resolution images of a specific area are necessary. This use is more common in imaging of infants, children, and small structures. Approximately 75,000–100,000 counts should be obtained for pinhole-collimator views. Zoom magnification or a converging collimator may also be used to improve visualization.

  Other views (e.g., lateral, oblique, or tangential) and special views (e.g., frog-leg views of the hips or sitting-on-detector [caudal] views of the pelvis) may be obtained when necessary.

4. Pelvic images/interventions

  The pelvis can be difficult to evaluate when there is overlying bladder activity. In patients with pelvic symptoms, one or more of the following additional views may better evaluate the pelvis: images repeated immediately after voiding, sitting-on-detector (caudal) or oblique images, lateral images, 24-h delayed images, and images acquired immediately after bladder catheterization (which should be reserved for patients in whom visualization of the pelvis is essential).

  Single or multiple rapid (5–10 min/acquisition) SPECT images are preferred to avoid artifacts caused by changes in bladder activity. Bladder artifacts are exaggerated in the plane in which the SPECT acquisition begins and ends. Beginning a dual-head SPECT acquisition with the camera heads in the left and right lateral positions—or a single-head acquisition with the camera head in the posterior position—will help reduce bladder-filling artifact.

5. SPECT and SPECT/CT

  The increased contrast and diagnostic sensitivity and specificity of SPECT and SPECT/CT may help to better characterize the presence, location, and extent of disease in some patients. The acquisition should be performed as recommended by the camera manufacturer.

  Typical SPECT acquisition and processing parameters for a dual-head γ-camera are a 180° detector head orientation, a 360° circular orbit, 60–120 stops, a 64 × 64 or greater matrix, and 10–40 s/stop. An equivalent total number of counts should be acquired if continuous acquisition is used. Three-dimensional iterative ordered-subsets expectation maximization is the typical reconstruction algorithm, with typically 3–5 iterations and 8–10 subsets. Corrections are made for attenuation, scatter, and resolution recovery. Postprocessing usually includes application of a gaussian filter (width at half maximum, 4–10 mm) or a Butterworth filter (conventional parameters of 10.0.5).

  In SPECT/CT, the CT portion is for anatomic localization/attenuation correction and is performed before the SPECT portion using a multi-slice spiral or flat-panel/cone-beam CT scanner (currently up to 64 slices) with a low milliampere-seconds setting to decrease the patient radiation dose. The recommended SPECT parameters are the same as above. The CT parameters typically include a 512 × 512 matrix, a tube voltage of 80–130 kV, an intensity–time product of 2.5–300 mAs (depending on the anatomy being imaged), and application of a high-resolution filter to the final image. A single SPECT/CT field of view is usually 40 cm, and several separate or contiguous fields of view can be used. Fused 3-dimensional SPECT/CT images are usually displayed as 2-dimensional orthogonal (axial, coronal, and sagittal) and maximum-intensity projections.

E. Interpretation criteria

Bone scans are sensitive for detecting skeletal disease but with relatively low specificity, and these studies must be interpreted in light of other information. Reported bone scintigraphy findings should narrow the differential diagnosis as much as possible, and a further, more definitive study should be recommended if needed or if the differential diagnosis is broad. Information that will help in the interpretation includes the patient’s history and the results of physical examination, other tests, and findings from previous imaging studies.

An increase in radiopharmaceutical uptake, compared with normal bone, indicates increased osteoblastic activity. The differential diagnosis is long but can be narrowed in light of the pattern of uptake (focal or diffuse), location, and number of findings.

A decrease in uptake intensity or number of abnormalities in comparison with a previous study often indicates improvement and may be secondary to therapy (e.g., radiation or chemotherapy). On the other hand, an increase in uptake intensity or number of abnormalities may indicate progression of disease or a flare response to therapy, caused by increased osteoblastic activity at sites of bone repair.

Focal decreased uptake (i.e., focal area of photopenia) without adjacent increased activity is often caused by benign conditions such as attenuation, artifacts, and absence of bone (e.g., surgical resection). There are some cases where decreased uptake can also represent metastatic disease.

Diffuse increased soft-tissue uptake can be caused by renal failure, dehydration, a shortened interval between injection and imaging, post-trauma, or use of the wrong energy window for image acquisition. Focal increased soft-tissue uptake can be caused by localized infection or inflammation, trauma, infarction, and soft-tissue metastasis, particularly from mucinous primary lesions. Diffuse decreased soft-tissue uptake can reflect a superscan (diffusely increased uptake in bone) or result from a prolonged interval between injection and imaging (focal or diffuse uptake).

Interpretation errors may be caused by urinary contamination or diversion reservoirs; injection artifacts; prosthetic implants, radiographic contrast material, or other attenuating artifacts that might obscure normal structures; homogeneously-increased bony activity (e.g., a superscan); patient motion; increased collimator-to-patient distance; imaging too soon after injection before optimal clearance of the tracer from soft tissues; and restraint artifacts caused by soft-tissue compression. Of note, the technologist should note when there is possible radioactive urine contamination, clean the area with soap and water, and then repeat the examination without contaminated clothing.

Additional sources of interpretation error include prior administration of a higher-energy radionuclide (¹³¹I, ⁶⁷Ga,¹¹¹In) or of a ^99mTc tracer that accumulates in an organ that may obscure or confound skeletal activity; radioactivity extraneous to the patient; incomplete imaging of the entire bony skeleton; radiopharmaceutical degradation; changes in bladder activity during pelvic SPECT; purely lytic lesions; pelvic lesions obscured by bladder activity; renal failure; and myositis ossificans.

A. Indications

The report should briefly summarize the reason for the examination, the clinical problem, any pertinent medical or surgical history, the results of any relevant laboratory tests or prior imaging studies, and any treatments that may interfere with bone uptake.

B. Technique

The report should include the nonproprietary name of the radiolabeled bisphosphonate and describe the injection site and scanning protocol. If the technologist has injected the patient, this should be documented, including the dose, time, location, and whether the injection was uncomplicated. The scanning protocol should describe any of the following that are used: flow images, blood pool images, delayed images, SPECT or SPECT/CT images (the radiation dose from the CT portion should be stated), and additional intervention images.

C. Findings

The report should include the location and character of any abnormal uptake (abnormally increased, abnormally decreased, abnormal bony or soft-tissue pattern); a comparison with the results of prior imaging studies (if pertinent or available; this comparison—or notation that prior studies are not available—is a quality measure of the Physician Quality Reporting System); and any pertinent additional CT findings (if CT was performed with SPECT).

D. Impression

The impression should include conclusions, diagnoses, or differential diagnoses to answer questions posed by the referring clinician or team, any recommendations for further work-up, and an indication to contact the referring physician or service per local radiologic communication requirements (to include the contact information).