Bone Marrow Imaging by Nuclear Medicine Technique

Bone marrow imaging in nuclear medicine is a rather infrequently performed study though it produces good quality images that can answer a variety of clinical questions.
Indications for exam:
a. Determine the functional capacity of bone marrow in anemic patients
b. Locate active sites for bone marrow biopsy
c. Assess enlargement of functional bone marrow space
d. Identify marrow replacement by primary or secondary tumors, thus helps in detecting micrometastasis in case of solid tumors. It is postulated that bone marrow metastasis occur early in soe cases like cancer breast before the skeletal mets occur.
Anatomy & Physiology
Physiologically active bone marrow is found in a limited number of sites in a normal adult. These sites include the: sternum, pelvis and vertebral column. Only in pathological conditions, when the bone marrow space is enlarged, do additional marrow sites throughout the rest of the skeleton become active.Since the bone marrow has a blood and lymphatic supply, metastatic disease can proliferate.

Radiopharmaceutical Information
• Type: Tc-99m sulfur nano colloid or a radioactive form of iron
• Adult dose: 10-15 mCi
• Delay time to imaging: 15 minutes to 1 hour
• Route of excretion: renal
• The liver receives the highest rads, followed by spleen then marrow
Since sulfur colloid contains particulate matter, it is phagocytized by the reticuloendothelial cells of the body (liver, spleen & marrow). This is its methods of dose uptake and incorporation of radiopharmaceutical agent at the site of interest.

Instrumentation
• Low energy high resolution collimator is used in the gamma camera.
• Energy setting: peaked on 140 keV with 20% window
• Acquisition type: whole body scan with slow scan speed or multiple static views of 100K per image
• There is no quantification study method yet developed in this examination.

Clinical Indications for Bone Marrow Imaging
• Abscesses & metastases: if large enough will present as focal areas of decreased radiopharmaceutical uptake, producing a radiopenic ("cold") area.
• Leukemia & lymphoma: can present with decreased bone marrow uptake or ectopic bone marrow visualization if compensatory mechanism is active
• Polycythemia vera: normal marrow pattern is seen along with additional sites typically non-active in the normal patient.