REF001 - Bone Scan

The purpose of this document is to assist clinicians in deciding on the appropriateness of a Nuclear Medicine bone scan and to give guidance on the mechanism of referral.

The bone scan a sensitive method for demonstrating disease in bone, often providing earlier diagnosis or demonstrating more lesions than are found on X-ray. It can be used to investigate a wide variety of conditions, both benign and malignant, in adults and children. It is a non-specific investigation and any lesion in bone such as fracture, infection, tumour or healing bone will show as an area of increased radiopharmaceutical accumulation. In many clinical situations, however, the anatomical distribution of the radiopharmaceutical combined with the clinical history or radiographs will suggest a specific diagnosis.

Phosphate analogues are now widely used for bone imaging, having a high localisation in bone and fairly rapid blood clearance from soft tissues. The radiopharmaceutical used locally is Tc^99m labelled disodium oxidronate (HDP). The uptake of radiopharmaceutical in bone is related to a number of factors, the most important of which are the blood supply and the rate of bone turnover. Other factors include the quantity of mineralised bone, capillary permeability and the fluid pressure within bone. The phosphates bind to bone first by adsorption on to the bone, followed by binding to the crystalline lattice and organic matrix. The bone scan therefore provides a functional display of skeletal activity. As functional change in bone occurs earlier than structural change, the bone scan, as stated above, will often detect abnormalities before they are seen on X-ray.

Delayed images are usually acquired between 2 and 4 hours after administration of the radiopharmaceutical. When infection of a bone or joint is suspected, or when an assessment of blood flow is required, a three phase investigation can be performed. This involves a dynamic flow study of the area of interest with rapid sequential images taken at the time of radiopharmaceutical administration. Dynamic images are followed by static images of the areas of interest at approximately 5 minutes after administration. These demonstrate the blood pool in normal soft tissue and any hyperaemic areas in bones, joints or soft tissue. Conventional delayed images are then acquired between 2 and 4 hours after administration.

• Any clinician holding a current valid medical qualification currently employed in Primary or Secondary care.

Referring clinicians are reminded of the requirement to avoid unnecessary exposure to ionising radiation. The investigation may already have been requested at this hospital or elsewhere and clinicians are asked to be particularly vigilant to ensure that their request is not a double request.

Requests will only be accepted if the diagnostic question fulfills one of the referral criteria below. Appropriate clinical information must be supplied to allow the investigation to be justified. It is not acceptable to simply request the investigation without appropriate clinical information.

Requests will be returned to the referrer if:

• The diagnostic question is unclear.
• The diagnostic question cannot be answered by the investigation.
• Insufficient clinical information is supplied to justify the investigation.

Requests should be submitted on the orange stripe NUCLEAR MEDICINE (ISOTOPE SCAN) request form. Patient details, Investigation required and Reason for Test/Diagnostic Question should be fully and appropriately completed and the form signed.

Primary Care referrals will be accepted on a standard X-ray request form provided that the same details as required by the orange stripe form are completed. Primary Care are encouraged to use the orange striped form which can be supplied by the Medical Physics Department.

Sufficient clinical information must be provided to justify the investigation proceeding.

The clinical indications for a bone scan are continually being extended, but fall into the categories as detailed below.