SKELETAL RADIONUCLIDE IMAGING

II

Dr. Hussein FarghalyNuclear Medicine

ConsultantPSMMC

CONTENTS

• Bone and BM physiology & anatomy

• Bone scan • Radiopharmaceutical,

• preparation,

• uptake and pharmacokinetics

• dosimetry,

• protocols,

• normal and altered distribution

• Clinical indication and Skeletal pathology

• Bone Marrow scan

Bone scan Radiopharmaceutical

• Preparation

• uptake and pharmacokinetics

• dosimetry

• protocols

• normal and altered distribution

Radiopharmaceutical • Therefore a radiopharmaceutical is typically made of two components, the Therefore a radiopharmaceutical is typically made of two components, the

radionuclide and the chemical compound radionuclide and the chemical compound to which it is bound. to which it is bound.

• Since radiopharmaceuticals are used to study body functions, it is important that they have no Since radiopharmaceuticals are used to study body functions, it is important that they have no pharmacological or toxicological effects which may interfere with the organ function under study. pharmacological or toxicological effects which may interfere with the organ function under study. Therefore the pharmaceutical is administered in Therefore the pharmaceutical is administered in extremely small amounts (10extremely small amounts (10-9-9 g). g).

• An ideal radiopharmaceutical for skeletal scintigraphy must be inexpensive, remain stable, rapidly localize to bone, quickly clear from the background soft tissues, and have favorable imaging and dosimetry characteristics.

• These parameters were essentially met in the 1970s when technetium-99m,already desirable for gamma camera imaging studies, was combined with members of the phosphate family.

History of Bone Radiotracer

• Radium-226, 1920

• Phosphorus-32, radioisotopes of calcium, several rare earth elements, and isotopes of gallium, barium, samarium, and strontium.

• (F-18) is an analog of the hydroxyl ion found in calcium hydroxyapatite and avidly localizes to bone. It was the agent of choice for skeletal scintigraphy until the advent of the :

• Tc-99m phosphonates in the 1970s.

Other substances that can be used but I will only mention in passing are: gallium,

thallium,

indium & Tc-99m labeled leucocytes and polyclonal immunoglobulins labeled with technetium.

Technetium-99m phosphate family• These radiopharmaceuticals are classified by the type of phosphate bond. The first of

these agents, pyrophosphates and then the longer-chain polyphosphates, were

soon replaced by the diphosphonates .

The diphosphonates are more stable in the body and have better background clearance than pyrophosphates or polyphosphates.

The diphosphonate agents include Tc-99m hydroxyethylidene diphosphonate (Tc-99m HEDP),Tc-99m hydroxymethylene diphosphonate (Tc-99m HMDP or HDP), and Tc-99m methylene diphosphonate (Tc-99m MDP).

The ability of each diphosphonate to detect lesions has been studied. Although some differences are present,Tc-99m MDP and Tc-99m HDP are both excellent agents.

PREPARARTION

Radiopharmaceutical quality control:

• Visual Inspection of Product

- Visual inspection of the compounded radiopharmaceutical shall be conducted to ensure the absence of foreign matter and also to establish product identity by confirming that

(1)a liquid product is a solution, a colloid, or a suspension

(2) a solid product has defined properties that identify it.

• Assessment of Radioactivity

-The amount of radioactivity in each compounded radiopharmaceutical should be verified and documented prior to dispensing, using a proper standardized radionuclide (dose) calibrator.

Radiopharmaceutical quality control:

• Radionuclidic Purity

- Radionuclidic purity can be determined with the use of a suitable counting device

-The gamma-ray spectrum, should not be significantly different from that of a standardized solution of the radionuclide.

• Radiochemical purity

- Radiochemical purity is assessed by a variety of analytical techniques such as:

- liquid chromatography - paper chromatography

- thin-layer chromatography - electrophoresis

the distribution of radioactivity on the chromatogram is

determined.

Radiopharmaceutical quality control:• LabellingThe label on the outer package should include:• a statement that the product is radioactive or the international

symbol for radioactivity• the name of the radiopharmaceutical preparation;• the preparation is for diagnostic or for therapeutic use;• the route of administration;• the total radioactivity present (for example, in MBq per ml of

the solution) • the expiry date • the batch (lot) number • for solutions, the total volume;• any special storage requirements with respect to temperature

and light;• the name and concentration of any added microbial

preservative

Mechanisms of Localization andPharmacokinetics

• After intravenous injection,Tc-99m MDP rapidly distributes into the extracellular fluid and is quickly taken up into the bone.

• Tc-99m MDP accumulates controlled by

• primarily in relation to osteogenic activity levels,

• amount of blood flow plays a part.

• Activity is much higher in areas of active bone formation compared with mature bone.

• Tc-99m MDP binding occurs by chemoadsorption in the hydroxyapatite mineral component of the osseous matrix.

• Uptake in areas of amorphous calcium phosphate may account for Tc-99m MDP uptake in sites outside the bone, such as dystrophic soft tissue ossification.

Mechanisms of Localization andPharmacokinetics

• Approximately 50% of the dose is localized to the bone with the remainder excreted by the kidneys.

• Although peak bone uptake occurs approximately 1 hour after injection, highest target-to-background ratios are seen after 6–12 hours. This must be balanced with the relatively short 6-hour half-life of Tc-99m and patient convenience. Therefore, images are typically taken 2–4 hours after injection.

• Serum radiotracer levels at this time are down to 3–5% of the injected dose in patients with normal renal function.

• It should be noted that the half-life of Tc-99m effectively limits imaging to within approximately 24 hours of injection.

• Decreased localization is seen in areas of reduced or absent blood flow or infarction. Diminished uptake is also seen in areas of severe destruction that can occur in

• some very aggressive metastasis

Dosimetry• The radiation dose to the bladder wall,

ovaries, and testes depends on the frequency of voiding.

• The dosimetry provided assumes a 2-hour voiding cycle.

• Significantly higher doses result if voiding is infrequent.

• Radiopharmaceuticals are administered to pregnant women only if clearly needed on a risk-versus-benefit basis.

• Tc-99m is excreted in breast milk so breastfeeding should be stopped for 24 hours

Normal Bone Scan1. Areas with normally increased activity

include: acromioclavicular joints, sternoclavicular joints, scapular tips, costochondral junctions, sacroiliac joints, lower neck, sternum, renal pelves and bladder

2. Pediatric patients: growth centers and cranial sutures

3. Pitfalls- Patient rotation- Urine retained in calyx may overlie lower

rib- Urine contamination- Belt buckles, earrings, necklaces, and the

like frequently create cold defects- Recent dental procedures- Radiopharmaceutical problems: breakdown

of tag leading to free pertechnetate causes activity in thyroid and GI tract

  Anterior (left) and posterior (right) whole-body bone scintigrams obtained in a child demonstrate normal anatomy. Note the increased activity in the physes of the long bones and

in the hematopoietically active facial bones

Normal Childe Bone Scan

 (a) Anterior bone scintigram shows discrete focal activity in the left maxilla (arrowhead) due to a dental process and heart-shaped activity in the anterior neck (arrow) representing the

thyroid cartilage, both of which are normal variants.

 Myocardial uptake in a patient with long-standing congestive heart failure.

 Extra osseous uptakeFree Tc-99m. Colonic Activity

Planner SPECT- coronal

Artifact from an implanted defibrillator

Diffuse hepatic metastasis

Iron Therapy and overload