SKELETAL RADIONUCLIDE IMAGING II

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SKELETAL RADIONUCLIDE IMAGING II

• Dr. Hussein Farghaly
• Nuclear Medicine Consultant
• PSMMC

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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

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Bone scan Radiopharmaceutical

• Preparation
• uptake and pharmacokinetics
• dosimetry
• protocols
• normal and altered distribution

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Radiopharmaceutical

• Therefore a radiopharmaceutical is typically made
  of two components, the radionuclide and the
  chemical compound to which it is bound.
• 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. Therefore the pharmaceutical is
  administered in extremely small amounts (10-9 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.

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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.

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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.
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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.

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PREPARARTION
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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
• a liquid product is a solution, a colloid, or a
  suspension
• 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.

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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.

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Radiopharmaceutical quality control

• Labelling
• The 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

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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.

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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 612 hours. This must be
  balanced with the relatively short 6-hour
  half-life of Tc-99m and patient convenience.
  Therefore, images are typically taken 24 hours
  after injection.
• Serum radiotracer levels at this time are down to
  35 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

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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

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Normal Bone Scan
1. 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
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Normal Childe Bone Scan
  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
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 (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.
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 Myocardial uptake in a patient with
long-standing congestive heart failure.
 Extra osseous uptake Free Tc-99m.
Colonic Activity
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Artifact from an implanted defibrillator
Planner
SPECT- coronal
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Diffuse hepatic metastasis
Iron Therapy and overload