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Jiraporn SriprapapornSiriraj Hospital

Bone Scanfor MSc

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BONE SCAN• Introduction

– Definition– Other names– Advantages vs disadvantages

• Anatomy• Techniques

– Radiopharmaceutical– Mechanism of uptake– Imaging Technique

• Interpretation of bone scan• Clinical applications

http://www.med.nyu.edu/patientcare/library/article.html?ChunkIID=28679

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Definition

• A bone scan is a test that detects areas of increased or decreased bone activity by injecting a certain radiopharmaceutical ie. Tc-99m MDP.

• These may indicate bone injury or disease.

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Other names

• Radionuclide bone scan or • Bone scintigraphy

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Bone Scan Advantages Disadvantages

• Whole-body evaluation in one test/ same rad exposure.

• Low radiation exposure

• Sensitive evaluation

• Needs radiopharms & gamma camera not widely available

• Radiation exists

• Low specificity

• Cost is not so low.

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Skeleton

• Axial skeleton [head and trunk]– Skull– Thorax (ribs & sternum), – Spines (includes sacrum & coccyx)

• Appendicular skeleton– Shoulder girdle: clavicle & scapula– Arm, Hand– Pelvic girdle– Leg, Foot

Axial skeleton

Appendicular skeleton

http://anatowiki.wetpaint.com/page/Appendicular+skeleton

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Appendicular skeleton1. Shoulder girdle: clavicle & scapula2. Arm3. Hand4. Pelvic girdle5. Leg6. Foot 1. Sacrum

2. Ilium3. Ischium4. Pubic bone5. Pubic symphysis6. Acetabulum7. Obturator foramen8. Coccyx

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Skeleton• Axial Skeleton - forms the longitudinal axis of the body, it

has 80 bones, roughly 40% of the bones in the human body. Components of the axial skeleton :-The skull (8 cranial bones and 14 facial bones) -Bone assoicated with the skill (6 auditory ossicles and the hyoid bone)-The thoracic cage (the sternum and 24 ribs) -The vertebral column (24 vertebrae, the sacrum, and the coccyx)

• Appendicular Skeleton - consistes 126 bones, include the bones of the limbs and the pectoral and pelvic girdles that attach the limbs to the trunk.

•Read more: http://wiki.answers.com/Q/What_is_the_difference_between_the_axial_and_the_appendicular_skeleton#ixzz23TOla6BB

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Radiopharmaceuticals• Bone-seeking agents are

analogs of calcium, OK group, phosphates.

• The most widely used Rpharm is Tc-99m labeled diphosphonates; Tc-99m Methylene diphosphonate (Tc-99m MDP), Tc-99m Medronate

• Diphosphonates contains organic P-C-P bonds.[stable > P-O-P bond in pyrophosphate]

Tc-99m MDP

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Tc-99m MDP

• Labelling yield: > 95%, avoid injecting airinto the vial oxidation of Tc oxidized Tc poor tagging of phosphates

• Used within 4 hrs after prep ( free 99mTcO4-) – thyroid & gastric activity

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Tc-99m MDP

• Rapid renal clearance• High target/bcg ration within 2-3 hrs. with

50-60% of the injected activity localizing in bone (max sk uptake at 5 hrs)

• Tbio = 24 hrs• Deposition: by chemisorption ion the bone

surface concentrate in mineral phase of bone; 2/3 crystalline hydroxyapatite, 1/3 noncrystalline Ca3(PO4)2

Essentials of NM Imaging

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Renal Impairment

• Increased soft tissue activity• Poor image quality• Delayed excretion• Higher rad exposure due to retained high

activity

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Pathophysiology

Tc-99m MDP uptake depends on osteoblastand osteoclast activity.

• Increased uptake*- osteoblastic activity present

• Decreased uptake, pure lytic lesion-osteoclast activity

Krasnow AZ, SNM 1997

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Possible Mechanism of Increased Uptake

• Increased blood flow• Increased osteoid formation• Increased mineralization of osteoid• Interrupted sympathetic nerve supply

Page 244 Essentials NM

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Instrument

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Imaging Acquisition

• Routine whole-body bone scan

• 3-phase bone scan imaging

• SPECT & SPECT/CT imaging

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Technique of Bone Scan• Preparation: None• Injection of Tc-99m 20-25

mCi IV, good hydration afterwards & frequent voiding

• Wait for about 3 hrs to start imaging, avoid contamination

• Empty bladder prior to scanning

• Change the cloth and remove things likely cause artifact.

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Poor image quality

• Renal impairment• Decreased cardiac output• Dehydration• Extravasation of the radiopharamceutical• Aging

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Routine Bone Scan Imaging

• Whole-body planar imaging in anterior and posterior projection

• Routine static skull images in lateral views. (Siriraj)

• Additional static images if required eg. oblique or additional spot views (squat view)

ANT POST

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Interpretation

• Lytic lesions must cause at least 30%-50% demineralization to be visible by radiography.

• Bone scan is much more sensitive in detecting metastatic lesions in majority of cancers.

• Results– Normal-

symmetrical– Abnormal

• Increased uptake

• Decreased uptake

• Mixed ANT POSTANT POST

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Normal Bone Scan in Children

A

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False negative bone scan are high in …

• Multiple myeloma • Renal cell carcinoma • Thyroid carcinoma • Eosinophilic granuloma • Neuroblastoma• Highly aggressive anaplastic tumors • Reticulum cell sarcoma

http://roentgenrayreader.blogspot.com/2010/07/metastatic-disease-skeletal-surveys-and.html

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False positive bone scan• Contamination• Physiologic activity eg. urine along urinary tract.• FP bone scan is also high when a single lesion is seen. • In patients with known malignancy and no benign radiographic

explanation for a bone scan lesion, additional workup is necessary. STATS• A single spinal lesion on bone scan has a 10%-20% chance of

representing a metastatic focus. • A single rib lesion on bone scan has a 10% chance of representing a

metastatic focus. Lesions in consecutive ribs are almost always traumatic in origin. Lesions in nonconsecutive ribs have a high chance of representing metastatic disease.

• A single sternal lesion on bone scan in a patient with breast cancer, on the other hand, has an 80% chance of representing a metastatic focus.

• In the case of prostate cancer, PSA level < 10 μg/L is a good predictor of a negative bone scan.

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Phase 1; Vascular phase: 60 s dynamic immediately pi.Phase 2; Soft-tissue (blood-pool) phase: 5 min pi.Phase 3; Delayed (bone) phase: 3 hr pi.

Indications:•• InfectionInfection:: DDx acute osteomyelitis vs cellulitisDDx acute osteomyelitis vs cellulitis•• Avascular necrosisAvascular necrosis•• TumorsTumors:: primary tumorprimary tumor•• OthersOthers

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Clinical Applications

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Clinical Applications• Neoplastic disease:-Bone metastasis***

– Staging for malignancies that have high incidence of bone metastasis eg. cancers of prostate, breast, lung, neuroblastoma.

– Unexplained bone pain in a patient with known malignancy (neg X-ray)

– Unexplained bone pain in a patient with no history of malignancy.

• Trauma: Fracture/ Stress injuries (eg, stress fracture, shin splints), battered child

• Infection (osteomyelitis)• Avascular necrosis• Arthritis-Degenerative changes• Metabolic disorders (eg, Paget’s Disease, rickets)• To guide for bone biopsy or surgery• Others

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Degenerative Changes

• Joint areas– Knees: medial aspect

• Lumbar spines– Lower lumbar spines

L4-5

B S McGlone and K K Balan 2001 http://emj.bmj.com/content/18/6/424.full

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Bone Fractures• Bone scintigraphy is a very sensitive

exam for the detection of acute fractures [5].

• About 80% of bone scans will show increased activity at a site of fracture by 24 hours, and 95% by 72 hours,

B S McGlone and K K Balan 2001 http://emj.bmj.com/content/18/6/424.full

•Whole body bone scan showing multiple occult bilateral rib fractures (arrowed). •The linear alignment is typical of fractures.

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Stress Fracture-Left tibia

• Bone scan is much more sensitive than plain film for diagnosing stress fractures [5].

• More than 80% of stress fractures will not be evident on initial radiographs, while the sensitivity of bone scan approaches 100% [3].

A 19-yo man, a long- distance runnerhad left leg pain for one months, showing a fusiform increased uptake at posteromedial aspect of left tibia.

SriprapapornSriprapaporn J. Thai J Ortho 2012J. Thai J Ortho 2012 J. SRIPRAPAPORN

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Bilateral shin splints

Bilateral shin splints (medial tibial stress syndrome) in a young marathon runner showing the typical pattern of linear uptake in the tibial cortex.

B S McGlone and K K Balan 2001 http://emj.bmj.com/content/18/6/424.full

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Avascular Necrosis

1. Diagram shows how the vascular supply to the femoral head is maintained by the retinacular blood vessels in the pertrochanteric fracture of the femur.

2. Diagram shows how a subcapital fracture of the femoral neck cuts off of the blood supply to the femoral head, resulting in osteonecrosis

MRI: T2W

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• Clinical History: Woman, aged 68. Rest and stress pain in the right hip since an accident.

• Findings:

– SPECT images show an small area of intense uptake in medulla of the right femoral head.

– On Hawkeye CT a small area showing lack of contrast is visible. Fused dataset confirms co-registration of these areas.

http://www.gehealthcare.com

Avascular Necrosis

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Vascular phase

Soft-tissue

delayed 3-hr

Acute Acute OsteomyelitisOsteomyelitis

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Osteosarcoma

• Phase I : Vascular phase• Phase II : Soft tissue phase• Phase III : Bone phase

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Bone Metastases• Bone scan at

presentation and 3 months later

• Rib metastasis: expanding fusiformlesions

http://www.medscape.com/viewarticle/563750

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SuperScan

• Diffuse metastatic disease• Primary: prostate*, breast,

lung• Findings: Diffuse increased

uptake of skeleton with no/low renal activity

• Pitfall: May be missed as normal study.

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Flare phenomenon• The bone scan appears worsening, or even shows new

lesions, during the first several months following chemotherapy, while the patient's clinical condition improves

• This also occurs in patients following orchiectomy (17)and radiation therapy (18).

• A repeat bone scan will show marked improvement after several months.

• The flare phenomenon occurs in up to 20% of patients;depending on tumor type, therapeutic regimen and the interval between therapy and the bone scan.

• This phenomenon may persist upto 6 months.

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Conclusion

• Bone scan is a whole-body evaluation of bone activity.

• It’s is more sensitive than plain radiographs but it’s much less specific.

• The most common clinical application is to search for metastatic bone disease.

• Better interpretation needs knowledge of NM, clinical info, and also radiographic correlation.