Skeletal Test Out

how does barium affect our bone scans

causes cold spots

What type of scan would we do for osteomyelitis

3 phase

what is the latest we can do delays on a bone scan

24 hours to see if initial moderate uptake will increase over more time

what are the three most common cancers for metastases

breast, prostate and lung

MOA for MDP/HDP

chemisorption

what is chemisorption 

the chemical bonding of a adsorptive and surface

what two RPx are palliative care treatments for bone pain

Ra-223 (xofigo) and Sr-89 (metastron)

osteoblasts

build bone

osteoclasts

destroy bone

osteocyte

bone cell

what two hormones are involved in the formation of bone

thyrocalcitonin (calcitonin) and parathyroid hormone

calcitonin

produced by c-cells and decrease osteoclasts

PTH

regulates calcium and phosphate levels in plasma

how does osteoclastic activity affect our scans

it decreases accuracy and specificity

why is nuclear medicine good for imaging bones

highly sensitive, can see problems with only 4-5% decalcification (can see 6mo-2yr earlier than XR)

what does our RPx bind to

Ca2+ in bone

what is the main difference between MDP and HDP

HDP clears a little quicker

How much of the dose is in the bone by 2-3 hrs

50% 

how much is excreted through urine by 24 hrs

50%.

when is the best TNT ratio

3 hours

how does excess colloid in the RPx prep affect our scans

it increases the liver uptake

what can cause altered distribution of bone agents

• chronic treatment use of steroids (decrease uptake)

• breast tissue from breastfeeding

• sickle cell (increase spleen uptake)

• increased albumin levels (increase liver)

• physical objects

what are some uptake factors

• Bone remodeling

• growth

• capillary/membrane permeability

• flare response

what is the flare response

seen a few weeks to months after therapy treatment that signal osteoblastic/reparative activity around mets or other lesions

MDP dose

20-30 mCi

imaging time for WB bone

2-3 hr post inj (up to 24 hr)

pt prep and prereqs for bone scans

• informed consent

• no NM studies 2 days before or after

• no contrast studies

• pregnancy and BF

what question for we need to ask for Hx

• Hx of Fx, trauma, falls, cancer

• recent NM studies or previous bone scans

• “why are you here”

• implants, hardware, prosthesis, etc

• dental work

WB bone acquisition parameters

WB: 256×1024 matrix for 1.5 million counts

Spots acquisition parameters

5k-1mil counts for thorax/abdomen

250k-400k for skull/large joints

150k-250k extremities 

128×128 or 256×256 matrix

constant ID acquisition

• adjusts to the number of counts in each frame

• slower for areas with less uptake and vice versa

• causes variable or longer scan times (scheduling issues)

• causes reproducible scans but can mask super scans and lower resolution

constant table speed

• most used today

• table moves at a constant speed no matter the patient

• consistant scan times allow better comfort for patients and help with scheduling

• allows for imaging consistency and uptake accuracy 

• 2048×256 

constant imaging time

• same scan time for all patients (ex 20 mins for everyone)

• can cause issues for ranging heights 

  • 5’6 will be good quality but 6’5 will not 

• 1024×1024 matrix

• dose dependent

• good for scheduling

• same resolution between patients scans but not between different patients

step and shoot

• series of static put together

• better resolution 

• patient motion can lead to alignment issues

  • should follow up with SPECT

where are typical statics taken

• sides of heads

• obliques of ribs/arms

• any suspicious uptake areas

why would we follow up a WB with a SPECT

Dr wants a more detailed look at a suspicious area that the planar didnt give enough info on

SPECT acquisition

360º with 6º per stop for 60-120 stops, 10-40 sec per stop

64×64

what are typical uptake distributions on a normal bone scan

sacroiliac joints, acetabular. joints, glenoid fossa, ends of long bones, vertebral column, growth plates, kidneys/ureters/bladder, sternum, C-spine

why might a more obese patients have higher soft tissue uptake

due to compton scatter

what are some things we might see with RPx issues 

free tc→ thyroid, stomach, GI tract

colloid formation in RPx causing high liver and RES uptake

step one of a 3 phase scan

blood flow

• pt on camera with AOI over FOV

• inject on camera for 30-60 images at 1-3sec/frame

64×64

step 2 on 3 phase scan

blood pool

• 5 min static image

• 128×128

• about 300k counts

• send away for normal delay time

step 3 on 3 phase scan

normal delay images 2-3 hours post injection

osteomyelitis on a 3 phase

hot on all 3 phases→ delays even hotter

cellulitis on a 3 phase

hot blood flow and pool but normal delays

what are bone scans not sensitive for

osteocastic lesions

• multiple myeloma, eosinophilic granduloma, etc

what skeleton do most mets go to

axial skeleton

how does a PET scan play into metastatic disease

even if a patient got a initial WB bone scan, they need a PET for cancer staging

clinical indications; inflammatory diseases

• osteomyelitis

• cellulitis

• arthritis

clinical indication; trauma and Fx

• positive in 3-5 days

• 80% of Fx positive in 24 hrs; 95% in 72 hr; 98% in 1 week

why do we need to wait a few days if we were to image for trauma or Fx?

there needs to be growing bone but it stays positive for a very long time

clinical indications; bone viability

• frost bite

• avascular necrosis (cold spot)

• bone graft

• sickle cell anemia

clinical indications: other

• localization of Unk bone pain, biopsy site eval, alkaline phosphate levels, joint/prosthesis pain, follow up for therapies

bones scans; metastatic disease

• most sensitive for mets

• breast, prostate, lungs

what is the main mineral composition of bone?

hydroxyapatite

why cant calcium or phosphorus isotopes be used for routine bone scans

because no suitable gamma emitting isotopes exist and calcium isotopes are only high energy or beta emitters

what determines the uptake of MDP/HDP

osteoblastic activity and blood flow to the bone

how does crystal size affect RPx uptake

smaller hydroxyapatite crystals have greater surface area-to-volume ratios, allowing more RPx binding

why do growth plates show up on bone scans

they have high osteoblastic activity and a larger surface area to volume ratio

what type of bone lesions would appear “Cold” on a bone scan

lesions with reduced blood supply or osteoblastic activity (infarction, necrosis, lytic tumors)

what type of bone lesions would appear “hot” on a bone scan

lesions with increased osteoblastic activity and blood flow (fractures, infections, metastases, pagets)

how can the bladder dose be minimized

by good hydration and frequent voiding

what does the blood flow on a 3 phase evaluate

regional blood flow and perfusion to the area of interest

what does the blood pool phase evaluate

blood volume in soft tissues surrounding the suspected pathology

what does the delay on a 3 phase show 

tracer uptake in the bone-correlates to osteoblastic activity

what happens if images are taken too early (<2 hrs)

higher soft tissue background (lower diagnostic quality)

how can renal excretion of unbound tracer be improved

by patient hydration

recommended patient hydration protocol for bone scans

250 mL water before injection

is fasting required for a bone scan

no

what can be done for a patient who cannot drink fluids

administer IV hydration or allow longer delay before imaging

what effect does excessive bladder activity have

can obscure the sacrum, pubis, and pelvis on images

what are common sources of false “hot spots”

skin or clothing contamination, especially if urine gets on the patient

when are pinhole collimators useful

for magnified views of small bone or localized lesions

how much bone mineral must be lost before lesions become radiographically detectable

30-50% of bone mineral loss

what is the most common bone scan pattern for metastases

multiple focal areas of increased tracer uptake (hot spots), often asymmetric int he axial skeleton 

what non-malignant disorders can mimic multifocal metastatic uptake

fibrous dysplasia, pagets disease, osteomalacia pseudofractures and multiple insufficiency fractures

what determines the distribution of bone metastases

the distribution of active red marrow and the tumor type

what non-malignant conditions can cause a super scan

metabolic bone diseases (hyperparathyroidism, renal osteodystrophy, pagets)

which tumors often have bone metastases detectable on scintigraphy despite being asymptomatic

lymphomas and neuroblastomas

what three radiopharmaceuticals used for infection imaging

Ga-67, In-111 and Tc-HMPAO

how can avascular necrosis be determined on a bone scan

cold defect surrounded by a hot rim

why do we want to know about fractures within a year or so

because fractures can still show uptake 6-12 months if not longer

what can minic a stress fracture on bone scans

shin splints, osteoid osteoma or a focal infection

how can bone scintigraphy assess prosthetic joint complications

to distinguish loosening (increased delayed uptake only) from infection (increased uptake in all three phases)

what is avascular necrosis

bone death caused by interrupted blood supply, leading to ischemia and necrosis of bone tissue

what are common causes of AVN

trauma, coricosteroid use, alcohol abuse, radiation therapy, sickle cell disease, and idiopathic causes

what causes pagets disease

abnormal bone remodeling with increased osteoclastic reabsorption followed by excessive, disorganized bone formation

what is the characteristic pattern of pagets disease on a bone scan

intense, sharply defined uptake in one or more bones, often expanding the normal bone outline

what bones are most commonly affected in pagets disease

pelvis, skull, spine, femur and tibia

how does pagets disease appear on a skull bone scan

“cotton wool” appearance- patchy, irregular areas of intensity

how does pagets differ from metastases on a bone scan

pagets= uniform intense uptake in a singleexpanded bone

mets= multiple focal hot spots

what causes increased vascularity in pagets disease

hyperactive bone turnover increases blood flow and osteoblastic activity

how is pagets disease monitored on bone scans

by comparing intensity and extent of uptake before and after treatment

how does pagets appear on follow-up scans

decreased intensity of uptake in previously active regions

what bone changes occur in hyperparathyroidism

diffuse skeletal demineralization with areas of subperiosteal bone reabsorption and “brown tumors”

what is a brown tumor

a localized area of bone reabsorption filled with fibrous tissue- appears as a hot lesion on bone scan

what bone scan pattern suggests hyperparathyroidism

diffused skeletal uptake with accentuation of cortical margins and uptake in distal clavicals, skull and long bones

what does the “metabolic superscan” pattern indicate

uniformly increased skeletal activity with faint or absent renal visualization, due to high bone turnover

what conditions can produce a metabolic superscan

hyperparathyroidism, renal osteodystrophy, and sometimes pagets disease

what causes renal osteodystrophy

chronic renal failure→ secondary hyperparathyroidism→ abnormal bone turnover and minieralization