Oncology/Misc Test-out

what is the physical half life of Ga-67?

78 hrs

what is Ga-67 biological half life

25 days

What is Ga-67 MOA

active transport

what does Ga-67 bind to

lactoferin and transferin

where does Ga-67 bind to transferrin?

in the plasma

where does Ga-67 bind to lactoferrin?

in the tissues

where does unbound Ga-67 go?

cleared by kidneys

Why does high iron levels affect the distribution of Ga-67

less liver uptake, more kidney uptake and faster clearance

How much gallium is renally excreted in the first 24 hrs

10-30%

what becomes the main excretion pathways for Ga-67 after 24hr

GI tract

should kidneys normally be seen on 72 hr Ga-67 scans?

no

what does 72 hr kidneys uptake mean?

acute tubular necrosis, renal disease or liver disease

what happens if “carrier gallium” (hot+cold) is used instead of carrier free?

biodistribution shifts and skeleton becomes a major site of uptake

what is the main organ of Ga-67 uptake

liver

where is Ga-67 normally distributed in the first 24 hrs

renal cortices

what bone related uptake is seen in Ga-67 scans

bone marrow, skeleton and growth plates (children)

why do the nasopharynx, salivary and lacrimal glands show in Ga-67 uptake

they have high lactoferrin levels

when is bowel uptake most visible with Ga-67

on delayed images

what breast conditions cause Ga-67 uptake

menstrual cycle, pregnancy, breast feeding and birth control

does Ga-67 concentrate in breast milk

yes

what percentage of Ga-67 remains in the circulating blood pool

about 20%

can Ga-67 uptake be seen in the thymus

yes, mainly in children

Ga-67 citrate dose

4-6 mCi

when are the delayed images for Ga-67

48 and 72 hrs post inject

which photopeaks are used for ga-67 tumor imaging

93, 184, 296 keV

what type of collimator is used for Ga-67 tumor imagine

medium energy collimator

which tumors are typically Gallium avid?

lymphomas, hepatocellular carcinoma, bronchogenic carcinoma, testicular carcinoma, melanoma, mesothelioma, soft tissue sarcoma

why do tumors accumulate Ga-67

leaky abnormal capillaries and iron-binding proteins in the tumor

why should whole-body imaging be performed with Ga-67 tumor scans?

recurrent disease is often metastatic

how long should you wait to re-scan with Ga-67 after chemo?

at least 3 weeks

does ga-67 localize in scar tissue or necrosis

no it localizes. in viable tumor tissue only

what tracer can help differentiate tumor from inflammation

Thallium-201

why is the Ga-67 dose higher for tumors vs infection imaging

a higher dose might be needed to uptake the tumor cells where as even acute infections will show with smaller doses

when are Ga-67 infection images taken

24-48 hrs

what can help distinguish bowel activity from pathology on ga-67 scans?

serial imaging or oral sulfur colloid to outline bowel lumen

why might abdomen imaging with Ga-67 be difficult

high liver uptake obscures nearby structures

what can you do to improve abdominal imaging with Ga-67

sheilding the liver, excluding it from the FOV or doing a sulfer collid subtraction study

what tissue does Tl-201 preferentially accumulate in?

viable tumor cells

is thallium uptake affected by chemo, radiotherapy or steroids

no it. remains essentially unaffected

optimal imaging time after thallium-201 injection

20-60 minutes

for lymphomas, when are delayed Ti-201 images taken?

up to 3 hrs post-inject

typical thallium-201 dose for tumor imaging

3-4 mCi

what type of collimator is used for thallium imaging

low energy collimator

normal thallium-201 uptake sites

choroid plexus, lacrimal glands, salivary glands, thyroid, myocardium, liver, spleen, kidneys, testes, splanchic regions

what is the half life of thallium-201

3 days

critical organ for thallium-201

kidneys

thallium vs gallium in kaposi’s sarcoma

its thallium-positive and Gallium-negative

thallium vs gallium in infection

gallium-positive and thallium-negative

what happens if tumor imaging is delayed too long after thallium injection

tumors may be missed due to washout

how does thallium help in brain tumor evaluation

differentiates rercurrent tumor (positive) from post-radiation necrosis (negative)

how does thallium uptake relate to tumor grade?

uptake intensity parallels malignancy grade

why is thallium useful in thyroid carcinoma patients

low radiation dose, no need to stop thyroid hormone replacement, and some thyroid cancers don’t take up iodine

which tumors is thallium not very useful for

pulmonary mets, bone mets, distant mets

why is thallium useful in primary bone tumors

it does not reflect bone healing, so it can track response to chemotherapy

thallium vs MIBG in breast cancer imaging

Tc-MIBG provides better images and higher doses; thallium accumulates in malignant breast tumors but rarely benign ones

is thallium uptake specific for lung cancer

no it also accumulates in TB, pneumonia, silicosis and radiation pneumonitis

how can delayed thallium imaging help in lung disease

washout occurs in inflammatory lesions but persists in carcinoma

what is Indium-111 octreotide also known as

In-111 DTPA pentetreotide

what hormone is octreotide an analog of

somatostatin

normal actions of somatostatin

inhibits release of growth hormone, insulin, glucagon and gastrin

which tumors have somatostatin receptors

islat cell tumors, carcinoid tumors, small cell ling carcinoma, neuroblastomas, pheochromocytomas, paragangliomas, medullary thyroid carcinoma

non-apudomas that may also show somatostatin receptors

lymphomas, meningiomas, astrocytomas, breast cancers, sarcoidosis, TB

how does biodistribution of In-111 octreotide change over time

most leaves plasma within 1 hr; only about 1% in blood at 20hr

normal uptake sites for In-111 octreotide

pituitary, thyroid, liver, GB, spleen, kidneys, bladder

which normal organs are “hottest” with octreotide

spleen and kidneys

critical organs for In-111 octrotide

spleen

main excretion pathway of octreotide

kidneys (85%), minor biliary

patient prep before octrotide imaging

hydration, bowel prep for 24 hr images

which patients may not be suited for octreotide imaging

those with poor renal function

when should octreotide imaging be delayed in treated patients

if on octreotide acetate therapy, wait 24-72hr

examples of false-positive octreotide uptake

URI (nose/lung hilum), thyroid in graves disease, orbits, joints in rheumatics

In-111 octreotide dose

5-6 mCi

imaging times for octreotide

4 hr (ROI), 24 hr (eyes to thighs), possible delays up to 48 hr

what else is octreotide called

octreoscan

what are the two main RPx for infection imaging

Ga-67 citrate and In-111 WBC

most common indications for infection imaging

osteomyelitis, acute cholecystitis, post-op opportunistic infections, abscess ocalization, infected grafts, inflammatory bowel disease

why use NM for infection imaging

helpful when CT, US or MRI fail to localize a lesion

what chemicals are released during acute inflammation

histamine and other mediators

what effect do acute inflammation chemicals have?

increase blood flow, increase capillary permeability → proteins + fluid enter → edema

which immune cells invade early in inflammation

macrophages at about 30 min, neutophils peak at 24hr

which cells dominate in chronic inflammation

monocytes

production method of Ga-67

cyclotron-produced, carrier-free

excretion pathway after 24hr for ga-67

GI tract via bowel mucosa or biliary

excretion pathway of Ga-67 first 24hr

renal

critical organ for Ga-67

large bowel

why does Ga-67 accumulate in infections

binds to transferrin, lactoferrin, bacterial siderophores and macrophages

what collimators are required for ga-67 imaging

medium or high energy

normal biodistribution percentages of Ga-67 at 1 week

20% liver, 20% skeleton, 25% soft tissue, 10% bowel excretion and 25% blood pool

variant normal uptake for Ga-67

lacrimal/parotid/submandibular glands, thymus, hilar nodes, breasts

abnormal Ga-67 uptake commonly seen in

opportunistic infections, FUO, chronic infection, osteomyelitis

strength of Ga-67 for infections imaging

works in neutropenic and chronic patients (doesn’t rely on WBCs)

downsides of Ga-67

long imaging delays, poor gamma energies, colon activity can mask abcesses

What % of neutrophils are in bone marrow vs circulation

90% marrow, 10% circulation

normal biodistribution of In-111 WBC’s

30% spleen, 30% liver, 34% marrow, 6% rest of body

excretion of In-111 WBCs

none

critical organ for In-111 WBCs

spleen

gamma energies for In-111

171 and 245 keV

In-111 half life

67 hrs

typical imaging time for In-111 dose

0.5-1 mCi (500uCi-1mCi)

how much blood is needed to label In-111 WBCs

50-60 ml