Cardiology Radiopharmacuticals/procedure

What are the two types of Radiopharmaceuticals we can use for a cardiology procedure?

Thallium-201 chloride

Tc-99m labeled agents`

What is the extraction Fraction?

amount of radioisotope taken up in myocardium the first pass thru the heart

Why is the extraction fraction important?

important that majority of tracer is going to the myocardium(where it needs to go)

T/F: Tl-201 has a lower extraction fraction than Tc-sestamibi

False

T/F: Tl-201 has a higher extraction fraction than Tc-sestamibi or Tc-tetrofosmin

true

List the following tracers in order of extraction fraction (greatest to least):

Sestamibi

Tetrofosmin

O-15 H₂O

Tl-201

O-15 H₂O

Tl-201

Sestamibi

Tetrofosmin

What is the half-life of Thallium-201?

73.1hrs

How is Thallium-201 produced?

in a cyclotron

What are the keV’s of Thallium-201?

gamma: 135, 167 keV

x-ray 68-80 keV range

T/F: Thallium-201 emits both gamma and X-rays

true

How is Thallium-201 cleared from the body? What is the critical organ?

Renal

crit organ: kidneys

What is the method of localization of Thallium-201?

Active transport

sodium potassium pumps

What type of analog is Thallium-201?

potassium analog

What is the extraction fraction of Thallium-201?

85%

T/F: Thallium-201 remains fixed in the myocardium

false

How does does Thallium-201 localize in the myocardium?

sodium-potassium pumps move potassium ions in and out of plasma membrane of cell

Thallium is constantly pumped in and out

What are teh advantages of Thallium-201 imaging?

bc Tl constantly being pumped in and out, Tl can redistribute into ischemic areas on delay images

increased lung activity after exercise = marker for CAD, can calculate lung vs heart ratios

absence of significant hepatobiliary activity

What are the disadvantages of Thallium-201 imaging?

long half-life limits dose administered

low dose = poor count rate

low energy = poorly suited for imaging

gated SPECT problematic bc of redistribution

What is the stress imaging time when using Thallium-201?

5-10 min post injection

What is the imaging time for rest images using Thallium-201?

3-4 hrs post injection

T/F: you can get false negative scans if you wait too long after injection of Thallium-201

True - Tl redistributes and could fill ischemic areas

What percent of ischemic segments do not fill after 3-4hrs using Thallium-201?

15-35%

What is the purpose of reinjection when usign Thallium-201?

shown to demonstrate reversible ischemia more readily, increasing sensitivity of exam

When would you reinject Thallium-201?

prior to rest imaging

What is the dose of reinjection using Thallium-201?

1-1.5mCi prior to rest imagign

What is the dose for a Thallium-201 stress only image?

2-4 mCi

What are the dosages for a stress/reinjection study using Thallium-201?

2.5-3mCi stress

1-1.5 mCi rest

What is more common when using Thallium-201, a stress injection only, or stress/reinjection study?

1 stress injection of 3-4mCi

T/F: when using Thallium-201, the stress test is always performed first

true

Why should the stress test be performed first when using Thallium-201?

because of redistribution

T/F: Thallium-201 can be used for both treadmill or pharmacologic stress testing

true

What are the patient instructions between stress and rest images when using Thallium-201?

pts should fast or have light meal only (clear liquids)

pts should be advised to sit and rest (avoid physical activity)

Why should patients fast or have a light meal of clear liquids only when using Thallium-201?

eating between may have negative effect on myocardial redistribution of Tl - glucose ingestion results in increased clearance of Tl from myocardium

T/F: patients should be advised to rest between a stress and rest imaging when using Thallium-201

true

T/F: acquisition and positioning should be exactly the same for stress and redistribution(rest) images

true

What are the positions we can image patients for stress and redistribution (rest) images?

supine or prone

arms up or down

bra on or off

protocol varies

What are the different methods of acquisiton we can use for stress and redistribution (rest) images?

planar

gated planar

SPECT

gated SPECT

What are the two Tc-99m labled agents we can use for cardiac imaging?

Tc-99m Sestamibi (Cardiolite)

Tc-99m Tetrofosmin (Myoview)

What is the chemical name of Myoview?

Tc-99m Tetrofosmin

What is the brand name of Tc-99m Tetrofosmin?

Myoview

What is the chemical name of Cardiolite?

Tc-99m Sestamibi

What is the brand name of Tc-99m Sestamibi?

Cardiolite

What are the advantages of Tc agents over Tl?

higher injected dose = better sensitivity

more optimal energy

better target to background ratio

more rapid acquisition

more favorable dosimetry

fixed distribution provides flexability and permits SPECT gated studies

T/F: Tc agents have a fixed distrubition within the myocardium

true

T/F: Tc agents have more optimal energy than Tl

true

T/F: Tl has better target to background ratio than Tc agents

false

T/F: Tc agents allow for more rapid acquisition than Tl

true

What are the disadvantages of using Tc agents over Tl?

slightly lower blood clearence than Tl (slightly longer wait)

2 doses are needed

activity in liver, biliary and bowel can cause artifcats

myocardial extraction is 60% (sestamibi) and 50% (tetrofosmin) compared to Tl 85%

T/F: Tc agents have greater chance of having artifacts from the liver, gallbladder and bowel than Tl

true

What is the myocardial extraction of Tc-99m Sestamibi

60%

What is the myocardial extraction of Tc-99m Tetrofosmin?

50%

What is the myocardial extraction of Tl-201?

85%

How is Tc-agents made?

using a kit

What is the half life of Tc agents?

6.02 hrs

What is the energy of Tc agents?

140keV

What is the mechanism of localization of Tc agents?

passive diffusion

radiotracer diffuses across cfell membranes and then binds to a cell component

What is the mechanism of localization of Sestamibi?

binds to mitochondrial membrane inside myocardial cell

What is the mechanism of localization of Tetrofosmin?

localizes in mitochondria of myocardial cell

How are Tc agents cleared from the body?

hepatobilliary

What is the critical organ of Sestamibi?

large intestineWQ

What is the critical organ of Tetrofosmin?

gallbladder

What are the advantages of Tetrofosmin?

imaging can begin earlier bc:

rapid uptake

faster background clearance from liver and lung

What types of protocols can we perform using tc agents?

1 day stress/rest or rest/stress

2 day stress/rest or rest/stress

dual-isotope

What are the typical doses for Tc-99m Sestamibi?

dose range 10-30mCi

varies with protocol

What are the typical doses for Tc-99m Tetrofosmin?

5-24mCi

varies with protocol

T/F: when performing 1 day protocol, a smaller dose is used for the first imaging study and a larger dose on the second imaging study

true

T/F: when performing a 2 day protocol, a larger dose is used for both studies

true

How long after injection do stress images using Sestamibi and Tetrofosmin occur?

15-60min post injection

How long after injection do rest images using Sestamibi and Tetrofosmin occur?

30-90 min post injection

How is imaging time selected using Tc agents?

to minimize interfering liver, GB and bowel activity

How can we reduce GB activity using Tc agents? What will happen if we do? How can we offset that?

give glass of milk or fatty meal to clear excessive GB activity, but will result in greater bowel activity

can have pt walk around to try and clear bowel

What is the 1 day rest/stress protocol using Sestamibi?

1st dose rest :8-12mCi

2nd dose stres: 25-30mCi

What is the 1 day stress/rest protocol using Sestamibi?

1st dose stress: 10-15mCi

2nd dose rest: 25-30mCi

T/F: The stress portion must be performed before rest imaging using Tc agents

false

What are the dosages for a 2-day protocol using sestamibi?

20-30mCi both doses

What is the 1 day rest/stress protocol using Tetrofosmin?

1st dose rest: 5-8mCi

2nd dose stress: 15-24mCi

What is the 1 day stress/rest protocol using Tetrofosmin?

1st dose stress: 5-8mCi

2nd dose rest: 15-24 mCi

What is the dosage for a 2day protocol using Tetrofosmin?

15-24mCi

T/F: the order of the stress and rest imaging matters when performing a dual isotope protocol using Tc agents

true

What are the isotopes and dosages used during a dual isotope imaging procedure?

2.5mCi Tl-201 at rest

22-25mCi of Tc based agent at stress

When does imaging occur for both isotopes when performing a dual isotope procedure?

10-15 min post injection rest images using Tl

30-60min post injection (depending on isotope) stress imaging

What is the advantage of dual isotope imaging?

combines unique characteristic that Tl brings to access myocardial viability

What is important to remember when processing dual isotope images?

need 2 different filters bc of the 2 isoptopes

What is sensitivity of MPI for detection of CAD?

85%

What is the specificity of MPI for detection of CAD?

80-90%

What is the difference between sensitivity and specificity?

Sensitivity = how well an exam can detect the abnormal condition

specificity = level of detail provided