Radiation Counting Systems

How radiation counting systems are used?

Are used for a variety of purposes in nuclear medicine

Vitro counting systems

are used to measure radioactivity in tissue, blood, and urine samples. (Dose calibrator, or a automated system capable of processing hundreds of samples in a batch.)

Vivo counting systems

are employed for measuring radioactivity in human subjects or experimentally in animals. (Specialized systems have been made to scan individual organs like a thyroid probe.)

Most nuclear medicine counting systems consist of these basic components:

a detector, high voltage power, preamplifier, amplifier, one or more single channel analyzers or a multichannel analyzer.

What does a NaI(Tl) well counter look like?

Is a single crystal of Nal(Tl) with a hole in one end of the crystal for the insertion of the sample.

What will help to limit the background count of a Nal(Tl) well counter?

5 cm or greater of lead.

Why the detection efficiency of NaI(Tl) well counters for most gamma-ray emitters is quite high?

Their near 100% geometric efficiency.

What the intrinsic efficiency of the well counter depends on?

gamma ray energy and on the thickness of Nal(Tl) surrounding the sample

what depends on when the fraction of gamma rays escaping through the hole at the end of the well counter?

The position of the source in the well.

What is the percentage lost when the source is near in the well?

7%

What happens when the source is near the top or even at a larger distance from the well counter?

Decreases the counting efficiency to 50% and even larger when further.

Are gas filled detectors inefficient for most gamma ray energies encountered in nuclear medicine?

True

Is gas filled detectors still find some applications speciallized applications?

True

Is a Dose calibrator a gas filled detector?

True

What does a gas filled detector of a Dose calibrator typically filled with?

Argon Gas

What does the gas filled dose calibrators don’t have?

No energy discrimination, it only detects the total amount of radiation present in the sample

How are gas filled detectors are also used in the gas flow counters

which are primarily used for the measurement of Beta emitting radioisotopes

What are the current applications for the gas-flow counters?

monitoring the effluent from gas chromatographs.

What are the gases in a gas-flow counters?

H3 or C14 in helium carrier gas as they pass through the detector showing the activity.

What is vivo counting systems?

These are used to measure radiation concentrations in patients and occasionally animals.

What are probe systems?

Systems designed to monitor radioactivity in single organs or in localized parts of the body

What are single probe used for?

thyroid uptake scans (I-123)

what does the multiple probe systems are used for?

renal function studies, lung clearance studies, brain studies to generate washout curves.

Is whole body counters a vivo measurement?

True

What are whole body counters designed for?

to measure the total amount of radioactivity in the body

What si the whole body counters can’t do?

no attempt at localizing the activity distribution in these counters

What are these whole body counters used for to study?

studying retention, turnover & clearance rates with nuclear studies like Co60, Co57, Na24, K42, Ca47, & Fe50