Ch 11 - Instrumentation

Problems in Radiation Detection & Measurement

In vitro measurements on blood samples and urine specimens, and in vivo measurements of radioactivity in patients.

What are the two types of measurements in nuclear medicine instruments?

What is the desired maximum characteristic of a radiation measurement instrument?

Maximum detection efficiency.

It starts producing inaccurate results due to data losses and other data distortions.

What happens when counting rates exceed the threshold in nuclear medicine instruments?

detection efficiency

The efficiency with which a radiation measuring instrument converts emissions from the radiation source into useful signals from the detector.

geometric efficiency

The efficiency with which the detector intercepts radiation emitted from the source, determined by detector size and source-to-detector distance.

What does intrinsic efficiency measure?

The fraction of radiation striking the detector that interacts with it.

5 cm

What is the ideal thickness of the detector for optimal intrinsic efficiency?

A phenomenon when radiation particles interact closer to the edge of the detector, affecting intrinsic efficiency

What is the edge effect in radiation detection?

Geometric efficiency, intrinsic efficiency, fraction of output produced from the counting system, or absorption and scatter.

List the factors that can affect detection efficiency.

Because many counts are lost due to missing the isotropic 360 emissions from the isotope.

Why are helicopter scans avoided in radiation detection?

in vitro

what type of measurements are designed for blood samples, urine specimens and do forth?

blood samples, urine specimens, and so forth

what are in vitro measurements designed for?

in vivo

what type of measurements are designed to measure the radioactivity in patients

radioactivity in patients

in vivo measurements are designed to measure?

nuclear medicine instruments have special design characteristics to _____ them for their specific tasks

optimize

detection efficiency

an important consideration for any radiation measurement instrument is its __________.

maximum detection efficiency

_____ _____ _____ is desirable because one thus obtains maximum information with a minimum amount of radioactivity

counting rate

the instrument _____ ___ limitations are extremely important in nuclear medicine

finite

there are ____ counting rate limits for all counting and imaging instruments used in nuclear medicine

it starts producing inaccurate results due to data losses and other data distortions

what happens when counting rate are above the counting rate limit threshold

data losses and other data distortions

why are inaccurate results created when counting rates are above a threshold

detection efficiency

refers to the efficiency with which a radiation measuring instrument converts emissions from the radiation source into useful signals from the detector

the efficiency with which a radiation measuring instrument converts emissions from the radiation source into useful signals from the detector

detection efficiency refers to

large

it is desired to have as _____ of a detection efficiency as possible

to ensure you have the maximum counting rate from a minimum amount of activity

why do you want to have as large of a detection efficiency as possible?

geometric efficiency

the efficiency with which the detector intercepts radiation emitted from the source

detector size and source to detector distance

what determines geometric efficiency

the efficiency with which the detector intercepts radiation emitted from the source

geometric efficiency

intrinsic efficiency

the efficiency of the detector as it absorbed incident radiation events

the efficiency of the detector as it absorbed incident radiation events

intrinsic efficiency

intrinsic efficiency

primary function of detector thickness and composition

fraction of output produced from the counting system

important energy selective component that includes counts only from the desired range

absorption and scatter

in vivo studies encounter this error from radiation scattering or being absorbed in the patient

absorption and scatter

in vivo studies encounter this error from radiation scattering or being absorbed in the patient

1. geometric efficiency

2. intrinsic efficiency

3. fraction of output produced from the counting system

4. absorption and scatter

factors for detection efficiency

isotopically

radiation from a radioactive source is emitted _____

equal intensity in all directions

isotopically means:

missing the 360 emissions from the isotope

a majority of counts are lost due to:

lost

majority of the counts from the isotope are ___

when the detector is up really high

helicopter scans

because majority of the counts will be lost

why do we avoid helicopter scans

the intrinsic efficiency of the detector

what is it called when the fraction of radiation striking the detector that interacts with it?

the fraction of radiation striking the detector that interacts with it

the intrinsic efficiency of the detector

Ie = number of radiations interacting with the detector / number of radiations striking the detector

the formula for intrinsic efficiency

intrinsic efficiency

this value depends heavily on the detector material and thickness

detector material and thickness

what does the intrinsic efficiency depend on

5 cm

what thickness is ideal as it produces the highest % yield

5 cm

what size crystal has maximum efficiency

0.31 cm

what produces a smaller % yield, 2.5 cm or 0.31 cm

three

how many possible trajectories for radiations striking a detector from a point source

different

each trajectory will have a _____ intrinsic efficiency

edge effect

when radiation particles interact closer to the edge of the detector, a phenomenon called ____ can occur

when radiation particles interact closer to the edge of the detector

when does edge effect happen