NMT Boards – Instrumentation & QC

Gas-filled detector regions in order of increasing voltage

Recombination, ionization, proportional, limited proportional, GM, continuous discharge

Mnemonic for the gas ionization curve regions

Really Intelligent People Like Good Coffee

Two useful flat plateaus of the gas ionization curve

Ionization chamber and Geiger-Mueller

Gas-detector region in which the dose calibrator operates

Ionization chamber region

Gas-detector region with full Townsend avalanche and identical pulse sizes

Geiger-Mueller region

Gas-detector region that can distinguish alpha from beta particles

Proportional region

Why a GM meter cannot measure photon energy

Avalanche makes every pulse identical

Instrument of choice to FIND low-level contamination

GM survey meter

Instrument of choice to MEASURE accurate high exposure rates

Ionization chamber (cutie pie)

GM meter behavior at very high dose rates

Saturates and reads falsely low

Survey instrument used for therapy patient release readings

Cutie pie (ionization chamber)

Distances for patient release survey readings

Contact, 30 cm and 1 meter

NRC-required survey meter detection range

0.1 mR/hr to 100 mR/hr

GM probe that must be pointed directly at the source

End-window probe

GM probe used to survey a larger area

Pancake probe

Survey meter daily check-source tolerance per Bolus

Within 20% of calibrated reading

Survey meter annual calibration tolerance (10 CFR 35.61)

20%

Regulation governing survey meter calibration

10 CFR 35.61

When survey meters must be calibrated

Before first use, annually, after repair

Retention period for survey meter calibration records

3 years

Three daily survey meter checks before use

Battery, check source, calibration sticker date

Dose calibrator detector type

Pressurized well ionization chamber

Dose calibrator activity range

0.01 µCi to curies

Dose calibrator constancy frequency

Daily before use

Dose calibrator linearity frequency

Quarterly

Dose calibrator accuracy frequency

Annually

Dose calibrator geometry frequency

At installation and when changing syringe/vial size

Acceptable limit for all dose calibrator QC tests

±10%

Mnemonic for dose calibrator test frequencies

Can Linda Assay Good (C daily, L quarterly, A annually, G install)

Action when dose calibrator accuracy or constancy fails

Repair or replace

Action when dose calibrator linearity or geometry fails

Apply a correction factor

Dose calibrator test that measures precision (reproducibility)

Constancy

Dose calibrator test of accuracy across a wide range of activities

Linearity

Dose calibrator percent error formula

(Expected − Actual) ÷ Expected × 100

Correction factor formula

Expected ÷ Actual

True activity using a correction factor

Reading × CF

Minimum number of sources for dose calibrator accuracy

Two

Minimum activity of dose calibrator accuracy sources

50 µCi (preferably >200 µCi)

Energy range one accuracy source must fall within

100–500 keV

Half-life and energy of Cs-137

30 years, 662 keV

Half-life and energy of Ba-133

10.74 years, 356 keV

Half-life and energy of Co-57

271 days, 122 keV

Settings on which constancy is measured

Every commonly used radionuclide setting

Constancy expected 78.5 µCi, reads 70.1 µCi. Result?

10.7% error, fails; repair

Last week's constancy average 142.2 µCi. Acceptable range?

128.0 to 156.4 µCi

Lowest activity for linearity decay testing (Bolus)

30 µCi or less

Lead-sleeve method for same-day linearity

Shield method (Cali-check or Lineator)

Short-lived isotope usable for same-day linearity decay test

F-18 (110 min)

5 mL syringe should read 2.95 mCi but reads 2.45. Correction factor?

1.2

Dose in that syringe reads 12.6 mCi with CF 1.2. True activity?

15.1 mCi

Retention period for dose calibrator QC records

3 years

Geometry of a well counter

Near-4π

Most sensitive sample counter in nuclear medicine

Well counter

Activity above which a well counter shows dead-time losses

About 2 µCi

Lead shielding around a well counter detector

About 5 cm

Minimum counts for well counter or probe samples

10,000 counts

Percent error for 10,000 counts

1%

Percent uncertainty formula

100 ÷ √N

Unusually HIGH well-counter constancy reading suggests

Contamination or a nearby source

Counting efficiency formula

DPM = CPM ÷ efficiency

Well counter efficiency 85%, wipe 120 cpm net. DPM?

141 dpm

Collimator type on a thyroid uptake probe

Flat-field collimator

%RAIU formula

(Neck − Thigh) ÷ (Standard − Background) × 100

Purpose of the thigh count in RAIU

Corrects for non-thyroid body background

Neck 12,000, thigh 2,000, standard 42,000, bkg 2,000 cpm. RAIU?

25%

Is the uptake probe standard capsule diluted?

No

Cs-137 10% window LLD and ULD

629 and 695 keV

Energy resolution formula

FWHM ÷ photopeak energy × 100

Smaller energy resolution percentage means

Better resolution (narrower peak)

Typical Cs-137 energy resolution for a probe

8–12%

Cs-137 FWHM 535 to 605 keV, peak 570. Energy resolution?

12.3%

Scintillation spectrometer energy resolution frequency

Annually

Well counter/probe voltage calibration (peaking) frequency

Daily

Well counter/probe constancy tolerance

±10%

Correct operating voltage during peaking

Setting with the highest count rate

Chi-square formula

Σ(N − N̄)² ÷ N̄

What chi-square tests

Whether count spread matches random decay

Bolus chi-square protocol

10 counts, 9 degrees of freedom

Acceptable chi-square P value range

0.1 to 0.9

Chi-square 46,998 ÷ 10,016 = 4.69 with 9 df. Result?

Acceptable (P 0.5–0.9)

Counting statistics: % within ±1, 2, 3 SD

68%, 95%, 99.7%

Room pressure required for Xe-133 and aerosol use

Negative pressure

Photon energy of Xe-133

81 keV

Half-life of Xe-133

5.24 days

Regulation known as the xenon gas rule

10 CFR 35.205

Order of ventilation and perfusion in same-day Xe-133 V/Q

Ventilation before perfusion

Common aerosol ventilation agent

Tc-99m DTPA

Fraction of loaded aerosol activity reaching the lungs

About 1–3%

Ultrafine carbon pseudogas preferred in COPD

Technegas

Bruce protocol stage length

3 minutes

Bruce stage 1 speed and grade

1.7 mph, 10%

1 MET equals

3.5 mL O₂/kg/min

Instrument required for H-3 wipe tests

Liquid scintillation counter

Maximum beta energy of H-3

18.6 keV

Quench type where light is never produced

Chemical quenching

Most common LSC quench correction method

External standard ratio (Ba-133)

Half-life of Rb-82

75 seconds

Only acceptable Rb-82 generator eluent

Additive-free 0.9% saline

Volume of Rb-82 eluate discarded each day

First 50 mL

When Sr breakthrough must be measured

Before the first patient dose each day