Gamma Camera Instrument

Subgroup IV: Instrument Operations and Quality Control

What QC tests are run on a gamma camera?

calibration, uniformity, spatial resolution and linearity

gamma camera calibration frequency

daily, before use, ideally for each radionuclide to be used that day

gamma camera calibration sources

Co-57 for Tc99m, each radionuclide to be used that day

What will happen if the gamma camera is calibrated improperly?

photopeak set asymmetrically, will see hot or cold areas of flooding/image corresponding to PMTs

gamma camera calibration provides evaluation of

photopeak, scatter, characteristic x-rays

Compton edge calculation formula

Compton edge electron = (E₀²) / (E₀ + 0.2555)

What is the cause of the problem?

asymmetric photopeak (incorrect calibration)

gamma camera intrinsic uniformity

• point source, 300-500 uCi Tc-99m

• position source 5 FOVs away from the camera

gamma camera extrinsic uniformity

• 5-10 mCi sheet source, usually Co-57

• less than 1% non-uniformity

• liquid flood source with daily added Tc99m not recommended

• source goes on collimator

How many counts should be acquired for a gamma camera uniformity test?

1-3 million for visual analysis
15-30 million for quantitative analysis

gamma camera uniformity frequency

daily, each day of use
(non-routine floods weekly [intrinsic/extrinsic])

causes of gamma camera poor uniformity results

• uniformity map needs to be updated

• photomultiplier tube malfunctions

• crystal hydration/cracking

• collimator damage

• corruption of a correction table (energy or linearity)

• X- and Y-gain problems cause changes in size and shape of flood image

gamma camera uniformity troubleshooting

• improper pulse-height analyzer setting

  • too high, PMT’s appear cold

  • too low, PMT’s appear hot

• window size and effects on count rate and sensitivity

Given this field flood, what is the cause of the depicted non-uniformity?

measles due to hydration

Given this field flood, what is the cause of the depicted non-uniformity?

X-gain problem and adge packing

Given this field flood, what is the cause of the depicted non-uniformity?

asymmetric energy window

Given this field flood, what is the cause of the depicted non-uniformity?

peaking problem

Given this field flood, what is the cause of the depicted non-uniformity?

use of a Tc99m liquid phantom

Given this field flood, what is the cause of the depicted non-uniformity?

multiple window misregistration

Given this field flood, what is the cause of the depicted non-uniformity?

cracked crystal

Given this field flood, what is the cause of the depicted non-uniformity?

contamination (hot abnormality)

Given this field flood, what is the cause of the depicted non-uniformity?

PMT or pre-amplifier problem (cold abnomality)

gamma camera linearity definition

are the lines straight

gamma camera spatial resolution definition

tests the minimum resolving power of the camera (smallest bars seen, largest bars not seen)

methods for testing gamma camera spatial resolution and linearity

• bar phantoms and slit-masks

• line-spread function

• intrinsic vs extrinsic

frequency of gamma camera spatial resolution and linearity tests

weekly

causes of poor results on gamma camera spatial resolution and linearity tests

• improper pulse-height analyzer settings

• window width

• crystal, PMTs, collimator

• Moiré patterns

• star artifact

What is a Moiré pattern indicative of?

interference of collimator holes with bars

What is a star artifact indicative of?

seen when the gamma ray energy is high enough for significant septal penetration

What is this bar phantom?

Hine-Duley

What is this bar phantom?

Parallel Line Equal Spacing (PLES)

What is this bar phantom?

Four Quadrant

What is this bar phantom?

Orthogonal Hole

What is this bar phantom?

University of Buffalo (UB) — needs only one image to evaluate resolution in all 4 quadrants, in both the X and Y direction

What is the cause of the depicted abnormality?

linearity correction is turned off

What artifacts are seen in this image?

barrel and pincushion artifacts

What is the depicted abnormality?

Moiré pattern

What is the depicted abnormality?

star effect

What is this an image of?

SMPTE test pattern

What does a SMPTE test pattern test?

computer contrast and background controls, gray scale, and matrix sizes