Instrumentation Oral Test Out

How and why do we do COR?

-180 and 90 degree acquisition. Looking at the effect of gravity on the detectors to see if anything is off tilt.

-Point source of tc. Make sure the point source is at the center of the circle of rotation. Point source should be in the middle of pictures the whole time.

-Incorrect COR would look like a doughnut90 degree COR looks like a doughnut. 180 degree tuning fork, facing outward

How would you do an intrinsic uniformity?

-take the collimator off. cameras facing each other. Point source

-5-15 million counts. 1-3 minutes.

-5 ufov. 800 uci about a 1 mci of tc99m

Imaging with an isotope other than tc99m. What could you do to ensure uniformity?

Uniformity correction map: done every 6 months to a year. A manual thing done by techs.

When using multiple energies, how would you check where the peak is at the isotope....

multiple window energy registration

How do we evaluate spatial resolution for dual head spect?

-jaszak phantom use the rods. Rods evaluate spatial resolution. Rods are the dots that get smaller and smaller with a birds eye views

-Cold spheres are looking at contrast. Evaluate contrast between cold spheres and tc99m water

-uniformity of the spect is just the water in the phantom.

What is the partial volume effect?

makes a lesion grow tighter or spread out. Spreads out and it makes it look larger and more faded by its averaging out the pixels

Thyroid probe QC

do the constancy with cesium, linearity with europium, high voltage check and efficiency test . Count the source and get a cpm we keep track of.

SPECT artifacts: Ring

caused by rotational issues. SPECT images because using a filter with a value of 1 below than frequency and 0 above it

SPECT artifacts: Ray

comes from back projection

SPECT artifacts: Truncation

attenuation correction errors

Dose calibrator linearity (quarterly)

-max dose in the department and go to the smallest dose (300 uci)

-One where you get source and you measure so often for days until you get to the minimum

-or you get the cali check sleeve method and add sleeves of lead that mimic decay to make the time shorter.

-30 uci is the minimum you need to go down to.

Gamma Camera QC Basics

Daily: extrinsic uniformity floor

Weekly: bars, and COR

Jaszack phantom use

Evaluation of SPECT uniformity

Injected with Tc99m

-We see a gray circle and know the dose of what we inject(10mCi)

-We are evaluating the WATER

Gamma camera geometry

measured in different volumes of liquid

Collimators:

Collimators: Pinhole

thyroid

Collimators: High energy

I-131

Collimators: Medium energy

indium

Collimators: Low energy

Tc99m

How to evaluate spatial resolution?

Weekly bars phantom

What a SPECT uniformity would look like if it's wrong?

A circle defect with empty space

What sheet source is daily uniformity done with?

Co-57

How do you close up the department?

Set up cameras for qc next morning

Weekly wipe, surveys of areas used

Survey yourself.

How often do you do geometry on dose calibration?

At installation and repair

Gas filled detectors

GM counter and dose calibrator

Solid state detectors

gamma camera and scintillator

Multiple window spatial resolution

-This test is for when you are using different isotopes so there are going to be different photopeaks. You are making sure that the events in the different photopeaks are being assigned to the same location

-Done quarterly

-Intrinsically image a bar photon using each photopeak separately

How do you do an intrinsic flood?

-Uses a point source for uniformity

-No collimator . 5-15 million counts. 1-3 minutes.

-Tests the detector only. Different volumes of liquid qeekly

-5 ufov. 800 uci about a 1mci of tc .

Describe different types of collimators and what they are used with and for

Low energy :

-140 kev tc99m

-I 123 159 kev

-max 150 kev

Medium energy

-I 123

-Max of 400 kev

High energy :

-I 131 364 kev

F-18 FDG: 511 kev

-Over 250 kev

Pinhole

-Thyroid or small organs

Parallel collimator

Where should the point source be for an intrinsic flood?

400-800 uci tc99m point source

5 UFOV diameter distance from camera

How do you look at resolution for SPECT?

A sinogram is assessed for patient motion

-Jaszczak phantom?

-Bar phantom?

How do you look at uniformity for SPECT?

-Jaszczak phantom: overall evaluation of image quality, lesion contrast, spatial resolution, uniformity

-Hamming filter

How do you look at sensitivity for a gamma camera?

Peaking and daily flood

Thyroid qc probe: Crystalline detector

Measures thyroid uptake.

PMT on the crystal base.

Important that the distance from the object being measured is fixed. Eliminate all sources of background radiation possible.

Thyroid qc probe: Constancy

Daily, uses cs137 to verify the gain settings or high voltage have not drifted

Thyroid qc probe: Calibration(peaking)

Daily, uses cs137 to verify peak is set for certain isotope

Thyroid qc probe: Chi square test

collecting 10 measurements from the cs137 standard and verify that the results fall within the 0.1 to 0.9 probability range

Thyroid qc probe: Energy resolution

Quarterly, uses cs 137 source or other monoenergetic source

Thyroid qc probe: Detector efficiency

Annually, correlates the measured count rate to the absolute activity using a radioactivity source of a known strength

What is a COR and how do you do one?

-Obtained using a point source and is trying to determine if the line of space of which a camera rotates is mapped to the center of rotation of the 3D image matrix

-Done weekly

-The space between the source and collimator doesn't matter

How do you do bars?(weekly)

-Bar phantom tests for spatial resolution and linearity, the smaller the bars look the better the resolution

-There's a four quadrant and parallel line equal spacing bar phantom type

Partial volume effect

-Intensity values in images differ from what it should be

-Contours of the voxel do not match the actual tracer outline so pixels on edges of source include both source and background tissue. Part of signal emanating from source is seen outside the actual object and is described as spilling out

What allows you to image multiple isotopes?

Pulse height analyzer: energy windows are selected to only allow certain photon energies that fall within a preset range to contribute to the output pulse

Circular vs elliptical vs body contour orbits in SPECT

Pro and cons of SPECT imaging

-Pros: 3D imaging to see structures better. Sensitivity

-Cons: increased noise, decreased resolution, patient motion

-Raw projection images 2D puts them together to make 3D reconstructed

What is linearity and how do we perform it?

-Dose calibrator control procedure performed to assess the devices ability to measure accurately a range of low to high activities

-Done quarterly

-Starting point for the linearity test is the highest activity used in the department

-Bar phantom camera?

Know weekly what we do : wipe tests, why we do them, how we record them, and in what unit they are measured in

Cpm

We do wipe tests to check for removable contamination

We record them in the computer/a log

Jaszack phantom : what is it used for?

Use phantom to know what resolution, image contrast, slice thickness, etc the camera is capable of. You know the true size of an object (its contrast) that you are interested in measuring. Standardized test procedure and compare month to month

What part of the phantom is used for what?

Phantom is used as a "stand in" for human tissue and checks the camera

-Spheres: lesion detectability . measure image contrast

-Lines

-Water: line spread measurements in water. Mimics photon properties of human tissue

-Rods: variation in spatial resolution within the field of view . mimic cold lesions in a hot background. Investigate image resolution in spect

Star effect

after ablation, see star shaped intense uptake of I131. caused by penetration of collimators septa by the gamma rays from high uptake. Large amounts of remnant thyroid tissue after surgery.

Daily qc dose calibrator constancy

Dose calibrator constancy : 100-200 uci cs137 (similar kev to mo99), 2-5 mci co57 (similar kev tc99m)

Daily qc: Well counter constancy, background, calibration peaking.

-Background make sure no contamination or radioactive source inn

-Constancy using cs137 long lived isotope (count rate and peak should be the same day to day , assuming the same energy window is used)

-Calibration peaking

Daily qc: flood and GM counter

Extrinsic daily flood

Check the geiger mueller counters : daily battery check, constancy

Why are daily constancy and calibration important for a thyroid probe?

constancy : cs137 to verify the gain settings or high voltage have not drifted

calibration peaking: cs137 to verify peak is set for certain isotope

Thyroid probe qc daily calibration

shows photopeak of cs137, window of 15-20 percent, other peaks are just Compton scatter. FWHM characterizes the quality of the spectrum's peak and should be less than 10%. Cs137 should peak between 400 and 500, represents the photo peak resolution , and checking the energy 661 .