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Y2 Nuclear Medicine - MPY8009 > Gamma Camera QC > Flashcards

Gamma Camera QC Flashcards

1
Q

What is the difference between quality assurance and quality control and where is it defined?

A

Quality Assurance: Planned actions to ensure a system or process meets standards.
Quality Control: Specific operations to monitor, maintain, or improve quality, focusing on measurable performance characteristics.
Define in IR(ME)R2017.

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2
Q

What is a critical examination?

A

This is required if the installation include x-ray equiqment or houses a sealed radiation source.
This is the duty of the installer under IRR17.
Purpose is to check the presence and function of radiation safety features that protect operators

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3
Q

What is Acceptance Testing?

A
  • Ensures equipment meets performance standards agreed at procurement.
  • Trigger for final payment and required before patient use.
  • Tests assess performance against manufacturer metrics.
  • Standards: Typically use NEMA, with IEC standards also applicable.
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4
Q

What is the purpose of Commissioning?

A
  • Establish baseline performance as measured by local routine performance tests
  • Establish a QA/QC routine and protocols for the scanner
  • Set up and optimise clinical acquisition protocols
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5
Q

What is ‘Routine Testing’?

A
  • Primarily asks – is the equipment in a fit state for clinical use now
  • Is there evidence of deterioration that can be addressed proactively
  • Needs to be simple and time efficient to perform
  • Tests typically undertaken by the equipment user
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6
Q

There are 9 main tests

What are the example QC tests for a Gamma Camera?

A
  • Uniformity (Intrinsic/Extrinsic)
  • Spatial Resolution
  • Sensitivity
  • Energy resolution
  • Centre of rotation
  • Whole body acquisition function
  • Tomographic image quality
  • For SPECT/CT - CT tests and SPECT-CT registration
  • Absolute quantification
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7
Q

How can the uniformity be tested intrinsically or extrinsically?

A

Uniformity can be tested as Intrinsic uniformity (collimator off) using a point source at a distance or extrinsic uniformity (with collimator on) using a s flood source (Co-57).
They are assessed visually (qualitatively) or quantified.

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8
Q

What are the factors affecting uniformity?

A
  • PMTs (tuning, gain, PMT drop out)
  • Damage to crystal/crystal hydration
  • Linearity, energy, uniformity (sensitivity) maps – have these been applied correctly? Do they need updating?
  • Temperature fluctuations
  • SPECT acquisitions – centre of rotation errors and poor attenuation correction can also cause non-uniformities in the reconstructed image
  • Test set up/user error (!)
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9
Q

What is the Integral Uniformity?

Write the equation

A

Integral uniformity is the difference in contrast between hottest and coldest pixels anywhere in the image.

Integral Uniformity = (cmax - cmin)/(cmax + cmin) x 100%

cmax = counts in hottest pixel
cmin = counts in coldest pixel

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10
Q

What is the Coefficient of Variation?

Write out the equation

A

Coefficient of variation measures the overall variation in pixel counts across the field of view (standard deviation over the mean).

CoV = 100% x Standard Devation/ Mean

Standard Deviation = √(Σ(Cij-M)^2)/N

Mean = Σ(Cij)/N

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11
Q

What is the differential Uniformity?

Write the equation

A

Differential uniformity measures change in counts within a local group of 5 pixels.

D = (H-L)/(H+L) x 100%

H = Highest count in 5 adjacent pixels
L = Lowest count in 5 adjacent pixels

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12
Q

What is the spread of Differential Uniformity?

Write the equation

A

Spread of differential uniformity gives an indication of how rapidly the uniformity varies across the image.

Spread of Differential Uniformity =
√(Σ(Dijh)^2 + Σ(Dijk)^2/N)

Dijh = cij -ci+h,j/cij + ci+h,j
Dijk = cij =ci,j+k/cij + ci,j+k

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13
Q

What is the relationship between the Central Field of View (CFOV) and the Useful Field of View (UFOV)?

A

CFOV is the same shape as UFOV but with 75% of its linear dimensions.

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14
Q

What determines the Geometric Field of View (GFOV)?

A

GFOV is determined by the edge of the collimator aperture(s).

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15
Q

How do you measure the sensitivity of a gamma camera?

A
  1. Fit required collimator
  2. Draw up activity (10-20 MBq), note calibrator measurement & time
  3. Fill sensitivity phantom
  4. Measure residue and time
  5. Place source on collimator surface and image for 2 min, noting acquisition time
  6. Remove source and obtain background image for 2 min
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16
Q

What is the sensitivity calculation?

A

Sensitivity = (total counts in source image) - (total counts in background) / (decay corrected syringe activity) - (decay corrected residual activity)

17
Q

How is the spatial resolution tested?

Write the equation for system spatial resolution

A

Measurements can be made intrinsically or as a system test, qualitatively or quantitatively – IPEM recommend making quantitative assessments of both annually

(Rsystem)^2 = (Rgeo)^2 + (Rintrinsic)^2

18
Q

How is intrinsic spatial resolution measured?

A
  1. Remove collimator and protect crystal surface.
    2 . Mark positions of each PMT
  2. Position collimated point sources over centre of a few PMTs
  3. Set up acquisition using Tc99m energy peak (check peaking) and a matrix to give pixels ≤0.7mm
  4. Acquire ~2000 counts in max pixel
  5. Draw wide profiles across the sources in X and Y directions and determine FWHM and FWTM
  6. Repeat for ~ 12 tubes and again for sources midway between PMTs
19
Q

How is the system spatial resolution measured?

A
  1. Fill pair of capillary tubes with ~200MBq
  2. Position parallel to each other 100mm apart and camera axis through centre of the field of view.
  3. Acquire using Tc99m window, matrix to give pixel size ≤1mm for long enough to achieve ~400 counts in maximum pixel
  4. Measure FWHM and FWTM in terms of pixels
  5. Use number of pixels between lines to verify pixel size and convert to mm unit
  6. Repeat for x/y direction, at 0 cm and 10 cm from the collimator and for each detector/collimator available
20
Q

How is the spatial resolution assessed visually?

A

Visual assessment of transmission phantoms with bar / quadrant patterns.

21
Q

What is the added value of the spatial resolution test?

A

If both the uniformity and spatial resolution fail from visual inspection but a new uniformity map doesn’t resolve the issue then this can indicate an issue with one of the PMTs which requires a full service.

22
Q

What are the different wholebody testing methods?

A
  • Wholebody System Uniformity
  • Wholebody System Spatial Resolution
  • Wholebody Count Rate Variation
  • Wholebody Exposure Time Correction
23
Q

Why do the cameras stay stationary at the beginning and end of a wholebody acquisition?

A

In the stationary position the aquisition windows moves across the face of the camera, this is referred to as the “ramp”.

24
Q

How is wholebody uniformity tested?

A

Using a large flat uniform source placed on the bed and acquired using a wholebody aquisition.

25
Q

How is wholebody spatial resolution tested?

A

Fillable line scaned as a wholebody acquisition.

26
Q

How is the whole body exposure time correction tested and what does it check for?

A
  1. Use highest sensitivity parallel hole collimator
  2. Flood source attched to the head of the detector and run maximum length wholebody scan
  3. Rebin into 64x256 matrix, by resampling it controls the noise
  4. Image reviewed visually and summed profile used to calculate the mean, standard deviation and coefficient of variation
  5. This checks for the electronic shuttering and physical motion speed
27
Q

How is the whole body count rate variation tested and what faults does it identify?

A
  1. Use highest sensitivity parallel hole collimator
  2. Attach point source (~100MBq) securely to one of the detector head and run a maximum length wholebody scan
  3. The source should be small enough to avoid motion smoothing effects
  4. Rebin into 64x256 matrix, by resampling it controls the noise
  5. Image reviewed visually and summed profile used to calculate the mean, standard deviation and coefficient of variation
  6. Identifies faults with the digital encoder
28
Q

What are the different method for testing SPECT systems?

A
  • Centre of Rotation
  • SPECT-CT Registration
  • Uniformity
  • SPECT Performance
29
Q

Why do we need to perform a CoR calibration?

A
  • SPECT recontructions require back projection
  • Back projection requires knowledge of how the projection image align with the recontructed image
  • Initial assumption is that the centre of the projection image is the centre of rotation of the camera, this is also the centre of the recontruction matrix
  • This isnt true in reality so CoR calibration must bue performed and the offset applied to recontruct correctly
30
Q

How is the CoR calibrated?

A
  1. Point source suspended in air in the centre
    of the field of view or at a predefined
    offset location
  2. SPECT images acquired, software analysis
    to estimate alignment
  3. Centre of Rotation offsets of up to 1 cm are
    acceptable provided these are corrected
    for (can be done at reconstruction or event
    recording stages)
  4. Offset calibrations will be required for
    various SPECT configurations
  5. Y offset must be well matched in multi-
    head systems –within 2mm
31
Q

What phantoms are commonly used to determine overall SPECT performance?

A
  • Jaszczak Phantom
  • Carlson Phantom
32
Q

What is the test for SPECT Uniformity?

A
  • Using the uniform section of a total performance phantom or remove inserts to produce a cylindtrical uniform phantom
  • Useful to acquire over full FOV, not just a few slices with in the total performance phantom
  • Can be seen as a ring pattern of non-uniformity
33
Q

What is the test for SPECT-CT registration?

A
  1. Using a phantom with hotspots and CT attenuating features so that the SPECT and CT features can be visualised
  2. Mis-registration of more than a few mm should be addressed by recalibration of the camera by a service engineer
34
Q

What is the difference between remedial and suspension levels?

A
  • Remedial levels indiate perfomance that is outside f th enormal range but is accpetable for continued use whilst th eissue is investigated/rectified
  • Suspension levels indicate when the equipmnet is deemed unsuitable for routine use
35
Q

Who determined the remedial and suspension levels?

A

The Medical Physics Expert define the criteria for acceptable performace for all QC tests.

36
Q

What should you do if you identify a fault?

A
  • REPEAT the test only once after checking the test set-up
  • Check for any possible contamination
  • Check the background reading
  • Check the surrounding if the is anything nearby that could cause scatter
37
Q
A

Y2 Nuclear Medicine - MPY8009 (11 decks)

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