Instrumentation - Gamma Camera QC
a single projection in step-and-shoot mode.
A Stop in a SPECT study is:
pixel
A _________ is a single unit or picture element of a 2D image.
2D image, and is NOT tomographic
A planar image is ___D, and is _______ tomographic.
Uniformity Center of Rotation errors Head-tilt errors
A ring artifact is a problem with camera _____________.
bull's eye artifact
A ring artifact is also known as a __________________ artifact.
Ramp filter Chang attenuation correction
A uniformity image with a thickness of four slices is reconstructed using what 2 things?
5%
A uniformity value of _______% can cause significant ring artifacts.
Voxel
A volume element of a 3D image matrix is known as a:
3%
According to the AAPM (American Association of Physicists in Medicine), camera uniformity should be corrected to ___ % or better.
Noise
Any undesired fluctuation that appears superimposed on a signal due to electrical variations, the random nature of radioactive decay, variability in detection efficiency, and/or variability associated with assigning counts to pixels in an image matrix is known as:
Yes, as spatial linearity is the ability of a scintillation camera to produce a uniform image with straight lines corresponding to straight lines in a phantom.
Can you measure Spatial Linearity with a PLES phantom?
A 2D grid of squares known as pixels, into which image information (example- accepted counts) is placed to create a digital image.
Define an image matrix.
The component of spatial resolution of a gamma camera that can be attributed to the collimator.
Define collimator resolution.
A radiation entity, such as a photon, that has been detected by a radiation-detecting instrument and meets the criteria of the instrument (such as being within the energy window set by the pulse height analyzer).
Define count.
Low energy, parallel hole
Extrinsic Uniformity uses which collimator type?
Co-57 sealed sheet source 99mTc- refillable sheet source
Extrinsic uniformity uses what radiation source?
air bubbles in the field of view
Fillable flood phantom artifacts can be caused by:
Extrinsic
For gamma cameras, a collimator installed between the radiation source and the scintillation crystal is known as:
500,000
How many counts should be acquired in each 2D projection when testing Uniformity?
120 million counts for a 128x128 matrix 30-60 million counts for a 64x64 matrix *Note that 128x128 is the recommended matrix
How many counts should you collect for Uniformity?
Four different widths Four images, acquired at 90 degrees to one another
How many different widths of lead bars and spices are used, and how many images are taken when using the Four Quadrant Bar Phantom for spatial resolution?
3 different widths Multiple images using the minimum bar spacing
How many different widths of lead bars and spices are used, and how many images are taken when using the Hine-Duley phantom for spatial resolution?
IF All holes are equal diameter arranged at right angles to one another. Only one image is needed. IF a circle of pie-shaped wedges set at different intervals is used Multiple images are required, placing the wedge with the smallest spacing over each portion of the crystal
How many different widths of lead bars and spices are used, and how many images are taken when using the Orthogonal hole phantom for spatial resolution?
all bars and spaces are equal width Two images acquired at 90 degrees to one another
How many different widths of lead bars and spices are used, and how many images are taken when using the Parallel-line Equal Space (PLES) Phantom for spatial resolution?
photopenic In the image, the arrows are pointing to photopenic areas of the image.
If an image is showing fewer counts in one area that the other areas, or fewer counts than it should be showing, then it is known as
Isotropic
If the radiation flux from a point source emits photons uniform in all directions, it is called:
call for service, a PMT has failed
If you have a circular cool OR hot area, larger than the diameter of a PMT, you should:
auto-tune the camera, or request service, as you have a mis-tuned PMT
If you have a circular cool area, larger than an actual PMT, you should:
call for service, your crystal may be broken In the image: A- broken crystal B- fillable flood phantom, air bubble C- Poor PMT coupling D- damaged collimator septa
If you have cold spiderweb defects, or cold spots with a hot edge, you should:
a collimator defect. replace or rebore the collimator The image is showing damage to the collimator pushing septa together
If you have cold spots with a hot edge, the problem is most likely:
call for service, your crystal got wet
If you have dark measles, you should:
select the correct peak or adjust the photopeak.
If you have hot or cold tubes, to correct you should:
call for service, your X,Y axis are misaligned
If your image is misshapen, you must:
Average
Information density in gamma camera imaging is the _____ of counts per unit area in a defined region of an image, usually expressed as cts/cm or cts/pixel.
1-5%
Integral uniformity should be:
Point or line source, with 99mTc
Intrinsic uniformity uses what radiation source?
No collimator
Intrinsic uniformity uses which collimator type?
Yes
Is the information in the third dimension included in the planar image?
5%
Planar images can be interpreted with uniformity as high as _____%.
Intrinsic
Quality Control testing done for gamma cameras without a collimator are called:
small and/or centrally located
Ring artifacts will be most noticeable when non-uniformity is _________ or ____________ located.
<3%
SPECT Uniformity is best at:
2-3%
SPECT images suffer degradation when planar uniformity exceeds ____________.
Monthly
SPECT uniformity correction testing should be done:
Uniformity
Sensitivity can be measured simultaneously with __________ if the actvity of the source and the room background are known.
detect ionizing events
Sensitivity is the ability to _________ __________ __________ in a sodium iodide crystal expressed in counts per second per microcurie.
Measured count rate to activity available
Sensitivity is the ratio of:
absorption
Septa are designed to be sufficient to cause the ___________ of the gamma ray.
along with spatial resolution, by examining the straightness of a set of parallel bars, or if using an orthogonal-hole phantom, the straightness of parallel rows of holes.
Spatial linearity is usually assessed:
the ability of an imaging instrument to visualize small objects. the ability to reproduce the details of a nonuniform source of gamma rays.
Spatial resolution is defined as:
Septal penetration Reconstruction using the back projection process
Star artifacts are caused by:
20%
Studies have shown that 1% planar non-uniformity can generate as much as ___% non-uniformity in reconstructed images.
improper photopeak adjustment
Sudden changes in spatial resolution from day to day are usually caused by:
improper photopeak adjustment
Sudden changes in uniformity from day to day are usually caused by:
intrinsic and extrinsic
System resolution combines ________ and _________ resolution.
True
T/F You can use a gallon-size bleach bottle for Uniformity testing.
True
T/F- A scintillator is any material that can release visible-light or ultraviolet photons when an electron moves from a higher-energy orbital to a lower-energy orbital.
True
T/F. Tomography is an imaging process that provides images in multiple slices of the body.
128x128
The AAPM test for uniformity images the phantom using a ____________ matrix.
Projection
The external view of the body from a particular angle that is used to reconstruct a 3D representation of radioactivity in the body is called a:
sineogram
The graph showing the location of the source or the offset vs the view number in a SPECT COR test is called a:
Septa
The lead found between holes in a gamma camera collimator are called:
Septal penetration
The penetration of a gamma ray through a septum of a collimator is called:
Peaking
The process of matching the energy window to the observed energy peak of the gamma ray being imaged is known as:
10-15mCi
To test Uniformity using a gallon-size bleach bottle, add _______mCi of 99mTc diluted with water to fill the bottle.
incompleteness, specifically not including the entire body when acquiring a transmission image set that is to be used for attenuation correction.
Truncation means:
the ability of a gamma camera to produce a uniform image in response to a uniform source of gamma rays.
Uniformity is defined as:
Quarterly
Uniformity testing of floods with other radionuclides should be done:
Daily
Uniformity testing should be done:
Off peak Poor uniformity A wide window in the Pulse height analyzer Increased distance between source and detector Using very low energies Using high sensitivity collimators Your crystal is old
What can decrease your spatial resolution (7 things)?
Using the wrong bar phantom Using High sensitivity, medium/high energy collimators When the width of the bars approaches the collimator's hole diameter An area covered by individual pixels is too big
What creates Moire patterns?
The ability of a radiation detection instrument to respond to variable quantities in a linear fashion, usually over several orders of magnitude (example- activity linearity of a dose calibrator or energy linearity of a scintillation detector In a gamma camera, Linearity is the ability to reproduce a radiation distribution consisting of straight lines, such as a bar phantom.
What is Linearity?
A QC tool used mainly with gamma cameras, often providing some kind of test pattern that is evaluated on the resulting image.
What is a Phantom?
A part of an imaging system that restricts and/or directs gamma rays
What is a collimator?
The number of pixels in each direction of an image matrix; common matrix dimensions are: 64x64 (coarse) 128x128 256x256 (fine)
What is a matrix dimension?
An error in the representation of information, such as an image, that is due to the equipment or technique, rather than an actual difference in the underlying object
What is an Artifact?
For a SPECT study, the amount of correction needed to align the image matrix's center of rotation with the physical axis of rotation.
What is the Offset?
The manner in which a gamma camera rotates in a SPECT acquisition, including the mode of rotation (continuous or stop and shoot), the shape of the orbit, the total angle of rotation, and the number of projections required.
What is the Orbit?
5%
What is the action level for Uniformity Testing?
An image of a uniform distribution of radioactivity
What is the definition of a flood image?
Integral Uniformity: (Max Count Pixel - Min Count Pixel)/ (Max Count Pixel + Min Count Pixel), and multiply by 100. Integral uniformity looks at ALL picels in UFOV or CFOV. Differential Uniformity uses the same formula, but looks at pixels in groups of 5 consecutive pixels.
What is the difference between Integral Uniformity and Differential Uniformity?
QA refers to the processes that determine if an organization is accomplishing its intended functions. QC refers to the procedures and tests used to measure and determine appropriate function of equipment.
What is the difference between Quality Assurance and Quality Control?
A sineogram is a graph showing offset vs view number for a SPECT COR test. A sinogram is an actual image that is created by taking the same row of image data from each projection and putting them into an image matrix used to evaluate for patient motion.
What is the difference between a Sineogram and a Sinogram?
The useful imaging area of an imaging device, usually measured in cm or inches along one or two axis'.
What is the field of view?
Camera non-uniformities
What is the most common source of ring artifacts?
The peak in the energy spectrum of a radionuclide that corresponds to a specific gamma ray emission.
What is the photopeak?
Hine-Duley Four quadrant bar phantom Parallel-line, equal space (PLES) phantom Orthogonal hole phantom
What phantoms can be used to measure spatial resolution of a scintillation camera?
Re-acquire a high count uniformity correction map
What should you do at the action level of 5% for Uniformity Testing?
Spatial resolution Spatial linearity SPECT COR
What tests should be done Weekly?
Water filled plexiglass phantom with 10-15mCi of 99mTc added. Co-57 sheet source
When doing Extrinsic Uniformity testing, what are your radioactivity source options?
20,000 cps
When doing Intrinsic Uniformity testing, you should not exceed __________ counts per second.
5 UFOV
When doing Intrinsic uniformity testing, the point source should be placed ____ UFOV's away from the camera face.
By department policy and camera manufacturers recommendations, usually weekly, monthly or quarterly
When should Intrinsic Uniformity testing be done?
Extrinsic. Intrinsic does not have to deal with the collimator, and so more photons would reach the crystal.
Which Uniformity % would tend to be higher, Extrinsic or Intrinsic?
Scatter
_______________ is the redirection of a gamma ray following a Compton interaction.
