Planar NM Imaging Flashcards
used to generate the digital information
Analog to digital converters
A typical NM matrix size is
128 × 128
matrix size may be used for cardiac imaging
64 × 64
matrix size may be used for whole-body imaging
1,024 × 1,024
The number of counts in each pixel in a NM image is stored using a ____
two- byte memory
The counts in images can vary over a wide range, with a median value of
500,000
are usually recorded in a series of short acquisitions lasting only a few dozen milliseconds and make use of the patient’s ECG signal
Cardiac studies
provides computed tomographic views of the three-dimensional distribution of radioisotopes in the body
Single photon emission computed
tomography (SPECT)
are commonly used for SPECT imaging
Parallel-hole collimators
Scintillation cameras rotate ____degrees around the patient
180 or 360
Projection images are obtained at selected angles, typically every ___ degrees.
3 or 6
In SPECT, each projection takes ___ seconds with a total scan time of ____
minutes.
30, 15
Cardiac SPECT images make use of a ___ matrix size.
64 × 64
Noncardiac SPECT imaging likely uses a ____ matrix size.
128 × 128
In cardiac SPECT, at each camera angle there will be ___ projections, with each
projection containing 64 data points, permitting reconstruction of ___ tomographs.
64, 64
SPECT generates an ____ that permits transverse, sagittal, and coronal views to be generated.
isotropic volume data set
were originally used as inputs for filtered-back projection reconstruction algorithms to compute tomographic images.
Scan projections
Iterative reconstruction is more
___ and ___
accurate, minimizes artifacts
SPECT generates an isotropic volume data set that permits ____ views to be
generated.
transverse, sagittal, and coronal
are used to increase system sensitivity and reduce scan times.
Multiheaded cameras
The major benefit of SPECT is the ____ that results from the elimination of overlapping structures.
improved contrast
Multiheaded cameras are used ___ and ____
to increase system sensitivity,
reduce scan times
The use of ____ (i.e., body contouring) for scintillation camera traveling around the patient allows the distance to the patient to be minimized.
elliptical orbits
Most SPECT equipment uses ____ scintillation camera heads.
two
SPECT studies are also performed with
– 111In octreotide for neuroendocrine imaging
– 111In labeled ProstaScint for prostate imaging
– 67Ga for infections
A ____ system contains separate SPECT and x-ray CT imaging systems, with a patient bed passing through both systems.
SPECT/CT
• A ____ contains rings of detectors (scintillators) surrounding the patient.
PET camera
Most early-generation PET scanners had detectors made of
bismuth germanate (BGO)
Modern PET scanners use detectors made of ____or ____
lutetium oxyorthosilicate (LSO)
gadolinium oxyorthosilicate (GSO)
LSO doped with a small amount of yttrium
Lutetium yttrium oxyorthosilicate (LYSO)
have similar gamma ray absorption properties
BGO and LSO
is a markedly poorer absorber of 511-keV gamma rays.
GSO
are inorganic scintillators that emit more light than BGO
GSO and LSO
emit their light much faster than those of BGO.
Organic scintillators
There are three types of coincidences:
a. True coincidences
b. Scatter coincidences
c. Random (accidental) coincidences
produces an output whenever two events are recorded within a specified coincidence timing window.
ACD
ACD produces an output whenever two events are recorded within a specified coincidence timing window. Generically, any such events are called
prompt coincidences
A true coincidence is the simultaneous
detection of two ___ annihilation photons
511-keV
(also called accidental coincidences) occur when annihilation photons from two unrelated positron annihilation events are detected in two different detectors, within the coincidence timing window, and recorded as a single coincidence event.
Random coincidences
This can happen if one photon from each annihilation event is detected in each detector element.
Random coincidences
Line of response data are used to create a ____, which may be reconstructed using filtered back
projection algorithms (i.e., as in CT).
sinogram
was popular in the early days of PET but is now rarely used.
Filtered back projection
____images typically have several million counts.
____ can identify the location of an annihilation event with an
uncertainty that corresponds to a Full Width Half Maximum of ~7.5 cm.
TOF PET
____ information can be used in the reconstruction process to improve
image quality including improved spatial resolution as well as
enhanced lesion contrast.
TOF
most common positron emitter used for PET imaging is
18F(T1/2 =110 minutes)
PET systems have rings that extend over an axial length up to ___ , which permit several transverse image slices
to be simultaneously acquired.
22 cm
may be used to define planes
and limit the number of coincidence counts (2D mode).
Shadow shields (septa)
In ___ mode, coincidences are detected within each individual ring of detectors, or between adjacent rings.
In ___ mode, septal collimator rings are not used and coincidences are detected among many or all rings of detectors.
3D
can accurately rebin 3D data into 2D data sets.
FORE (Fourier rebinning)
PET/CT systems normally offer a ____ gantry aperture.
70-cm
Activity (18F) in PET is typically ____(15 mCi) and is administered ____ minutes before imaging is to
commence.
555 MBq , 60 to 90
____ scans may be performed for attenuation correction only (e.g., 40–80 mAs).
Low-dose CT
____ can be used to generate diagnostic images (e.g., 150–200 mAs)
High-dose CT scans
____ CT scanners are adequate for most PET/CT applications.
Sixteen-slice
______ scanners are targeted for cardiac applications
Sixty-four-slice
Spiral CT scanning from the eyes to the upper thigh can be performed in ____
15 to 20 s
Axial coverage in PET is ____
15 cm to 22 cm
____ is primarily used for staging of malignant disease to monitor patient response to therapy.
PET/CT
