4 Image Quality Flashcards
level of detail that can be seen on an image
Spatial Resolution
How small an object can e seen on a PARTICULAR IMAGING SYSTEM
Limiting Spatial Ressolution
two (in xray) and three (in ct and mri) dimaenions of a single image
spatial dimesion
Most asic measure of he esolution properties of an imaging system. Response of the imageing ssystem to the input to theimaging system (point source).
Point Spread function or Impule Response Function
imaging system with the same PSF (Point Spread Function) at all locations in the field of view
Stationary or Shift Invariant Imaging System
versus PSF that vary depending on the position
Nonstationary
FN = 1/2 triangle
Sets the upep bound on the spatial frequecyy that can be detected for a digital detector system with detector pitch (triangle).
Nyquist Frequency
occurs when frequencies higher than the Nyquist frequency are imaged p 73
Aliasing
Ability to detect very subtle changes in gray scale and distinguih them from the noise in the image.
Characterized by the measuements that pertain to the signal-to-noise ratio in in image
Contras Resolution
source of image noise
silver grains
77
Grain noise
source of image noise
happens when electrons associated with noise are added into the signal prior to amplification circuits, thn their noise contibuion will be amplified as well p 78
Electrical noise
Source of image noise
whn gopus of dtector elements that are read out may have different offset noise and gain characteristics
Structure noise
——- image is mesures with no radiation incident on the detector.
These two calibration images then can be used to correct for structured noise using the so called ——–
offset image
field correction algorithm
source of image noise
generated by patent anatomy
Anatomical noise
solution to anatomical noise
- acquires before and afer the injection of fascular contrast agents
- subtracting ribs in the xray
- digital subtraction angiography
2. dual-energy subtraction techniques
conceptual visual method for combining the concepts of spatial resolution and contrast resolution
CD diagram
—– of an imaging system is a characterization of an xray imaging system used by imaging scientists, which describes overall frequency-dependent SNR performance of the system.
It is the ratio of SNR squared output from the systems to the SNR squared of the signal input into the system
Detective Quantum Efficiency
fundamental contrast that arises from the signal AFTER it has interacted with the patient but before it has been detected.
Subject contrast
actual anatomical or funtional changes in patient’s tissues
intrinsic component
relates to how the image-acquisition protocol can be optimized to enhance subject contrast.
example, gadolinium in MR and iodine in CT
Extrinsic factors of
detector system can have profound impat o nhow the subject contrasst incident
detector contrast
converiton of analog sinal to digital and its two steps
digitization
sampling
quantization
The _____ is an object size-independent measure of the signal
level in the presence of noise. Tm
The contrast-to-noise ratio (CNR)
____ of an imaging system is a characterization of an x-ray imaging system, used by imaging scientists, which describes the overall frequency-dependent SNR performance of the system. In conceptual terms, the _______ can be defined as the ratio of the
SNR2 output from the system to the SNR2 of the signal input into the system
Detective Quantum Efficiency
