Medical Physics Exam 1 Questions with Well
Solved Solutions.
Colloquially: If you add two (or more) signals together and then put them through the
system, you'll get the same result as putting each signal through the system individually
and then adding the result. - Correct Answer-Linear Systems
• What does it mean for a system, S, to be shift- invariant?
• Mathematically: • Let (define output of system)
• Let (defineshiftedinput) • ->
• Colloquially: an arbitrary translation to the input results in an identical translation to the
output - Correct Answer-Shift- Invariant
System output to an input point stimulus (i.e., a Dirac delta function) - Correct Answer-
point spread function (PSF)
Mathematically describes a physical blurring process - Correct Answer-convolution
If a system is linear and shift-invariant (LSI) then...
• The output of the system to ANY input is given by convolution with the system's point
spread function (PSF) - Correct Answer-Linear Shift Invariant (LSI)
The spatial frequency describes how many times the signal oscillates over a fixed
distance
• Units are cycles/mm - Correct Answer-Spatial frequency
Basic idea is that a function can be represented as the sum of a bunch of sine waves
(each with a given amplitude, phase, and frequency)
A Fourier Transform tells you the amplitude and phase of sine waves you need to
reproduce a given function - Correct Answer-Fourier Transforms
• Tells you how much the imaging system “dampens" different spatial frequencies
• Image details are "encoded" by high spatial frequencies so the MTF is a measure of
resolution
, • MTF is a FT pair with the PSF - Correct Answer-Modulation Transfer Function (MTF)
• You have high frequency components in the object
being imaged• But you don't sample enough to see them• Those components are
"aliased" to lower frequencies - Correct Answer-Aliasing
• Imagine you have a periodic signal with frequency f
• To be able to reconstruct that signal, your sampling rate should be at least two times f
• fs≥2f - Correct Answer-Nyquist Theorem
A single element of a 2D image - Correct Answer-pixel
A single element of a 3D image stack - Correct Answer-voxel
A series of 2D images that together comprise a 3D image volume - Correct Answer-image
stack
Image slice - A single 2D image among a 3D stack of images - Correct Answer-image
slice
DICOM - Digital Imaging and Communications in Medicine. People usually think of it as a
file format (similar to .jpg or .png) but is actually a set of"communication standards".
Imagine the internetwithout a common communication protocol... - Correct Answer-
DICOM
PACS - Picture Archiving and Communication System. Massive database of medical
images + interface for radiologists to interpret those images - Correct Answer-PACS
Technologist - healthcare professional who operates the imaging devices and produces
images. Note that ultrasound technologists typically prefer the term"sonographer". -
Correct Answer-Technologist
Radiologist - A medical doctor who specialized in interpreting medical images. - Correct
Answer-Radiologist
Solved Solutions.
Colloquially: If you add two (or more) signals together and then put them through the
system, you'll get the same result as putting each signal through the system individually
and then adding the result. - Correct Answer-Linear Systems
• What does it mean for a system, S, to be shift- invariant?
• Mathematically: • Let (define output of system)
• Let (defineshiftedinput) • ->
• Colloquially: an arbitrary translation to the input results in an identical translation to the
output - Correct Answer-Shift- Invariant
System output to an input point stimulus (i.e., a Dirac delta function) - Correct Answer-
point spread function (PSF)
Mathematically describes a physical blurring process - Correct Answer-convolution
If a system is linear and shift-invariant (LSI) then...
• The output of the system to ANY input is given by convolution with the system's point
spread function (PSF) - Correct Answer-Linear Shift Invariant (LSI)
The spatial frequency describes how many times the signal oscillates over a fixed
distance
• Units are cycles/mm - Correct Answer-Spatial frequency
Basic idea is that a function can be represented as the sum of a bunch of sine waves
(each with a given amplitude, phase, and frequency)
A Fourier Transform tells you the amplitude and phase of sine waves you need to
reproduce a given function - Correct Answer-Fourier Transforms
• Tells you how much the imaging system “dampens" different spatial frequencies
• Image details are "encoded" by high spatial frequencies so the MTF is a measure of
resolution
, • MTF is a FT pair with the PSF - Correct Answer-Modulation Transfer Function (MTF)
• You have high frequency components in the object
being imaged• But you don't sample enough to see them• Those components are
"aliased" to lower frequencies - Correct Answer-Aliasing
• Imagine you have a periodic signal with frequency f
• To be able to reconstruct that signal, your sampling rate should be at least two times f
• fs≥2f - Correct Answer-Nyquist Theorem
A single element of a 2D image - Correct Answer-pixel
A single element of a 3D image stack - Correct Answer-voxel
A series of 2D images that together comprise a 3D image volume - Correct Answer-image
stack
Image slice - A single 2D image among a 3D stack of images - Correct Answer-image
slice
DICOM - Digital Imaging and Communications in Medicine. People usually think of it as a
file format (similar to .jpg or .png) but is actually a set of"communication standards".
Imagine the internetwithout a common communication protocol... - Correct Answer-
DICOM
PACS - Picture Archiving and Communication System. Massive database of medical
images + interface for radiologists to interpret those images - Correct Answer-PACS
Technologist - healthcare professional who operates the imaging devices and produces
images. Note that ultrasound technologists typically prefer the term"sonographer". -
Correct Answer-Technologist
Radiologist - A medical doctor who specialized in interpreting medical images. - Correct
Answer-Radiologist
