Image production Flashcards
CT differentiation of tissue relies on…
Densities of tissues
X ray production requires 3 things…
Electrons, means of accelerating them, and means of deceleration
how are CT tube different from x ray
thicker anode, faster rotation, higher heat capacity
what does mA control in CT?
Intensity, dose, and exposure
rotation time controls…
intensity, dose, and exposure
what is the disadvantage of increasing rotation time?
lowers resolution
mAs is calculated by
mA x rotation time
what does kVp control?
Energy, Dose, and Penetration
what is the function of detector array?
detecting photons and converting it to electrical signal called attenuation measurement
what does Data Acquisition system do?
it measures the transmitted rad, converts electrical signal, and transmit to raw data
X axis indicates
Right to left
Y Axis indicates
Vertically, anterior to posterior
Z Axis extends
Superior and Inferior
Coronal view changes from Ant to Post which is what axis?
Y Axis
Sagittal view changes from Right to left, which is what axis?
X axis
what is axial scanning?
Slice by slice, it is a non-continuous exposure
Helical scanning is also called
Spiral scanning, the table is in constant motion
what scan technique is used with contrast?
Helical scan, best for contrast enhancement
what is volume scanning?
it is like axial, but it is organ specific. Entire organ is scanned
how would you describe pitch?
pitch is the ratio of table movement to beam width
What are the different values of pitch?
pitch is either greater to 1, 1, or less than 1
When the pitch is greater than 1…
when table moves more than the beam width itself
When pitch is less than 1…
when the table moves shorter than the beam width
what is the advantage of less than 1 pitch
highest spatial resolution, but disadvantage is highest dose and slowest scan
pitch greater than 1 advantage is
it is the fastest scan speed, but lowest spatial resolution
how do you calculate for table movement?
Beamwidth x Pitch
is 1mmx16 rows the same as 2mm x 8 rows and 4mmx4 rows?
Yes
what is the benefit of thin rows ?
higher spatial resolution
thick rows benfits are?
lower pt dose and faster scan
whats wrong with faster scan and less patient dose acquisition thickness adjustment?
decreased spatial resolution
Raw data is also known as
Scan data
what is interpolation?
It is a reconstruction process unique to helical scan, it can be summarize as deduction method.
What is convolution used for? and what are the 2 types?
it is used for reconstruction. Smooth and edge enhancing
Standard algorithm is also known as
Smooth
what is filtered backprojection
projections being compiled back onto each other
what are the 3 steps of reconstruction?
Interpolation, Convolution, and Filtered Backprojection
what are the differences in prospective vs retrospective recon?
time at which it was done, either before or after
Reconstruction slice thickness depends on….
anatomical parts
Chest, Abd, and pelvis are thicker/thinner slices?
Thicker
What’s wrong with thinner slices?
increases image noise
True or false, thick slices must be applied to all, coronal, axial, and sagittal
False, they can be different
When slice interval is equal to thickness
there are no space a part
If slice interval is more than the thickness what would happen?
there would be gap between slices
if slice interval is less thank thickness?
there would be overlapping of information
does changing the window width and level affect Hounsfield Unit?
no
what increases spatial resolution?
recon for thinner slice, smaller detector size, decreasing pitch, increasing rotating time, decreasing DFOV, Decrease acquisition thickness, increasing matrix size
how is spatial resolution measured?
line pairs per centimeters
Does algorithm affect spatial resolution?
yes
When Spatial Resolution is increased.. what can unfortunately happen?
increased image noise
what is contrast resolution?
ability to tell the difference between the anatomy in the area
If image noise increase… what happens to contrast resolution?
decreases contrast resolution
Can algorithm affect contrast resolution?
yes
If you want to increase contrast resolution what can you do?
increase technical factors, avoid scaning big pts, using thicker detector rows, using thick recon slice,
how do you quantify image noise?
by placing ROI in the general area and checking the average HU and Stand. Dev
what is Standard deviation also known as?
Image noise
Ability of scanner to produce still images of objects in motion describes…
Temporal resolution
what increases temporal resolution?
increasing scan speed
what are the quality control tests?
spatial res, contrast resolution test, Image noise, Accuracy of CT numbers, linearity test (as attenuation incr, CT number should incr), Uniformity (same CT number in same substance regardless of diff ROI)
