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Computed Tomography Questions and
Correct Answers/ Latest Update /
Already Graded
For a typical 64 to 128 detector array CT scanner, the fan angle is
approximately ___ degrees, while the full cone angle is about ___
degrees
Ans: 60, 2.4
CT Fan beam projection diagram
Ans:
CT Cone beam projection diagram
Ans:
CT True cone beam projection diagram
Ans:
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Why is an arc-shaped detector beneficial in CT?
Ans: By mounting the detector modules on a support structure that is
aligned along the radius of curvature emanating from the x-ray source,
there is very little difference in fluence to the detectors due to the inverse
square law. Very importantly, the primary x-rays strike the detector
elements in a nearly normal manner, and so there are effectively no
lateral positioning errors due to x0ray beam parallax
Features of true cone beam systems
Ans: Cone angle nearly as great as the fan angle. Planar flat detector
with a 2D bank of detectors. Correction methods needed for different
distances from source to detector ,giving rise to inverse square and hell
effect-based differences in fluence to deach dexel. Some parallax.
Some uses of true cone beam imaging
Ans: Dental/maxillofacial CT cystems, breast CT systems, radiation
therapy
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Typical true cone beam specifications
Ans: 30x40cm flat panel detector, SSD 90 cm, 25 deg fan angle and 19
degree cone angle
General CT Geometry Diagram
Ans:
Third Generation (Rotate-Rotate) CT Geometry
Ans:
Magnification factor at the CT scanner's isocenter
Ans: M - B/A where B is the SID and A is the source to isocenter distance
Detector dimensions in CT are generally referred to their size as
projected to the _______
Ans: isocenter
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The maximum FOV of a CT is defined by ______
Ans: The physical extent of the curved detector arrays (the fan angle)
If the (minimum) CT slice thickness is quoted on a scanner, the actual
detector width is _______
Ans: Larger by magnification factor M = B/A. That is, for a 0.5 mm min slice
thickness, and B = 95 and A = 50, the actual detector width is 0.95 mm.
That is why most dimensions in CT are related to the plane of the isocenter
Do CT scanners use 2D antiscatter grids?
Ans: Sometimes
CT antiscatter grid diagram
Ans:
CT Tube Orientation Diagram
Computed Tomography Questions and
Correct Answers/ Latest Update /
Already Graded
For a typical 64 to 128 detector array CT scanner, the fan angle is
approximately ___ degrees, while the full cone angle is about ___
degrees
Ans: 60, 2.4
CT Fan beam projection diagram
Ans:
CT Cone beam projection diagram
Ans:
CT True cone beam projection diagram
Ans:
,2 | Page
Why is an arc-shaped detector beneficial in CT?
Ans: By mounting the detector modules on a support structure that is
aligned along the radius of curvature emanating from the x-ray source,
there is very little difference in fluence to the detectors due to the inverse
square law. Very importantly, the primary x-rays strike the detector
elements in a nearly normal manner, and so there are effectively no
lateral positioning errors due to x0ray beam parallax
Features of true cone beam systems
Ans: Cone angle nearly as great as the fan angle. Planar flat detector
with a 2D bank of detectors. Correction methods needed for different
distances from source to detector ,giving rise to inverse square and hell
effect-based differences in fluence to deach dexel. Some parallax.
Some uses of true cone beam imaging
Ans: Dental/maxillofacial CT cystems, breast CT systems, radiation
therapy
,3 | Page
Typical true cone beam specifications
Ans: 30x40cm flat panel detector, SSD 90 cm, 25 deg fan angle and 19
degree cone angle
General CT Geometry Diagram
Ans:
Third Generation (Rotate-Rotate) CT Geometry
Ans:
Magnification factor at the CT scanner's isocenter
Ans: M - B/A where B is the SID and A is the source to isocenter distance
Detector dimensions in CT are generally referred to their size as
projected to the _______
Ans: isocenter
, 4 | Page
The maximum FOV of a CT is defined by ______
Ans: The physical extent of the curved detector arrays (the fan angle)
If the (minimum) CT slice thickness is quoted on a scanner, the actual
detector width is _______
Ans: Larger by magnification factor M = B/A. That is, for a 0.5 mm min slice
thickness, and B = 95 and A = 50, the actual detector width is 0.95 mm.
That is why most dimensions in CT are related to the plane of the isocenter
Do CT scanners use 2D antiscatter grids?
Ans: Sometimes
CT antiscatter grid diagram
Ans:
CT Tube Orientation Diagram
