PRELIM Flashcards
1
Q
Prior to CT there was:
A
2D imaging was used xrays
There was superimposition of structures
Less clarity of images
2
Q
use of computer
A
computed
3
Q
Greek word “_____” means slice, “____” means
write
A
tomos
graphy
4
Q
is the process of generating a two dimensional image of a slice or section through a 3 dimensional (3D) object ( a tomogram)
A
Computed tomography
5
Q
is an examination that uses xray and computers to obtain a cross sectional image of the human body
A
computed axial tomography
6
Q
The first commercially CT Scanner was invented by
A
Sir Godfrey Hounsfield
in Hayes, United Kingdom
at EMI Central
Research Laboratories using xrays.
7
Q
The first EMI scanner was installed in
A
Atkinson Morley
Hospital in Wimbledon, England
8
Q
The 1st patient brain- scan was done on
A
October 1, 1971
9
Q
is limited to scanning only brain
A
EMI (Electric and Musical Industries Limited) Scanner
10
Q
got their 1979 Nobel Prize for their
contributions to CT (medicine and physiology)
A
Hounsfield and Cormack
11
Q
theoretical calculations on xray was
used by Hounsfield
A
Allan Mcleod Cormack’s
12
Q
PARTS OF CT
A
- Gantry(Scanner System)
- Patient’s table
- Computer ( Operation Control)
13
Q
Part of Gantry
A
Xray tube
Detector system
Collimators
Filters
14
Q
generates xray beams
A
Xray tube
15
Q
detects the xray passing through the
patients body
A
Detector system
16
Q
narrows the beams of xray
A
Collimators
17
Q
These are used to filter some rays from
entering the patient’s body that may be harmful
A
Filters
18
Q
2 types of gantry
A
Conventional
Spiral Scan
19
Q
scan is taken slice by slice and after the scan stops (e.g from the top of abdomen till pelvi this needs the patient to hold their breath.
A
Conventional
20
Q
continuous scan taken in spiral fashion. It is quick.
A
Spiral Scan
21
Q
separation
A
Nuclear fission
22
Q
fused
A
Nuclear Fusion
23
Q
When x-ray pass through the human body some of the xray _________________________-
A
are absorbed and some pass through the body to produce an image.
24
Q
the film directly absorbs penetrate xrays, measures the xray amount, and transmits the data to a computer system.
A
plain xray imaging
25
calculates and analyzes data from each detectors in each level, and finally reconstructs multiple, two dimensional, cross- sectional image.
computer system,
26
Displayed on screen
Computer ( Operation Control)
27
Hounsfield scale( linear transformations reference being _____
distilled water
28
Range from _______ (bone) to ________ (air/gas)
+1000
-1000
29
CT number or Hounsfield scale is a measure of
radiodensity
30
CT number measured in ____ unit
HOUNSFIELD
31
CT NUMBER:
BONE
+1,000
32
CT NUMBER:
Liver
40-60
33
CT NUMBER:
White matter
-20 to -30
34
CT NUMBER:
Grey matter
-37 to -45
35
CT NUMBER:
blood
40
36
CT NUMBER:
muscle
10-40
37
CT NUMBER:
Kidney
30
38
CT NUMBER:
CSF (Cerebrospinal fluid)
15
39
CT NUMBER:
water
0
40
CT NUMBER:
fat
-50 to -100
41
CT NUMBER:
air
-1,000
42
was introduced in 1971 limited to axial imaging of the brain in neuroradiology
Clinic CT
43
Clinic CT was introduced in
1917
44
It developed into versatile 3D whole body imaging modality for a wide range of applications in for ex.
- [ ] Oncology, vascular radiology cardiology traumalogy and IR
Clinic CT
45
Computed tomography can be used for
- [ ] Diagnosis and follow ip studies for patients
- [ ] Planning of radiotherapy treatment
- [ ] Screening of healthy subpopulations with specific risk factors
46
Nowadays dedicated scanners are available for special clinical applications , such as
- [ ] For radiotherapy planning these CT scanners
- [ ] The integration of CT scanners
47
multi modality imaging applications for example by integration of CT scanner with a PET Scanner
integration of CT scanners
48
offer an extra wide bore allowing the Ct scans to be made with a large FOV
radiotherapy planning these CT scanners
49
dual source CT scanner
a CT scanner that is equipped with two x-ray tubes
50
volumetric CT scanner
a 320 detector row CT scanner that allows for scanning entire organs within one rotation.
51
is perfectly suited for 3D imaging and used in for example brain cardiac musculoskeletal and whole body CT imaging
Ct scanning
52
The images can be presented as impressive colored 3D rendered images but radiologists usually rely more on black and white 2D images either the 2D axial images or 2D reformats.
Ct scanning
53
The purpose of a ______ is to measure xray transmission through a patient for a large number of views
CT acquisition
54
Different views are achieved in CT primarily by using:
- [ ] Detector with hundreds of detectors elements along the detector arc (generally 800-90p detector elements
- [ ] By rotation of the X-ray tube around the patient, taking about 1,000 angular measurements
- [ ] And by tens or even hundreds of detector rows aligned next to each other along the axis of rotation
- [ ] The values that are assigned to the pixels in a CT image are associated with the average linear attenuation coefficient (m^-1) of the tissue represented within that pixel.
- [ ] The linear attenuation coefficient (y) depends on the composition of the material, the density of the material, and the photon energy as seen in Beer's law:
- [ ] * Beer's law only describes the attenuation of the primary beam and does not take into account the intensity of scattered radiation that is generated.
- [ ] * For poly-energetic X-ray beams Beer’s law should strictly be integrated over all photon energies in the X ray spectrum.
- [ ] In the back projection methodologies developed for CT reconstruction algorithm. this is generally not implemented.
55
Beer's law:
* where I(x) is the intensity of the attenuated X ray beam,
* I0 the unattenuated X ray beam,
* and x the thickness of the material.
56
only describes the attenuation of the primary beam and does not take into account the intensity of scattered radiation that is generated.
Beer's law
57
should strictly be integrated over all photon energies in the X ray spectrum.
poly-energetic X-ray beams Beer’s law
58
Instead typically a pragmatic solution is to assume where Beer's law can be applied using one value representing the average photon energy of the X ray spectrum. This assumption causes inaccuracies in the reconstruction and leads to the beam __
hardening artefact
59
As an X ray beam is transmitted through the patient, different tissues are encountered with different linear attenuation coefficients.
* The intensity of the attenuated X ray beam, transmitted a distance d, can be expressed as:
____-
l(d)=l0e^0
60
is composed of a matrix of pixels representing the average linear attenuation co-efficient in the ass dated volume elements (voxels)
CT image
61
a simplified 4 x 4 matrix representing the measurement of transmission along one line
Illustration:
62
Each element in the matrix can in principle have a different value of the associated linear ___
attenuation coefficint. (Micro sign)
63
The equation for the attenuation can be expressed as: refer to__
pic
64
is transformed into a corresponding matrix units (HUmaterial), where the HU scale is expressed relative to the linear attenuation coefficient of water at room temperature (Uwater):
CT the matrix of reconstructed linear attenuation coefficients (u material)
65
is expressed relative to the linear attenuation coefficient of water at room temperature (Uwater):
HU scale
66
HU water , =
0 as (Umaterial=U water),
67
HU., =
-1000 as (Umaterial = 0)
68
HU=
1 is associated with 0.1% of the linear attenuation coefficient of water.
69
are usually visualized in an 8bit grey scale offering only 128 grey values
Hounsfield units
70
The display is defined using
- [ ] Window level (WL) as CT number of mid grey
- [ ] Window width (WW) as the number of HU from black >> white
71
is dedicated by clinical need
choice of WW and WL
72
can only be achieved by selecting the most appropriate window width and window level.
Optimal visualization of the tissues of interest in the CT image
73
Different settings o the WW and WL are used to visualize for example _____
soft tissue, lurg tissue or bone.
74
for substances and tissues, except for water and air, variations
of the Hounsfield units occur when they are derived at ___
different tube voltages.
75
reason is that as a function of photon energy different substances and tissues exhibit a non linear relationship. of their linear attenuation coefficient relative to water.
different tube voltages.
76
effect is most notable for substances and tissues that have a relatively high (effective) atom number such as contrast enhanced blood (iodine) and bone (calcium).
exhibit a non linear relationship. of their linear attenuation coefficient relative to water.
77
In clinical practice, ___ between the expected and the actually observed Hounsfield unit may occur.
considerable deviations
78
may be the dependence of the Hounsfield unit for example on the reconstruction filter, on the size of the scanned field of view, and on the position within the scanned field of view.
inaccuracies
79
image artefacts may have an effect on the accuracy of the ____
Hounsfield units.
80
CT developed rapidly as an indispensable imaging modality in diagnostic radiology.
early 1970's
81
Most of the modern CT technology that is being used in clinical practice nowadays was already described at the end of the year ___
1983.
82
development of multi detectors- row CT and multi-source CT was described in ___
1980
83
is a simplified plan view.... In which three xray sources are employed in conjunction with three corresponding rotating xray array detectors
figure
84
Currently most scanners are __, multi detector row CTscanners
helical
85
The technologies of ___ have however also been implemented on a wide scale.
dual source and volumetric CT scanning
86
On the rotating part of the gantry are mounted for example
* the xray tube detector the high voltage generator for the xray tube,
the (water or air) cooling of the xray tube, the data acquisition system the collimator and the beam shaping filters
87
is generally supplied to the rotating gantry through contacts (brushes) from stationary slip rings.
Electrical power
88
are transmitted from the gantry to a computer usually by wireless communication (or slip ring contacts).
Projection profiles
