prelims Flashcards
1
Q
Process in which diff tissue attenuation values are averaged to produce one less accurate pixel reading is called
A
Volume Averaging
2
Q
In CT scan the IR is called
A
Detector
3
Q
Method of acquiring and reconstructing the image of a thin cross section on the basis of measurements of attenuation
A
CT
4
Q
Tomos means
A
Slice
5
Q
Tube moves while the IR moves synchronously in CT (T or F)
A
T
6
Q
Other terms used for body-section radiography (BSR)
A
*Laminography
*Planigraphy
*Stratigraphy
*Zonography
7
Q
Primary data (xray photons received by detectors) is converted into
A
Raw data
8
Q
Imaginary pivot point about which the xray tube and IR move. Lies in the object plane
A
Fulcrum
9
Q
Clearest image in CT scan is the
A
Central part of the image, not blurred. Compared to side
10
Q
If anatomy is further from the focal plane (or fulcrum)β¦
A
The more blurred the image is
11
Q
Is the actual distance traversed by the X-ray tube during tomographic movement.
A
Amplitude or tomographic angle
12
Q
Anatomy must be in DFOV, known as
A
Display Field of View
13
Q
It determines the section thickness, which is the thickness of the tissue that will not be blurred.
A
Amplitude
14
Q
The ____ the tomographic angle, the more blurred the images of the structure above and below the object plane.
A
larger
15
Q
Larger tomographic angle, small thickness cut. Small tomographic angle, ___
A
Large thickness cut (Inverse)
16
Q
Blurring motion: unidirectional is___
A
only a linear direction
17
Q
Blurring motion: Pluridirectional is__
A
many different directions
18
Q
Inventor of Clinical tomography
A
Dr. Godfrey Newbold Hounsfield
19
Q
Air used in pneumoencephalography
A
Xenon gas
20
Q
____ units determines the attenuation of Xray in the object using CT
A
HU. Hounsfield Unit
21
Q
CT is a digital image processing because it__
A
Converts xray photons to electric signal (analog data) to numeric data (digital data) for input into a digital computer, to be processed and manipulated to create output image
22
Q
What is Image reconstruction?
A
23
Q
In CT, image is processed or edited through Windowing. What is this?
A
Process of changing the CT image gray scale. Grey-level mapping, or contrast stretching
24
Q
Beam of xray in CT is highly _____ into a thin beam that only passes through cross section of tissue.
A
collimated
25
In CT we do_____ (equivalent of scout film) to image patient before examination to collimate the part.
Scanogram. This is AP and Lateral image of body
26
Lowest kVp used in CT per image is
120kVp
27
Advantages of CT
*Improve image contrast
*Minimal superimposition
*Record of very small differences in tissue contrast
28
Detectors in CT are quantitative and measure small diff. In contrast. Data from detectors are processed by digital computer that uses ___ to reconstruct image.
Algorithm (analog data, binary numbers)
29
Involves physics and mathematical concepts to understand product of image
Physical principles
30
What are the three processes in the physical principle and technology of CT?
*Data Acquisition
*Data Processing
*Image Display
31
What is systemic collection of information from the patient to produce the CT image?
Data Acquisition
32
2 methods of data acquisition in CT
*Slice by slice
*Volume data acquisition
33
In Data Acquisition, data are collected through different beam geometries to scan the pt. Tube rotates around the pt and collect data from the first slice
Slice by slice DATA Acquisition
34
Special beam geometry used to scan a volume of tissue rather than 1 slice at a time. Generates single slice revolution.
Volume DATA Acquisition
35
Generates multiple slices/revolution of X-ray tube
Multislice spiral/helical CT
36
What is convolution in CT imaging?
37
Formula for Relative Transmission
Intensity at source/ intensity at the detectors
38
Formula for Total number of transmission measurements
Number of view (number of rays in each view)
39
Method wherein the xray tube and detectors are arranged to collect transmission or penetration measurements
Data acquisition geometries. There are two types.
40
Xray tube and detectors are couples and rotate 360 degrees around the pt
Continues Rotation
41
Xray tube rotates 360 and is positioned inside a stationary ring of detectors.
Stationary detectors
42
The three steps of this process are raw data processing, image construction, and image storage.
Data Processing
43
Corrections are made and some reformatting of data occurs in this process
Raw data processing
44
Scan data, w/c represent attenuation readings are converted into a digital image characterized by CT numbers
Image reconstruction. Reconstruction techniques or reconstruction algorithms
45
Reconstructed image is held in a disk memory as short term storage. This is___
Image storage
46
Each pixel is assigned by a number. Composed of matrix of pixels, with each pixel representing a volume of tissue (voxel)
CT number. This is related to linear attenuation coefficient (u) of the tissues that comprise the slice
47
What is Matrix?
48
CT number formula?
(ππ‘-ππ€/ππ€) k
ππ‘ = attenuation coefficient of the measured tissue
ππ€ = attenuation coefficient of water
πΎ = contrast factor or scaling factor or constant (1000)
49
CT numbers and attenuation obtained in this factor are referred to as
Hounsfield (H) scale, HU unit
50
CT number for water ____, bone ___, air ____
0, 1000, -1000
51
What is the difference between window width and window level?
*Window width: Contrast. Range of CT number for gray scale (at least 400 levels of gray in HU scale)
*Window Level (or Window Center): Density. Center of the grayscale - density of the image
52
What is bit?
Number of shades of gray in digital imaging
53
CT and energy is (dependent or independent) in linear attenuation
Dependent
54
Reasons why 120kVp is used in CT
*To reduce the dependency of attenuation coefficients on photon energy
*To reduce the contrast of bone relative to soft tissues
*To produce a high radiation flux (high amount of radiation) at the detector
55
This is the final step in CT process which involves storage and documentation
Image display
56
What is dynamic range?
Dynamic range in radiography refers to the range of x-ray intensities a detector can differentiate. A high dynamic range allows for the discrimination between small differences in x-ray attenuation.
57
Windowing is____
Process of changing the CT image gray scale
58
In radiography, we have ____ number of bits of grey
8-12 bits (1024 grey levels)
59
___ is composed of pixels. These pixels have volume called voxel.
Matrix
60
___ determines the size and number of pixels displayed on the monitor
Matrix size
61
High pitch, low spatial resolution, low density. High density, high spatial resolution, ___ pitch.
low
62
___ matrix size can produce a resolution close to 512Β² if the displayed field of view (DFOV) is decreased by Β½ so less tissue is represented / pixel.
smaller
63
___ matrix sizes may be useful for pediatrics & biopsy localization because of faster reconstruction time
Smaller
64
____ this is the each square of the image matrix - ranges from 1-10mm on most scanners
Pixel (picture element)
65
Tissue Volume
Voxel (Volume element)
66
Diameter of the reconstructed image. Diameter of the area being imaged
FOV
67
What is the voxel formula?
Voxel=pixel area x slice thickness
68
Pixel Size formula
FOV/matrix size
69
Size of field w/in the gantry opening - also called body calibration
SFOV scanned field of view
70
Determines size of image on monitor & hard copy - determines pixel size when matrix size is constant
Display or Reconstructed Field of View (DFOV)
71
Less DSFOV
smaller pixels (zoomed in)
72
More DSFOV
larger pixel (zoomed out)
73
Advantages of DFOV
*Optimizes lesion detection
*Determines limits of perceived detail
*Must be equal to or less than SFOV
*May be centered or off-centered
*Often too large to correct positioning error
74
for part of interest
DFOV
75
for scanogram (buo)
SFOV
76
proximal and distal side of tube
Collimator
77
There are 2 sets of detectors in CT. Those are
78
2 processes of conversions.
Photon energy to electronic signal
electronic signal to data signal (analog-digital conversion)
79
Digital data undergo some form of preprocessing includes corrections & reformatting data is called
reformatted raw data
80
What is convolution data?
81
____ reconstruct the image of the internal anatomic structures under examination
back-projection reconstruction algorithm
82
Advantages of CT
*Low contrast is possible
*Contrast Scale
*Volume Data-improve 3d imaging
*Image modification
83
What are the limitations of CT?
*Poor resolution
*High dose
*Limited to axial slices
*Soft tissues surrounded by large amount of bone is difficult to image
*Presence of metallic objects produces streaks
84
Method by w/c patient is scanned to obtain enough data for image reconstruction
Data acquisition (gantry to computer)
85
Defined by beam geometry, which characterizes the particular CT system & also plays a central role in spatial resolution & artifact production
Scanning
86
Size, shape & motion of the beam & its path
Beam Geometry
87
Part of the x-ray beam that falls onto the detector
Ray
88
Collection of the x-ray beam for one translation across the object generate profile
View. View generates the profile
89
Generation of profile
It includes parameters, slice thickness, pt information, and others, displayed in the monitor.
90
X-ray tube & detector move across the object in a straight line when the source-detector assembly makes one sweep across the patient
Translation
91
What are the scanning geometries?
*1st gen (rectilinear pencil beam)
*2nd gen (rectilinear multiple pencil beam scanning)
*3rd gen (continuously rotating fan beam scanning)
*4th gen (Stationary ring 360)
- 5th gen (Encircles pt, Fan beam of xrays)
- 6th gen (Scanning in Spiral-Helical Geometry)
- 7th gen (multiple detector array)
92
- Scanned heads only
- Parallel gray geometry
- Pencil-thin
- 4.5-5min scan time/ slice
- 2 detectors
1st Gen (rectilinear pencil beam)
93
6 of 30 detectors (180 degrees).
Scan time 10-90 secs
fan-shaped xray beam
Whole body, the rest of generation
2nd Gen (rectilinear multiple pencil beam scanning)
94
360 rotation (clockwise, then counter-clockwise) rotate-rotate motion.
Fan shaped.
250-500 detectors.
1-12 secs
various scanning arcs available (half scan, full scan
3rd Gen
95
600-2000 detectors in stationary ring.
360 rotation, half, full and over scan.
1-2 secs scan time.
4th Gen Scanners
96
What are the types of beam geometries in 4th gen scanners?
*Rotating fan beam w/in circular detector array - Fan beam lumalabas
*Rotating fan beam outside a nutating (tilting action of the detector ring during data acquisition) detector ring - Not manufactured, only proposed, Eliminate poor geometry.
97
CT Scanning in Spiral-Helical Geometry (data collected in volume) is based on _____ w/c shortens the high tension cables to the x-ray tube to allow continuous rotation of gantry
Slip-ring technology
98
Geometry system: distance between the x-ray tube & patient at the isocenter is shorter result in improved x-ray efficiency & more photons are available for image production concentration of photons/unit area increases and image blur increases
Short Geometry system
99
Geometry System: necessary to improve image blur & decrease radiation dose external dimensions of the gantry must be increase?
Long geometry system.
100
- classified as high-speed CT-scanners because they can acquire scan data in msec. - electron beam CT scanner (EBCT) & the dynamic spatial reconstructor scanner
- no moving part
- beam: cone-like structure, electronically steered.
- Data acquisition is fan-beam
5th generation Scanners
101
Highly specialized 5th generation, high speed scanner capable of producing dynamic three-dimensional (3D) images of volumes of the patient
dynamic spatial reconstructor (DSR)
102
- Volume rather than slices
- Slip-ring tech
- Single-breath hold
- Less contrast agent used
- Short scan time
- most recent develop in CT data acquisition
Sixth-Generation (CT Scanning in Spiral-Helical Geometry)
103
- use several, closely spaced, complete detector arrays
- no table translation (nonhelical translation)
- each detector array acquires a separate axial CT image
Seventh-Generation: Multiple Detector Array
104
Primary types of acquisition geometries?
- Parallel beam
- Fan beam
- Spiral beam
105
each transmission element
data sample
106
conductive rings form concentric circle in the plane of rotationβ
disc
107
- conductive rings position along axis of rotation to form a cylinder
- the brushes that transit electrical power to CT components glide in contact grooves on the stationary slip ringβ
cylindric
108
2 common brush designs
wire brush
composite brush
109
- uses conductive wire as a sliding contact
- 2 brushes per ring are often
wire brush
110
uses a block of some conductive material (silver graphite alloy) as a sliding contact
composite brush
111
- AC power and xray control signals are transmitted to slip rings by means of low
- voltage brushes that glide in contact grooves on
low-voltage slip ring
112
- AC delivers power to the high voltage generator, w/c subsequently supplies high voltage to the slip ringβ
- is transferred to x-ray tube
high voltage slip ring
113
this step is characterized by the beam geometry & method of scanning & involves the passage of x-rays through the patient
sequence of data acquisition
114
