Computed Tomography in the Diagnostic Radiography Curriculum - PowerPoint PPT Presentation

Loading...

PPT – Computed Tomography in the Diagnostic Radiography Curriculum PowerPoint presentation | free to download - id: 3c32a2-NWI5N



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Computed Tomography in the Diagnostic Radiography Curriculum

Description:

Computed Tomography in the Diagnostic Radiography Curriculum My Disclaimer My position on CT in the Diagnostic Curriculum is that it is more beneficial than harmful. – PowerPoint PPT presentation

Number of Views:299
Avg rating:3.0/5.0
Slides: 122
Provided by: occonline
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Computed Tomography in the Diagnostic Radiography Curriculum


1
Computed Tomography in the Diagnostic Radiography
Curriculum
2
My Disclaimer
  • My position on CT in the Diagnostic Curriculum is
    that it is more beneficial than harmful.
  • I am not suggesting that students graduate from
    our Programs as CT techs.
  • I AM suggesting that they have an understanding
    of the modality, its basic concepts, and focused
    clinical opportunities.

3
The Premise
  • I look at CT within the curriculum as a two-fold
    activity from the student perspective.
  • One, provides students a basic overview of what
    CT is, how it works, and why its better for
    some diagnoses.
  • Two, CT provides an excellent means of review for
    general radiography principles that may be old
    hat for some, boring for others, or just offers a
    different perspective than the original
    explanations.

4
When to Present CT
  • CT has to be in the second year or later. There
    needs to be a foundation of relevance and
    understanding.
  • In our Program, CT is officially taught in the
    Rad T 265 course, first semester second year.
  • Clinical rotations begin in the middle of the
    first semester second year.
  • Unofficially CT is found throughout our second
    year curriculum.

5
  • Radiologic Technology 265
  • Principles of Digital Imaging and Computer
    Applications (2) Prerequisite Radiologic
    Technology 165. Introduction to computer aided
    medical imaging's as used in radiography
    departments. Applications include computed and
    digital radiography (CR/DR), CT, MRI, and other
    modalities. Basic imaging principles are applied,
    including physics, imaging protocols, and systems
    electronics. Software and display strategies for
    varying modalities will be discussed.

6
  • Date Lecture Topic Reading Assignment
  • Aug 28 Orientation/Principles of CT B. Ch 29,
    M v3 Ch 33
  • Sep 4 HOLIDAY
  • Sep 11 Components of a CT scanner
  • Sep 18 Data Acquisition technology B. Ch 30
  • Sep 25 Spiral CT
  • Oct 2 Image reconstruction
  • Oct 9 Image quality
  • Oct 16 Image manipulation M. Ch 36
  • Oct 23 MRI physics and equipment
  • Oct 30 MRI image acquisition M. v. 3 Ch 36
  • Nov 6 Computer literacy and its relevance B. Ch
    26
  • Nov 13 Basic concepts of digital imaging B. Ch
    27, M v3 Ch 34
  • Nov 20 Digital fluoroscopy M v 3 Ch 35, B. Ch
    28
  • Nov 27 Digital fluoroscopy
  • Dec 4 Ultrasound and Nuc. Med. Applications M
    v3 Ch 3738
  • Dec 11 FINAL

7
Why the importance of teaching CT?
  • Provides a break from the regular routine.
  • Offers new technology or info that may be
    exciting.
  • Reviews existing (hopefully) knowledge.
  • For example, Photon/tissue interactions
  • Great way to review anatomy and pathology as seen
    clinically.
  • Provides an excellent opportunity to experience a
    modality first hand.

8
The Clinical Component
  • We began a clinical affiliation this year with a
    free-standing imaging center.
  • Last year, we had an observational agreement that
    allowed students to visit and only watch.
  • This year students have clinical expectations
    based on the time they spend there.

9
Clinical continued
  • Students are allowed to pick a three week
    optional rotation.
  • We chose this in order to have students doing
    something that interested them thereby decreasing
    the possibility of discontent.
  • Also, students looking for additional education,
    therapy or nuclear medicine, could get their
    observational requirements met.

10
The Proposed CT Curriculum
  • CT Generations
  • Components, Operations, and Processes
  • Radiation Protection Practices

11
CT Generations
  • This is really the only area that has limited
    value in the diagnostic curriculum.

12
First and Second Generation CT
  • The first and second generations of CT were very
    similar.
  • Both used a scanning technique called
    translate/rotate in order to move around the
    patient.
  • The first generation scanner used a single
    detector and thin beam. While the second
    generation scanner use several detectors and a
    fan beam.
  • These changes resulted in a significantly faster
    scanner.

13
Third Generation
  • The big change here was that the tube was in
    constant motion throughout the exposure, no more
    stops and starts.
  • The detectors were also moving during the
    exposure and more detectors were added.
  • As before, we now have an even faster scanner.

14
Fourth Generation
  • It became obvious that moving detectors
    introduces noise into the image.
  • Now the detectors are fixed in a ring around the
    patient and only the tube moves.
  • Thousands of detectors are now needed to generate
    an image.
  • Faster imaging with increased spatial resolution.

15
Fifth Generation
  • Electron beam CT
  • EBCT
  • Ultrafast

16
Spiral
  • Slip-ring technology eliminates power cables.
  • Constant power to moving tube.
  • Continuous exposure
  • Patient moves through the beam during exposure
  • A stream a data is generated (spiral) as opposed
    to a series of individual slices.

17
  • CT scanner generations have limited value outside
    of understanding CT. However, it does provide a
    mechanism to see the development of a modality.
  • Additionally, the advantages of each generation
    and its evolution illustrates the thought
    processes that go into learning and adapting.

18
Components, Operations, and Processes
  • Most of these topics have direct correlation to
    diagnostic radiography.
  • Data acquisition
  • Factors controlling image appearance
  • Anatomical structures
  • Post-processing

19
Data Acquisition
  • Methods
  • Slice by slice
  • Contiguous
  • Volumetric
  • Spiral/helical

20
Beam Geometry
  • Parallel
  • Fan
  • The traditional beam geometry, it is opened along
    the width of the patient.
  • Spiral
  • The beam is continuously on allowing for more
    anatomical coverage in a shorter time.

21
Data Acquisition system (DAS)Components
  • Tube
  • Detectors
  • Filters
  • Collimators
  • ADC

22
CT Tubes
  • Much higher heat loading than conventional tubes
  • 8MHU and up
  • Generally have two focal spots

23
Filters
  • Again CT filtration is similar to diagnostic
    radiography
  • All tubes are required to have minimum filtration
  • Primary purpose is patient protection
  • Also, in CT the filter is used to harden the
    beam thereby, decreasing absoption
  • Compensating filters
  • Bow-tie
  • Uniform beam intensity at the detectors
  • Think wedge filter in diagnostic radiography.

24
CT Collimators
  • CT consists of both pre and post-patient
    collimation
  • Pre-patient collimation is analogous to the
    collimation we already know.
  • Controls beam coverage or amount of anatomy
    exposed.

25
Post-patient Collimation
  • Controls slice thickness.
  • Additionally, it serves to define the slice
    profile which provides a sort of grid effect.
  • Scatter rejection

26
Analog-to-Digital Convertor (ADC)
  • Converts the analog signal from the detectors to
    a digital signal for processing.
  • Rated by bits
  • Most scanners today are 16-bit systems
  • Produce 4096 data points
  • The more data points, the better the gray scale
    (contrast) resolution.

27
Measurement of the Transmitted Beam
  • A ray
  • Basically, the detected value of a single photon
  • Several rays combine to form a view.
  • The data from multiple photons hitting the
    detector during a single translation.
  • Profile
  • The electrical signal produced by the detector.

28
Encoding into Binary Data
  • The data from the views is converted into
    attenuation coefficients using the formula
  • The attenuation coefficients are then sent to the
    ADC.

1
___
lnIo/I

x
29
Data Transmission to the Computer
  • Data processing begins
  • The raw (detector) data is preprocessed to remove
    bad data sectors.
  • The reformatted raw data is now sent to the array
    processors.
  • The array processors are using filter algorithms
    to produce the desire image appearance, i.e. soft
    tissue, bone, high-res.

30
  • After the array processors, the data is then
    subjected to a reconstruction algorithm that
    produces the cross-sectional image we see.
  • The most common reconstruction algorithm today is
    the filtered back projection.
  • The data is now image data and available for
    image manipulation.

31
The CT Image
  • Any digital image, including CT, is comprised of
    picture elements (pixels).
  • The pixels are 2-dimensional elements that
    represent volume elements (voxels).
  • Pixels are displayed in a matrix.
  • The brightness of each pixel is determined by the
    CT number it represents.

32
CT Numbers
  • CT numbers are calculated by comparing the
    attenuation coefficients of water and tissue.
  • The formula is
  • CT

__
.
__________
t
w
K

w
33
  • The CT number of water is 0.
  • Now, if you look at the formula you can see that
    tissues attenuate more than water will have a
    positive CT number.
  • Conversely, tissues less attenuate less have
    negative CT numbers.

34
Examples of Tissue Attenuation Coefficients and
Their CT Numbers
35
Factors Affecting Attenuation
  • Photon energy
  • Selected kVp
  • Filtration
  • Tissue effective atomic number
  • Tissue mass density

36
Selectable Scan Factors
  • Field of View
  • Scan
  • Display
  • Matrix size
  • Slice thickness
  • Algorithm
  • Scan time and rotational arc

37
  • Tube output
  • mAs
  • Region of Interest (ROI)
  • Magnification
  • FSS and Tube geometry

38
Scan FoV
  • The total area from which raw data is acquired

39
Display FoV
  • Determines how much raw data is used in
    displaying the acquired image.

40
Matrix Size
  • Basically, the number of pixels displayed.
  • Affects spatial resolution
  • The bigger the matrix the more pixels.
  • Given that image size stays the same the pixels
    have to be smaller therefore, spatial resolution
    increases.
  • Generally, the larger the image matrix the higher
    the patient dose.

41
Algorithm
  • Mathematical formula applied to the raw data in
    order to produce a specific image outcome.

42
Scan time and Rotational Arc
43
Radiographic Tube Output
  • mAs

44
ROI
  • Allows the technologist to select a specific area
    of interest for image reconstruction.
  • Uses the raw data for the reconstruction instead
    of using image data
  • The result is a better quality image.

45
Magnification
  • Defined as a post-processing activity.
  • Magnification uses image data not raw data, so
    the final product has less spatial resolution
    than when using ROI.

46
FSS and Tube Geometry
  • FSS
  • In CT, FSS selection has the same connotations it
    has in diagnostic radiography.
  • A smaller FSS has more detail (resolution) than a
    larger one. However, due to digital imaging
    issues (monitor and matrices) the effects of a
    small versus large FSS are not as apparent.

47
Factors Affecting Image Quality
  • Spatial resolution
  • Contrast resolution
  • Noise
  • Radiation dose
  • Artifacts

48
Spatial Resolution
  • The degree of blurring within the image
  • Ability to discriminate objects of varying
    density a small distance apart.
  • CT spatial resolution is affected by
  • Geometric factors
  • Reconstruction algorithm

49
Geometric Factors
  • FSS
  • Detector aperture width
  • Slice thickness
  • SID
  • SOD distance to isocenter
  • Sampling distance
  • Number of projections

50
Reconstruction algorithms
  • Several different types of convolution algorithms
    are available.
  • Edge enhancement
  • Smoothing
  • Soft tissue
  • Bone
  • Matrix size is also going to play a role in
    spatial resolution

51
Potential Spatial Resolution
52
  • Can easily be demonstrated on CR/DR as well as CT
  • Examples here

53
Spatial resolution
  • FoV
  • Amount of anatomy displayed
  • Also an issue with fluoroscopy
  • Affects on patient dose
  • Matrix
  • Affects on spatial resolution and patient dose
  • Pixel
  • Voxel
  • Slice thickness
  • Opportunity to demonstrate partial voluming and
    superimposition

54
Contrast Resolution
  • Affected by several factors
  • Photon flux
  • Slice thickness
  • Patient size
  • Detector sensitivity
  • Reconstruction algorithm
  • Image display
  • noise

55
Photon flux
  • Basically, the number of photons available
  • kVp
  • mAs
  • Beam filtration
  • Patient size also affects photon flux
  • Larger patients attenuate more photons

56
Slice Thickness
  • Slice thickness is controlled by post-patient
    collimation
  • Tight collimation decreases the number of
    scattered photons that can strike the detectors
  • Fewer scatter photons, more contrast
  • Essentially, post-patient collimation works like
    a grid.

57
Detector Sensitivity
  • The more sensitive the detector the more
    variation in photon energy it will resolve

58
Reconstruction Algorithm
  • Smooth algorithms improve contrast resolution
  • A rule of thumb
  • Increase spatial resolution decrease contrast
    resolution

59
Grayscale Manipulation
60
Distortion
61
Noise
62
Spatial Resolution
63
Post-Processing
  • Image Reformation
  • Image smoothing
  • Edge enhancement
  • Grayscale manipulation

64
Radiation Dose
  • Technical factor selection
  • Adjustments for children
  • Scanner dosimetry survey
  • Reducing scatter to the technologist

65
Data Acquisition
  • In CT data is acquired from either scintillation
    or gas-filled detectors.

66
Scintillation or Solid-state detectors
  • Various materials are coupled to photodiodes to
    record photon activity.
  • Examples of materials include
  • Cadmium tungstate
  • Ceramics doped with gadolinium or yttrium

67
(No Transcript)
68
Indirect Digital Radiography
  • The intensifying screen is made up of
    cesium-iodide crystals and the photodetector is
    made up of amorphous silicon.

69
(No Transcript)
70
(No Transcript)
71
(No Transcript)
72
(No Transcript)
73
(No Transcript)
74
(No Transcript)
75
(No Transcript)
76
(No Transcript)
77
(No Transcript)
78
(No Transcript)
79
(No Transcript)
80
(No Transcript)
81
(No Transcript)
82
Another Positive in the CT Debate
  • During the past several years there has been an
    ongoing discussion about how do we get people
    interested in being faculty.
  • Adding CT brings another group of potential
    faculty members to the table.
  • Certainly, we increase the probability of adjunct
    faculty to teach the CT component.
  • Also, we increase the exposure of our students to
    potential employers.

83
http//w4.siemens.de/FuI/en/archiv/zeitschrift/hef
t1_97/artikel03/index.html
84
(No Transcript)
85
(No Transcript)
86
http//www.impactscan.org/rsna2001.htm
87
(No Transcript)
88
Contrast Media
89
Photon Tissue Interactions
  • PE
  • CE

90
Scatter Control
91
Filtration
  • Compensating
  • Required
  • Effects on beam energy

92
Anode Heel Effect
  • Line focus principle

93
Exposure Creep
  • Look for article about pediatric overexposure in
    CT

94
Sensitivity of Image Receptor
  • Differences providing the ability to visualize
    different structures

95
Quantum Mottle
  • Along for fluoroscopy an excellent modality to
    demonstrate the effects of it.
  • Now possible with CR/DR

96
Cross-sectional anatomy
  • Provides further review for students
  • Allows them to learn about something they
    frequently see in the department and hospital.
  • Certainly helps with positioning and pathology
    review.

97
Equipment
  • Detectors
  • Tubes
  • FSS
  • Filtration
  • Collimation

98
Concepts
  • Spatial resolution
  • Contrast resolution
  • Image matrix
  • FoV

99
Patient Care
  • Contrast Media
  • Patient prep
  • Reactions
  • Dose rates
  • Venipuncture
  • Ionic v. non-ionic
  • Atomic number
  • Concentration
  • Barium versus iodine

100
Tubes
  • Anode heel effect
  • Line focus principle

101
Collimation
  • Total
  • Compensating
  • Pre and post
  • grid and patient dose

102
Tissue Interactions
  • Photoelectric effect
  • Absorption
  • Compton effect
  • Scatter
  • Attenuation

103
PE
  • Absorption
  • High contrast
  • Plain film radiography

104
CE
  • Low contrast
  • Scatter
  • High energy photons
  • More likely forward scatter
  • High energy photons
  • Less absorption (charts/graphs here)

105
Contrast resolution
  • This will be new
  • Gray scale
  • Dynamic range
  • High and low contrast
  • Count anatomical structures

106
Radiation Protection
  • Dose versus Image Quality

107
Quantum Mottle
  • Easily demonstrated
  • CR/DR applicable
  • Particularly when using appropriate techniques
  • Fluoroscopy applicable

108
Technique selection
  • No penalty for overexposure
  • Similar to CR/DR
  • Too little exposure is trouble
  • Quantum mottle
  • Exposure creep

109
Anatomy and Pathology
  • Opportunity to review diseases again

110
Spine
  • CSP
  • LSP
  • Intervertebral foramen
  • Zygo joints
  • Myelograms
  • Discograms
  • In some facilities this may be the only
    opportunity to see these exams

111
Stomach
  • Location
  • Position
  • Structures
  • Pathology
  • contrast

112
Kidney
  • Mention in last years student bowl
  • Position and angulation

113
Colon
  • Flexures and their position
  • Pathology
  • Appendicitis

114
Skull
  • Skull types
  • Angles
  • Visibility of structures

115
Extremities
  • Positional relationships between structures
  • Angles
  • Non-linear reconstructions

116
Patient Prep
  • Contrast
  • Instructions
  • Post-procedural care
  • Biopsies
  • Myelograms
  • Etc.

117
Review of Lab Values
  • Vital Signs
  • Hemoglobin
  • RBC
  • Platelets
  • O2
  • Prothrombin
  • Partial thromboplastin time

118
Several labs will only be done in CT
119
Consents
120
Postural hypotension
121
(No Transcript)
About PowerShow.com