ct ch 11-14 (skipping 13)

• (found in 3rd gen ct)
• allows xray tube & detectors to rotate continuously so that a volume of the pt (rather than one slice) can be scanned very quickly in a single breath hold

• distance between turns and fastener
• distances in mm that the ct table moves during one revolution of xray tube

distance table travels during 360 deg revolution divided by slice thickness (or beam collimation)

slice thickness or beam collimation

image quality & pt dose

• pitch x slice thickness
• (beam cvollimation x scan time)

the slice thickness & in most cases equals the table increments (pitch of 1)

smaller structures require smaller/narrower collimation (whereas  larger structures require wider collimation)

table speed

pitch increases (decrease or loss of image detail)

• when using same parameters no change
• however in some studies showed SSCT better at imaging smaller objects

beam intensity, beam quality, slice thickness & matrix size & interpolation algorithms

less

more (degrades image quality)

about equal

reduces

volume coverage & speed can be increases by using a higher pitch, but image quality is degraded

• multisection
• multidetector
• multichannel

• radiation sensor
• suitable electronic device

1972

1998

improve volume coverage speed performance of both single & dual slice ct scanners

slice thickness & affects volume coverage speed performance

a thin collimation results in better resolution but takes longer to scan

fan beam

pitch and width of precollimator

slice thickness

becomes wider to cover the 2D detector array

cone beam

more scatter radiation in all directions

distance the table travels per rotation divided by the total collimation

increases

reduced

because could potentionally be missing slices

4-320

distance between 2 points used for interpolation

smaller the Z-gap, better the image quality

same as SSCT-distance between 2 points used for interpolation (can increase overlap between helices)

however determined by pitch & detector row spacing

better quality images

spiral/helical scanning, longitudinal interpolation & fan beam reconstruction

larger, artifacts become more pronounced

-increases dose

Exact & Approximate

• a cone beam algorithm (MSCT)
• not successful
• computionally complex & difficult to implement

• a cone beam algorithm (MSCT)
• 3D-feldkamp-Davis-Kress (FDK)
• 2D-advanced single slice rebinning (ASSR)

• 1. uniform
• 2. nonuniform
• 3. hybrid

(MSCT)

matrix detector, or fixed-array or linear array detector

(MSCT)

variable, adaptive-array detectors

• (type of MSCT detector)
• aka uniform, fixed array or linear array detector

• type of MSCT detector
• aka non uniform, adaptive-array detector

• Gas ionization detectors
• Solid-State detectors

• have low quantom detection efficiency and they have low xray absorption 
• used in SSCT, not MSCT

• scintilation crystal  or ceramics
• rare earth crystals, cadmium tungstate

detectors are doped with dopants (ex europium) to decrease the afterglow below 0.1% at 100ms

detector technology

• SSCT=gas ionization detector
• MSCT=solid state detector

a term that describes the number of data collection channels & the effective section of thickness determined by the data acquisition system settings

• preprocessing
• image reconstruction
• post processing

• size of voxel used in volume data set 
• when the slice thickness is equal to pixel size, all dimensions of the voxel are equal-or a perfect cube

• ability of scanner to improve fine detail
• measured in lp/cm or lp/mm

ability of the scanner to differentiate small differences in tissue contrast

• increase in speed & volume coverage
• improved spatial resolution
• efficient use of xray beam
• potential to reduce radiation exposure
• cardiac ct imaging

headache, slurred speech, confusion, facial droop, tremors, vomiting, & tetany

• normal brain tissue appears as shades of gray
• ventricles appear dark
• portions that are dark are areas lacking blood supply due to stroke

areas of dense white indicate a hemorrhage (bleed)

• RLQ pain
• vomiting 
• cramping
• fever
• abdominal pressure

• chest pain
• back pain
• arm pain
• shortness of breath
• high D-dimer

• abdominal aortic aneurysm
• back pain
• flank pain
• weakness
• pallor
• ashen skin tone if ruptured
• & abdominal pressure

• same as AAA
• usually very painful
• back pain
• & painful to move in any way

• streaks
• shading
• rings & bands

• an artifact
• intense straight lines across an image

• improper sampling
• partial volume averaging
• motion
• metal
• beam hardening
• noise
• spiral/helical scanning
• mechanical failure

• an artifact
• produced when the projection readings of a single channel or a group of channels consistently deviate from the truth

defective detector cells, deficiencies in system calibration or from suboptimal image-gen scanner

3rd generation

• an artifact
• near an object of high densities

• beam hardening
• partial volume averaging
• spiral/helical scanning
• scatter
• off-focal radiation
• incomplete projection

• voluntary-breathing, swallowing
• involuntary-head motion with injury, peristalsis, cardiac motion

purpose of 3D imaging is to use the vast amounts of data collected from the patient by volume ct scaning to provide both qualitative & quantitative info in a wide range of clinical applications

• type of rationale
• used to compare how observers perform on a specific vast to demonstrate the diagnostic value of 3D imaging

• type of rationale
• used to assess three elements of the technique: precision, accuracy & efficiency of 3D imaging procedure

• xyz
• aka-Cartesian System

multidimensional image; rectangular array of voxels with assigned values

Anatomical region represented by the scene

values assigned to the voxels in a scene

length of a side of the square cross-section of a voxel

origin & orthogonal axes system affixed to the imaging device

origin & orthogonal axes system affixed to the scene

origin & orthogonal axes system affixed to the object or object system

2D image depicting the object info captured in a scene or object system

translate, rotate, or scale scenes, objects or surfaces

extract structural information about the object from the 3Dspace

take measurements from the image's view space on the computer screen

view the 2D screen of the computer monitor

• generation of a 3D object using computer software
• Uses mathematics to describe physical properties of an object
• used to transform a 2D profile into a 3D object

• several shading algorithms
• Shading determines the final appearance of surfaces of the 3D object
• Lighting helps us to see the shape & texture of the object

• final step in process of generating a 3D object
• a computer program that converts the anatomical data collected from the patient into the 3D image seen on the computer screen

Surface & Volume

• type of 3D rendering
• uses only the surface contour data

• type of 3D rendering
• uses the entire data set

• simplest method of 3D imaging
• Like MPR (sag, coronal, paraaxial)
• it is a 2D image displayed on a flat screen

• Most popular 3D imaging approaph
• Techniques for extracting multidimensional info from the given image data & for depicting such info in the 2D view space by a process of projection
• (surface & volume redering)

2D

• produces a true 3D visualization mode
• Must not be confused with volume rendering

• Input-refers to device that acquired data
• Workstation-a powerful computer that can hand 3D imaging operations
• Output-displays the results
• User

process that starts with a stack of sectional slices collected by some medical imaging device and results in computer synthesized displays that facilitate the visulazation of underlying spatial relationships

• 1. data acquisition
• 2. creation of 3D space or scene space
• 3. processing for 3D image display
• 4. 3D image display

• aka surface display
• computer creates an internal representation of surfaces that will be visible in the displayed image...it then lights them according to a standard protocol &  displays the image according to its calculation of how the light rays would be reflected to viewers eye

• surface formation
• depiction on a computer screen

• much less storage space
• (but not as much info as volume rendering)

• 3D images have better image quality & provide more info compared with SR techniques
• Uses the entire data set
• & requires more computer power

• Preprocessing 
• Rendering

• used in 3D imaging
• extension of MPR techniques
• consist of generating arbitrary thick slices from thin slices, reducing the noise level and possibly improving the visualization of structures

• average intensity projection
• maximum intensity projection
• minimum intensity projection

• type of Intensity projection rendering used in 3D CT
• algorithm intended to create a thick MPR image by using the average of the attenuation through the tissues of interest to calculate the pixel viewd on the computer

• type of Intensity projection rendering used in 3D ct
• Volume Rendering technique
• Algorithm where only tissues with greatest attenuation will be displayed for viewing by observer

• Maximum intensity projection
• vessels containing contrast are clearly seen

• type of Intensity Projection Rendering used in 3D CT
• ensures only the tissues with the minimum or lowest attenuation will be displayed for viewing by the observer
• Least used projection

provides a valuable perspective in defining lesions for surgical planning or detecting subtle small airway diseases