VaNTH ERC Medical Imaging Taxonomy3/25/2002

Meredith GrowCynthia B. Paschal, PhD.

Note: Modules are being developed to include the concepts highlighted below.

I. Global conceptsA. Imaging/anatomic planes

1. Sagittal2. Coronal3. Transverse / transaxial / axial

B. Projections vs. tomographs – Part of avocado challengeC. Dimensions of images

1. Points (1D)2. Pixels (2D)3. Voxels (3D)

D. Noise ratios1. Signal to noise ratio2. (Change in signal) to noise ratio3. Contrast to noise ratio

E. Field of view, field of imageF. Image processing (intentionally abbreviated)

1. Filtering2. Segmentation3. Registration

II. X-ray based imagingA. Radiography (e.g. skeletal, chest, dental, mammography)

1. History of x-rays and x-ray imaginga. Roentgen's discovery - Part of Roentgen hand

challengeb. First diagnostic use; sewing needle in hand

2. X-ray generationa. X-ray as E-M radiation

i. X-rays related to E-M spectrumii. Wave concept of E-M radiation

iii. Particle concept of E-M radiationb. X-ray tube design and use

i. Target materialii. Tube design

1. Glass enclosure2. Anode3. Cathode4. Filament

iii. Focal spot sizeiv. kVp, mAsv. Filters

1. Inherent filtration2. Added filtration

a. Filter thicknessb. Effect on exposure factorsc. Wedge filtersd. Heavy metal filters;

Molybdenumc. Beam restrictors

i. Aperture diaphragms – Visible light x-ray simulation module

ii. Collimatorsd. Monochromatic beams

i. X-ray tube and crystalii. Synchrotron radiation

iii. Inverse Compton scattering3. X-ray propagation and interaction within target

a. Interactionsi. Coherent scattering

ii. Photoelectric effect1. Characteristic radiation2. Auger effect

iii. Compton scatteringiv. Pair production and photodisintegration

b. Attenuationi. Attenuation coefficients

ii. Density, atomic number, electrons per gram1. Effect on attenuation2. Relationship between the three

iii. Energy dependencyiv. Beam hardening

c. Probability (cross-section) vs. photon energy of different interactions for various biological materials (or approximations thereof, e.g. water)

d. Exposure and dose terminology and quantification4. X-ray detection and image formation

a. Conversion of x-ray photons to detectable signali. Oxidation of silver

ii. Fluorescence of a screeniii. Computed radiography

b. Gridsi. Terminology

1. Grid ratio2. Grid pattern

a. Linear gridb. Crossed gridc. Focused grid

d. Parallel gridii. Evaluation methods of grid performance

1. Primary transmission2. Bucky factor3. Contrast improvement factor

iii. Grid selectionc. Film

i. Emulsion and baseii. Latitude

iii. Optical densityiv. Relative exposure

d. Cassette construction (double emulsion)i. Cassette wall

ii. Protective coatingiii. Screen substrateiv. Reflective layer (to light)v. Phosphor

vi. Light sensitive emulsionvii. Film substrate

viii. Foam pad backinge. Image intensifiers

i. Construction1. Base2. Reflective coat3. Phosphor layer4. Protective layer

ii. Phosphor1. Intensifying action of screens2. Speed of calcium tungstate intensifying

screensiii. Electrical componentsiv. Efficiency

f. Compound radiography platesi. Materials

ii. Laser readoutg. Direct digital readout systems; e.g. amorphous siliconh. Artifacts

i. Penumbra; geometric unsharpness – Visible light x-ray simulation module

ii. Magnification – Visible light x-ray simulation module

iii. Blur – Visible light x-ray simulation moduleiv. Under- and over-exposurev. Scatter – Visible light x-ray simulation module

5. Applications and techniques

a. See X-ray instrumentation folder for images of x-ray hardware

b. Common applicationsi. Skeletal

ii. Chestiii. Portableiv. Dentalv. Mammography

c. Techniquesi. Tube type

ii. Parametersiii. Detectoriv. Effect of target on techniques (e.g. patient size)

d. Positioning issuese. Safety

i. History1. http://www.uihealthcare.com/depts/

medmuseum/trailoflight/03xraymartyrs.html

ii. Current practices1. Time2. Distance3. Shielding

a. Leaded glassb. Lead aprons

6. Image featuresa. General appearance of x-ray images (see X-ray image

folder) – Roentgen hand challengeb. Relative contrastc. Spatial and contrast resolutiond. Diagnostic information available in x-ray images (see

X-ray image folder)i. Anatomic

ii. Physiologiciii. Pathologic

B. Fluoroscopy1. History

a. Original viewing methodsb. Problems (e.g. dim light)

2. X-ray generation (see II.2)3. X-ray propagation and interaction within target (see II.3)4. X-ray detection and image formation

a. Fluorescent screeni. X-ray interaction

ii. Lack of output intensityb. Image intensifier

i. Design1. Input phosphor and photocathode2. Electrostatic focusing lens3. Acceleration anode4. Output phosphor

ii. Brightness gain1. Minification gain2. Flux gain

c. Viewing and recording the imagei. Direct viewing

ii. Optical system and cameras1. Lens2. Aperture3. Image distributor

a. Collimator lensb. Mirrorsc. Vignetting

4. Cameraa. Image size and framingb. Film exposure

iii. Closed-circuit television1. Vidicon camera2. Video signal3. Charge-coupled device TV camera4. Television monitor

iv. Television scanning1. Video signal frequency (bandpass)2. Synchronization

v. Television image quality1. Resolution2. Automatic brightness control

vi. Automatic gain control1. kVp variability2. mA variability3. Combined control4. Pulse width variability

vii. Fluoroscopic image recorders1. Light image recorders (spot film

recorders)2. Spot film cameras

a. Framing with spot film camerab. Exact framingc. Equal area framingd. Total framing

3. Cinefluorographya. Cine camera

b. Framingc. X-ray exposured. Synchronization

viii. TV image recorders1. Tape recorders2. Magnetic disc recorders3. Optical discs (CDs)

5. Applications and techniquesa. See Fluoroscopy instrumentation folder for images of

fluoroscopy hardwareb. Contrast agents

i. Ionicii. Non-ionic

iii. Injectediv. Ingested

c. Common applications and representative hardwarei. GI

ii. Orthopedicsiii. Angiography (cardiocath)

d. Techniquese. Positioning issuesf. Safety

i. Prolonged radiation exposure compared to plain film x-ray

ii. Timeiii. Distanceiv. Shielding

1. Leaded glass2. Lead apron

6. Image featuresa. General appearance of fluoroscopic x-ray images (see

Fluoroscopy image folder)i. Contrast

ii. Differences compared to plain film x-ray – Roentgen hand challenge

b. Artifactsi. Lag

ii. Bluriii. Noiseiv. Distortionv. Vignetting

c. Diagnostic information available in fluoroscopic x-ray images (see Fluoroscopy image folder)i. Anatomic

ii. Physiologiciii. Pathologic

C. CT1. History

a. Godfrey N. Hounsfieldb. Allan M. Cormack

2. X-ray generation (see II.2)3. X-ray propagation and interaction within target (see II.3)4. X-ray detection and image formation

a. Detectorsi. Function

ii. Construction1. Scintillation crystals2. Xenon gas ionization chambers3. Photomultiplier tubes

iii. Sensitivityiv. Efficiencyv. Detector configurations

1. First generation (translate-rotate, one detector)

2. Second generation (translate-rotate, multiple detectors)

3. Third generation (rotate-rotate)4. Fourth generation (rotate-fixed)5. Other modes

a. Multiple tubesb. Electron beam CT

b. Computeri. Control

ii. Processingiii. Storage and retrieval

c. Display unit and camerad. Image reconstruction

i. Image components1. Pixel2. Voxel

ii. Sinogramiii. Algorithms for image reconstruction

1. Back projection2. Iterative methods

a. Simultaneous reconstructionb. Ray-by-ray correctionc. Point-by-point correction

3. Analytic methodsa. Two-dimensional Fourier

analysisb. Filtered back-projections

iv. CT numbers, Hounsfield units

v. Image display5. Application and techniques

a. See CT instrumentation folder for images of CT hardware

b. Applicationsi. Neurological

ii. Skeletaliii. Soft tissueiv. Vascular (electron beam)v. Cardiac (electron beam)

c. Techniquesi. Slices vs. 3-D volume rendering

ii. Contrast agents1. Ionic2. Non-ionic

iii. Dosingd. Positioning issuese. Safety

i. Timeii. Distance

iii. Shieldingiv. Scatter

6. Image featuresa. General appearance of CT images (see CT image

folder)b. Noise

i. Effect on visibilityii. Sources

iii. Factors affection noise1. Pixel size2. Slice thickness3. Radiation exposure

iv. Window settingv. Filtration

c. Artifactsi. Motion artifacts

ii. Streak artifactsiii. Beam-hardening artifactsiv. Ring artifactsv. Centering

vi. Partial volume effectd. Diagnostic information available in CT images (see CT

image folder)i. Anatomic

ii. Physiologiciii. Pathologic

III. Nuclear imagingA. History

1. 1954 – Photorecording radionuclide scanner; David E. Kuhl2. 1964 – Mark II emission tomographic scanner; Kuhl &

Edwards3. Kuhl goes on to develop techniques of SPECT and principles

of PET4. 1976 – First fluorodeoxyglucose PET image obtained at the

Hospital of the University of Pennsylvania (HUP)5. 1981 – Coincident system based scintillation camera detectors

developed at HUP6. http://www.rad.upenn.edu/Depart/highlights.html

B. Radionuclides: sources and tracers1. Nuclear particles

a. Betab. Gammac. Positron

2. Physical properties of radionuclidesa. Physical half-lifeb. Specific activity

3. Nuclear sourcesa. Nuclear reactorsb. Charged-particle acceleratorsc. Photonuclear activation

4. Tracer typesa. Photon-emitting radionuclides

i. 99mTc1. Macroaggregated albumin2. Sulfur collois3. Sestimbi4. Pertechnetate5. Methylene diphosphate

ii. Molybdenum 99iii. Iodine 123 & 131iv. Xenon 133v. Gallium 67

vi. Indium 111 & 113mvii. Thallium 201

viii. Krypton 81mb. Positron-emitting radionuclides

i. Carbon 11ii. Nitrogen 13

iii. Oxygen 15iv. Fluorine 18 (e.g. - fluorodeoxyglucose)v. Gallium 68

vi. Rubidium 82

5. Unitsa. Curieb. Becquerel

C. Interaction of tracer with target1. Interaction of nuclear particles and matter

a. Beta particlesb. Gamma raysc. Positron

2. Radionuclide biological propertiesa. Biological half-lifeb. Clearance mechanismsc. Differential uptake (biodistribution)d. Toxicity

3. Attenuation of photons4. Positron annihilation5. Units

a. grayb. Dose equivalent (rem)c. radd. Quality factor (QF)

D. Photon detection and image formation1. Nuclear radiation detectors

a. Ion collection detectorsb. Scintillation detectorsc. Solid-state detectors

2. Radionuclide imaging scannersa. Rectilinear scannerb. Gamma/scintillation camera

i. Camera characteristics1. Sensitivity2. Field of view

ii. Collimators1. Parallel-hole collimators2. Diverging collimators3. Converging collimators4. Pin-hole collimators

iii. Crystalsiv. Photomultiplier tube arrayv. Image formation

1. Iterative reconstruction2. Attenuation correction3. Scatter correction

vi. Spectrometry1. Gamma spectrum2. Statistical fluctuations3. Compton scatter

4. Characteristic x-rays5. Background6. Composite spectrum

vii. Pulse height analyzerviii. Specialized gamma cameras

1. Geiger-Mueller counter2. Ionization chamber

c. Back projectionE. Applications and techniques

1. See Nuclear medicine instrumentation folder for images of nuclear medicine hardware

2. Radionuclide imaging methodsa. Longitudinal section tomographyb. Single-photon emission computed tomography

(SPECT)i. Instrumentation

ii. Data acquisition1. Attenuation correction2. Acquisition time3. Image matrix size4. Number of views

iii. Tomographic image production1. Image filtering2. Image display

c. Positron emission tomography (PET)d. Integrated imaging systems (e.g. CT/SPECT)

3. Diagnostic applicationsa. Gamma camera

i. Cerebrovascularii. Cardiovascular

iii. Respiratoryiv. Gastrointestinalv. Skeletal

vi. Genitourinaryvii. Neoplasm imaging

viii. Inflammation and infectionb. SPECT

i. Cerebrovascularii. Cardiovascular

iii. Gastrointestinalc. PET

i. Cerebrovascularii. Cardiovascular

iii. Neoplasm imaging (oncology)4. Safety

a. Occupational dose limits

i. Total effective dose equivalentii. Deep dose equivalent

iii. Committed dose equivalentiv. Shallow dose equivalent whole body/maximal

extremityv. Lens dose equivalent

b. Critical organ dosesRadiopharmaceutical Procedure Critical organ Critical organ

dose99mTc pertechnetate brain scan intestine 1.3 mGy/mCi99mTc pertechnetate thyroid scan intestine 2.5 mGy/mCi99mTc microspheres lung scan lung 2.1 mGy/mCi

131I hippuric acid kidney scan bladder 100.0 mGy/mCiF. Image features

1. General image appearance2. Image quality

a. Image contrastb. Spatial resolutionc. Blur and visibility of detail

i. Motionii. Gamma camera blur

d. Image noisee. Uniformityf. Spatial Distortion

3. Diagnostic information available a. Anatomicb. Physiologicc. Pathologic

IV. UltrasoundA. History

1. 1877 – Lord Rayleigh's treatise "The theory of Sound" delineates fundamental physics of sound vibrations/waves

2. 1880 – Piezoelectric effect discovered by Pierre and Jacques Curie

3. 1914 – Reginald A. Fessenden designs and builds first working sonar system

4. 1941 – Floyd A. Firestone produced patented "supersonic reflectoscope"

5. 1942 – Karl Theodore Dussik first physician to use ultrasound in medical diagnosis

6. 1953 – Hand-held B mode instrument used to visualize tumors in breast tissue, Wild and Reid

7. 1957 – Compound B-mode contact scanner, Brown and Donald8. Timeline extracted from _________

B. Sound waves *** ultrasound material highlighted is included in US online instructional module ***1. The wave equation2. Wave characteristics

a. Frequencyb. Velocity (see IV.C.1)

i. Compressibilityii. Density

c. Wavelengthd. Amplitudee. Intensity

3. Constructive and destructive interference4. Phase velocity5. Doppler effect6. Transducers

a. Characteristics of piezoelectric crystalsb. Curie temperaturec. Resonant frequencyd. Transducer Q factore. Types

i. Mechanical sector scanii. Linear arrays

iii. Phased arrays1. Transmit steering2. Receive steering3. Transmit focus

f. Designi. Matching layer

ii. Piezoelectric elementiii. Backing layeriv. Housingv. Electrodes

C. Wave propagation and interaction with target1. Properties of media

a. Densityb. Speed of soundc. Impedanced. Temperature dependence

2. Propagationa. Stress and strain relationshipb. Transverse, shear and longitudinal waves

3. Target interaction

a. Reflectionb. Transmissionc. Refractiond. Scattere. Absorptionf. Attenuation

D. Wave detection and image formation1. Transducers

a. Characteristics of piezoelectric crystalsb. Curie temperaturec. Resonant frequencyd. Transducer Q factore. Types

i. Mechanical sector scanii. Linear arrays

iii. Phased arrays1. Transmit steering2. Receive steering3. Transmit focus

f. Designi. Matching layer

ii. Piezoelectric elementiii. Backing layeriv. Housingv. Electrodes

2. Display methodsa. A mode ultrasoundb. T-M mode ultrasoundc. B mode ultrasound

i. Receive focus (dynamic focus)ii. Doppler imaging

iii. Parallel systemsiv. Harmonic imaging

d. C mode ultrasound3. Display controls

a. Time gain compensatorb. Delayc. Intensityd. Coarse graine. Rejectf. Near gaing. Far gainh. Enhancement

E. Applications and techniques1. See Ultrasound instrumentation folder for images of

Ultrasound hardware

2. Applicationsa. Obstetricsb. Cardiacc. Ophthalmologicd. Vasculare. Trans-rectal prostatef. Trans-vaginal (OB and cervical)g. Inter-luminalh. Intra-operative

3. Techniquesa. Transducer selectionb. Mode selectionc. Parameter selectiond. Continuous Dopplere. Pulsed Dopplerf. Doppler color flow imagingg. Contrast agents

4. Positioning issuesa. Position of transducer relative to organ of interestb. Change of patient position for diagnosis (i.e. – gall

stone movement as opposed to stationary growth)c. Acoustic window

5. Safetya. Heat depositionb. Cavitation

F. Image features1. General appearance of ultrasound images2. Speckle3. Resolution

a. Depth (axial) resolutioni. Reverberation echoes

b. Lateral (horizontal, or azimuth) resolutioni. Focused transducers

ii. Tomographic thicknessc. Spatial resolutiond. Contrast resolutione. Temporal resolution

4. Noise5. Artifacts

a. Shadowingb. Enhancementc. Reverberation

6. Sources of noise and artifactsa. Side lobesb. Grating lobes

c. Transducer element crosstalk (mechanical and electrical)

d. System electrical noise7. Sources of distortion

a. Speed of sound variationb. Rasterization

8. Diagnostic information available in ultrasound imagesa. Anatomicb. Physiologicc. Pathologic

V. MRIA. History

1. Rabi et al – resonant atomic beam, nuclear magnetism (1938)2. Bloch, Hansen & Packard; Purcell, Torrey & Pound –

liquid/solid NMR; resonant coils (1946)3. Damadian – MRI (1971)4. Lauterber; Mansfield – MRI (1973)5. Commercial scanners (1981)6. Echo planar scanners (~1989)

B. Resonance, excitation and relaxation1. E-M fields

a. Main magnetic field; Bob. Magnetic moment; (mu)c. Applied radio-frequency field; B1

2. Nuclear angular momentum3. Magnetism and the magnetic dipole moment

a. Magnetic field due to electron flowb. Magnetic dipole moment

i. Magnetic dipole moments for rotating chargesii. Magnetic dipole moments for nuclei

c. Angular momentum and precessiond. Larmor frequencye. Chemical shiftf. Energy states for nuclear spin systemsg. Boltzman distributionh. Magnetization vector

4. Excitationa. On/off resonanceb. Direct excitationc. Magnetization transferd. Selectivee. Non-selective

5. Relaxationa. Spin-lattice (longitudinal) relaxation

i. Time constant (T1)ii. Factors affecting spin-lattice relaxation

b. Spin-spin (transverse) relaxationi. Free induction decay

ii. Time constant (T2)iii. Factors affecting spin-spin relaxationiv. T2*

C. Imaging mechanics1. Magnetic field gradient coils

a. Slice selectionb. Phase encodingc. Frequency encoding

2. Radio-frequency coilsa. Planarb. Bird-cagec. Helmholtzd. Phased array

3. Pulse sequencesa. Stimulated echoesb. Spin echo

i. Single echoii. Multi-echo

iii. Fast spin echoc. Gradient echo

i. Spoiledii. Unspoiled

iii. Steady stateiv. Non-steady state

d. Inversion recoveryi. Inverting RF pulse

ii. Inversion time (TI)iii. Forming the signaliv. Short TI inversion recovery (STIR)

4. Repetition time (TR)5. Echo time (TE)6. Flip angle7. k-space trajectory

a. Single-shotb. Multi-shotc. Segmented k-spaced. Spiral

8. Shimminga. Staticb. Dynamic

9. Tuning10. Fat saturation

a. Chemical shift selectiveb. T1 selective

11. 2D & 3D imagingD. Signal detection and image formation

1. Receiver coils2. Demodulation3. k-space

a. Spatial frequencyb. Nyquist sampling

4. Filters5. Resampling/regridding of non-gridded data6. Fourier transform7. Back projection

E. Applications and techniques1. See MRI instrumentation folder for images of MRI hardware2. Common applications

a. Neurologicalb. Orthopedic/musculoskeletalc. Cardiovasculard. Vasculare. Thoraco-abdominalf. Pelvicg. Spectroscopyh. Interventional

3. functional MRI (fMRI)a. Blood oxygen level dependent (BOLD) imaging

i. Physiologic response to activationii. Deoxyhemoglobin and signal strength

b. Paradigm designi. Stimulus or task

ii. Controlc. Data processing

4. Techniquesa. T1 & T2 weighted imagesb. Flow sensitive methods

i. Phase velocity encoding (phase contrast)ii. Tagging

c. Multi-planar imagingd. Fast imaging methods

i. Reduced flip angleii. View sharing/keyhole

iii. Multishotiv. Spiralv. EPI

vi. View reductionvii. SMASH/SENSE

e. Cardiac triggeringi. Signals

1. ECG pulse plethysmography 2. O2 saturation3. Navigators

ii. Trigger delayiii. Prospective triggeringiv. Retrospective triggering

f. Respiratory compensationi. Signals

1. Respiratory bellows2. Navigators3. Thermisters4. Flow meters5. Etc.

ii. Gatingiii. ROPE, COPEiv. Breath holdv. Navigators

5. Positioning issues6. Safety

a. Human exposure considerationsi. Static and gradient magnetic fields

ii. Radio frequency fieldsiii. Specific absorption ratio (SAR)iv. dB/dtv. MRI during pregnancy

b. Magnetic field hazardsi. Projectile effects

ii. Effects on surgically implanted devicesiii. Metallic foreign bodiesiv. Life support devices

F. Image features1. General appearance of MR images2. Contrast

a. Proton densityb. T1 weightingc. T2 weightingd. Contrast to noise ratioe. Signal difference to noise ratio

3. Image noisea. Noise considerationsb. SNR considerations

i. Voxel sizeii. Field strength

iii. Tissue characteristicsiv. TR, TE, TI, flip anglev. RF coils

vi. Averaging, NEX, NSA4. Diagnostic information available in MR images

a. Anatomicb. Physiologicc. Pathologic

Works Cited

Chandra, Ramesh. Introductory Physics of Nuclear Medicine. Philadelphia: Lea &

Febiger, 1992.

Curry, Thomas S. et al. Christensen's Physics of Diagnostic Radiology 4 th Ed.

Philadelphia : Lea & Febiger, 1990.

Mettler, Fred A, and Milton J. Guiberteau. Essentials of Nuclear Medicine Imaging, 4 th

Ed. Philadelphia: W.B. Saunders Company, 1998.

Shung, K. Kirk et al. Principles of Medical Imaging. San Diego: Academic Press, Inc.

1992.

Sprawls Jr., Perry. Physical Principles of Medical Imaging. Rockville, MD: Aspen

Publishers Inc. 1987.

Special ThanksDr. Bob GallowayDr. Ron PriceRadiology Dept. VUMC2001 VaNTH REU students