medical imaging dr. hugh blanton entc 4390. dr. blanton entc 4390 --introduction 2 there has been an...
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MEDICAL IMAGING
Dr. Hugh Blanton
ENTC 4390
Dr. Blanton ENTC 4390 --Introduction 2
• There has been an alarming increase in the number of things I know nothing about!
Lecture 1
INTRODUCTION
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INTRODUCTION TO MEDICAL IMAGING INTRODUCTION TO MEDICAL IMAGING
• Medical imaging of the human body requires some form of energy. • In radiology, the energy used to produce the
image must be capable of penetrating tissues. • The electromagnetic spectrum outside the visible
light region is used for • x-ray imaging,• magnetic resonance imaging, and • nuclear medicine.
• Mechanical energy, in the form of high-frequency sound waves, is used in ultrasound imaging.
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INTRODUCTION TO MEDICAL IMAGING INTRODUCTION TO MEDICAL IMAGING
• With the exception of nuclear medicine, all medical imaging requires that the energy used to penetrate the body’s tissues also interact with those tissues. • Absorption,• Attenuation, and• Scattering.
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INTRODUCTION TO MEDICAL IMAGING INTRODUCTION TO MEDICAL IMAGING
• If energy were to pass through the body and not experience some type of interaction (e.g., absorption, attenuation, scattering), • then the detected energy would not
contain any useful information regarding the internal anatomy, and
• thus it would not be possible to construct an image of the anatomy using that information.
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INTRODUCTION TO MEDICAL IMAGING INTRODUCTION TO MEDICAL IMAGING
• In nuclear medicine imaging, radioactive agents are injected or ingested, and it is the metabolic or physiologic interactions of the agent that give rise to the information in the images.
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• The power levels used to make medical images require a balance between patient safety and image quality.
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History, Basic Principles, & ModalitiesHistory, Basic Principles, & Modalities
Class consists of:1) Deterministic Studies
- distortion- impulse response- transfer functions
All modalities are non-linear and space variant to some degree.
Approximations are made to yield a linear, space-invariant system.
2) Stochastic StudiesSNR (signal to noise ratio) of the resultant
image - mean and variance
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Nov. 1895 – Announces X-ray discovery
Jan. 13, 1896 – Images needle in patient’s hand
– X-ray used presurgically
1901 – Receives first Nobel Prize in Physics
– Given for discovery and use of X-rays.
Wilhelm Röntgen, WurtzburgWilhelm Röntgen, Wurtzburg
Radiograph of the hand of Röntgen’s wife, 1895.
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Röntgen’s SetupRöntgen’s Setup
Röntgen detected: • No reflection• No refraction• Unresponsive to mirrors or lenses
His conclusions:• X-rays are not an EM wave • Dominated by corpuscular behavior
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Projection X-RayProjection X-Ray
Disadvantage: Depth information lost Advantage: Cheap, simple
)z(f),,(μ densityelectron , zyx attenuation coefficient
Measures line integrals of attenuation )dlμ(od I I x,y,ze
Film shows intensity as a negative ( dark areas, high x-ray detection
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Sagittal Coronal
Body Structure
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Directional TermsDirectional Terms
• Anatomical position• Beginning reference point• Body upright• Facing front• Arms at side, palms forward• Feet parallel
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Directional TermsDirectional Terms
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Planes of DivisionPlanes of Division
• Frontal plane• Coronal plane• Divides body into anterior, posterior
parts
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Planes of DivisionPlanes of Division
• Sagittal plane• Divides body into right, left portions• If plane cuts midline, called midsagittal
or medial plane
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Planes of DivisionPlanes of Division
• Transverse plane• Divides body into superior, inferior parts
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Anatomical DirectionsAnatomical Directions
• Anterior (ventral) = toward front of body
• Posterior (dorsal) = toward back of body
• Medial = toward midline of body• Lateral = toward side of body• Proximal = nearer to reference point• Distal = farther from reference point
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Body CavitiesBody Cavities
• Dorsal cavity contains:• Cranial cavity• Spinal cavity
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Body Cavities (cont’d)Body Cavities (cont’d)
• Ventral cavity contains:• Thoracic cavity• Diaphragm
• Separates • thoracic cavity and • abdominal cavity
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Body Cavities (cont’d)Body Cavities (cont’d)
• Abdominopelvic cavity:• Abdominal cavity• Pelvic cavity• Peritoneum
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Body RegionsBody Regions
• Imaginarily divided into 9 regions
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Body RegionsBody Regions
• Midline sections:• Epigastric = above
stomach• Umbilical = umbilicus
or navel• Hypogastric = below
the stomach
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Body Regions (con’t)Body Regions (con’t)
• Lateral sections:• Right and left
hypochondriac• Positioned near
ribs, specifically cartilages
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Body Regions (con’t)Body Regions (con’t)
• Right and left lumbar• Positioned
near small of back (lumbar region)
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Body Regions (con’t)Body Regions (con’t)
• Right and left iliac• Named for
upper bone of hip (ilium)
• Also called inguinal region (referring to groin)
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Body PositionsBody Positions
• Anatomical• Standing erect, facing forward, arms at sides,
palms forward, toes pointed forward
• Prone• Lying face down
• Supine• Lying face up
X-Ray
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Early DevelopmentsEarly Developments
• Intensifying agents, contrast agents all developed within several years.
• Creativity of physicians resulted in significant improvements to imaging.
- found ways to selectively opacify regions of interest
- agents administered orally, intravenously, or via catheter
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Later DevelopmentsLater DevelopmentsMore recently, physicists and engineers have initiated new
developments in technology, rather than physicians.
1940’s, 1950’s
Background laid for ultrasound and nuclear medicine
1960’s
Revolution in imaging – ultrasound and nuclear medicine
1970’s
CT (Computerized Tomography)
- true 3D imaging
(instead of three dimensions crammed into two)
1980’s
MRI (Magnetic Resonance Imaging)
PET ( Positron Emission Tomography)
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1972 Hounsfield announces findings at British Institute of Radiology1979 Hounsfield, Cormack receive Nobel Prize in Medicine(CT images computed to actually display attenuation coefficient x,y
Important Precursors:1917 Radon: Characterized an image by its projections1961 Oldendorf: Rotated patient instead of gantry
Computerized Tomography (CT)Computerized Tomography (CT)
),(),(ID yxμyx Result:
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First Generation CT ScannerFirst Generation CT Scanner
Acquire a projection (X-ray)Translate x-ray pencil beam and detector across body and record output
Rotate to next angleRepeat translation
Assemble all the projections.
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Reconstruction from Back ProjectionReconstruction from Back Projection
1.Filter each projection to account for sampling data on polar grid 2. Smear back along the “line integrals” that were calculated by the detector.
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Modern CT Scanner Modern CT Scanner
From Webb, Physics of Medical Imaging
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Computerized Tomography (CT), continued
Computerized Tomography (CT), continued
Early CT Image Current technology
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Inhalation
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Exhalation
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Nuclear MedicineNuclear Medicine
a) Radioactive tracer is selectively taken up by organ of interest
b) Source is thus inside body!
c) This imaging system measures function (physiology)
rather than anatomy.
- Grew out of the nuclear reactor research of World War II- Discovery of medically useful radioactive isotopes1948 Ansell and Rotblat: Point by point imaging of thyroid1952 Anger: First electronic gamma camera
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Nuclear Medicine, continuedNuclear Medicine, continuedVery specific in imaging physiological function - metabolism
- thyroid function- lung ventilation: inhale agent
Advantage: Direct display of disease process.Disadvantage: Poor image quality (~ 1 cm resolution)
Why is resolution so poor?Very small concentrations of agent used for safety.
- source within bodyQuantum limited:
CT 109 photons/pixelNuclear ~100 photons/pixel
Tomographic systems: SPECT: single proton emission computerized tomography
PET: positron emission tomography
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Combined CT / PET Imaging
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Comparison of ModalitiesComparison of Modalities
Why do we need multiple modalities?Each modality measures the interaction between energy and biological tissue.
- Provides a measurement of physical properties of tissue.- Tissues similar in two physical properties may differ in a
third.
Note: - Each modality must relate the physical property it measures
to normal or abnormal tissue function if possible.- However, anatomical information and knowledge of a large
patient base may be enough. - i.e. A shadow on lung or chest X-rays is likely not
good. Other considerations for multiple modalities include:
- cost - safety - portability/availability
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Measures attenuation coefficient
Safety: Uses ionizing radiation - risk is small, however, concern still
present. - 2-3 individual lesions per 106
- population risk > individual risk i.e. If exam indicated, it is in your interest
to get exam
Use: Principal imaging modalityUsed throughout body
Distortion: X-Ray transmission is not distorted.
),,(μ zyx
X-RayX-Ray
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UltrasoundUltrasound
Measures acoustic reflectivity
Safety: Appears completely safe
Use: Used where there is a complete soft tissue and/or fluid path
Severe distortions at air or bone interface
Distortion: Reflection: Variations in c (speed) affect depth estimateDiffraction: λ ≈ desired resolution (~.5 mm)
),,R( zyx
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Magnetic Resonance (MR)Magnetic Resonance (MR)
Multiparametric M(x,y,z) proportional to ρ(x,y,z) and T1, T2. (the relaxation time constants) Velocity sensitive
Safety: Appears safe Static field - No problems
- Some induced phosphenes Higher levels - Nerve stimulation
RF heating: body temperature rise < 1˚C - guideline
Use:
Distortion: Some RF penetration effects - intensity distortion
T/s 10dt
dB
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Chest Abdomen Head
X-Ray/
CT
+ widely used
+ CT - excellent
– needs contrast
+ CT - excellent
+ X-ray - is good
for bone
– CT - bleeding,
trauma
Ultrasound – no, except for
+ heart
+ excellent
– problems with
gas
– poor
Nuclear + extensive use
in heart
Merge w/ CT + PET
MR + growing
cardiac
applications
+ minor role + standard
Clinical Applications - TableClinical Applications - Table
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Cardiovascular Skeletal / Muscular
X-Ray/
CT
+ X-ray – Excellent, with
catheter-injected
contrast
+ strong for skeletal system
Ultrasound + real-time
+ non-invasive
+ cheap
– but, poorer images
– not used
Nuclear + functional information
on perfusion
+ functional - bone marrow
MR + getting better
High resolution
Myocardium viability
+ excellent
Clinical Applications - TableClinical Applications - Table
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Economics of modalities:Economics of modalities:
X-Ray: CheapestUltrasound: ~ $100K – $250K CT: $400K – $1.5 million (helical scanner)MR: $350K (knee) - $4.0 million Service: Annual costs
Hospital must keep uptimeStaff: Scans performed by technologistsHospital Income: Competitive issues Significant investment and
return