introduction to anatomical imaging techniques october 7,...
TRANSCRIPT
Introduction toAnatomical Imaging
Techniques
October 7, 2014
Introduction toAnatomical Imaging
Techniques
October 7, 2014
Introduction to AnatomicImaging Methods
Survey of different methods of imaginghuman anatomy
RadiographyFluoroscopyComputed Tomography (CT)Ultrasound (US)Magnetic Resonance Imaging (MRI)
Provide background to enable studentsto identify and understand imagespresented in later lectures
(Not a presentation of imaging physics -This comes from other BMP courses &labs)
Introduction to AnatomicImaging Methods
Survey of different methods of imaginghuman anatomy
RadiographyFluoroscopyComputed Tomography (CT)Ultrasound (US)Magnetic Resonance Imaging (MRI)
Provide background to enable studentsto identify and understand imagespresented in later lectures
(Not a presentation of imaging physics -This comes from other BMP courses &labs)
Assignments(10/7/2014)
• http://www.nlm.nih.gov/research/visible/visible_human.html– Explore -- do not memorize
http://www.nlm.nih.gov/research/visible/visible_human.html
http://www.nlm.nih.gov/research/visible/visible_human.html
“Squire’s Fundamentals of Radiology” byRobert A. Novelline
(intended for medical student radiologycourse)
Radiography
Roentgen - 1895 - Discovery & almostimmediate applications exploringmedical use of x-rays
First Nobel Prize in Physics awarded toRoentgen in 1901
x-rays- short wavelength electromagneticradiation
Many objects that are opaque toordinary light are penetrated by x-rays
Causes fluorescence in certain“detector” materials. (Visible light isemitted from the detector material whenx-rays strike it)
radiopaquex-rays are absorbed bydenser materials - metals & minerals
radiolucentx-rays pass throughless dense materials
radiopaquex-rays are absorbed bydenser materials - metals & minerals
radiolucentx-rays pass throughless dense materials
Fluoroscopic ViewRadiographic View
Fluoroscopic imagingradiopaque areas appear darkweak light intensity
Photographic film radiographyfilm optimized for visible light
radiopaque areas appear bright“negative” photography
Call them “Radiographs” not “x-rays”
Radiographs are “shadowgrams”Thickness and composition areimportant
Objectives far from the detector are“magnified”
Anatomy of interest should be asclose to the detector as possible
Fluoroscopic imagingradiopaque areas appear darkweak light intensity
Photographic film radiographyfilm optimized for visible light
radiopaque areas appear bright“negative” photography
Call them “Radiographs” not “x-rays”
Radiographs are “shadowgrams”Thickness and composition areimportant
Objectives far from the detector are“magnified”
Anatomy of interest should be asclose to the detector as possible
Thickness is important
Composition is important
Routine posteroanterior (PA) Filmx-rays pass from back to front(organs of interest closest to film)
viewed as if you face the subject(subject’s left on your right)
Digital RadiographyEliminates use of film
Lateral Chest FilmsLeft Lateral used commonly
What is the difference between the two subjects?
Fluoroscopy/Angiography
Real time visualization using x-rays
Continuous beam of x-rays with electronicfluoroscopic detection
Placement of catheters for administrationof contrast material
Iodinated contrast material -- a denseradiopaque material)
Angiography - imaging of the arteries andveins using fluoroscopic techniques
arteriogramsvenograms
Leg Venograms
Kidney Venogram Pulmonary Arteriogram
Digital Subtraction AngiographyBrainLateral View
Superior
AnteriorPosterior
Inferior
Posterior
Aneurysm
Fluoroscopy Safety:Important Role for the Medical
Physicist
Tomography -Thin sections provide improvedradiographic visualization
Computed Tomography
Commercially developed in the1970’s
Unique (transaxial) cross-sectional imagesPencil thin beam of x-rays passes atall angles through one section of thepatient
Ultra-sensitive electronic detectioncomputer used to reconstructtomographic images (Hounsfield -Nobel Prize for medicine)
Images presented as if you wereviewing the patient from the “foot of thebed”
Patient’s right on your left
Tomogramstypical thickness is 5 -10 mmnot projectionsclarity obvious
Multiplanar views accomplished bymoving the subject through the scanner
Permits 3-dimensionalreconstructions
Ultrasound
Imaging with high frequency soundwaves
Sound reflected from tissue interfacessolid organs are echogenic
can’t look “behind” bonecysts (fluid-filled cavities) are anechnotic(echolucent)
US images are not as clear as CT or MRI,but
• Safe (no radiation)• Interactive imaging in any plane• Cheap• Bedside procedure• Permits visualization of movement
Magnetic Resonance Imaging (MRI)Complicated signal detection procedure
Spectroscopic detection of spinresonance detects hydrogen nuclei(mostly from water and fat)
Makes use of magnetic fields
MRI is a tomographic technique• tissue sections• arbitrary imaging planes• excellent depiction of soft tissues
sagittalaxial
coronal
Multislice MRI
Anterior Posterior
Right LateralLeft Lateral
Superior
MRI is intrinsicallymultiparametric
• MRI “Flavors”– Proton density weighted
• Signal intensity depends (mostly) on water(or fat) content
– T1 weighted• Signal intensity depends (mostly) on water
relaxation time T1– T2 weighted
• Signal intensity depends (mostly) on waterrelaxation time T2
• Relaxation times T1 and T2 arenuclear magnetic properties thatdepend on the surrounding physicalstructure (biological tissues)
• MRI “Flavors”– Proton density weighted
• Signal intensity depends (mostly) on water(or fat) content
– T1 weighted• Signal intensity depends (mostly) on water
relaxation time T1– T2 weighted
• Signal intensity depends (mostly) on waterrelaxation time T2
• Relaxation times T1 and T2 arenuclear magnetic properties thatdepend on the surrounding physicalstructure (biological tissues)
T1-weighted MRI(typical)
• Without contrast– T1 is dependent on tissue’s
microscopic structure• With contrast
– Intravenously administeredmaterial that contains electronspins alters the nuclear spinT1
• Without contrast– T1 is dependent on tissue’s
microscopic structure• With contrast
– Intravenously administeredmaterial that contains electronspins alters the nuclear spinT1
Positron EmissionTomography
Positron EmissionTomography
Positron EmissionTomography
• Based on the existence of asubatomic particle called apositron (a positive electron)
• Certain unstable nuclearisotopes emit positrons– Requires an onsite cyclotron
• Emitted positrons move a smalldistance before encountering anegative electron causing decayto two gamma rays
• Based on the existence of asubatomic particle called apositron (a positive electron)
• Certain unstable nuclearisotopes emit positrons– Requires an onsite cyclotron
• Emitted positrons move a smalldistance before encountering anegative electron causing decayto two gamma rays
PET Technique
PET Imaging
PET Tracers• 18Fluorodeoxyglucose (FDG) is a tracer of glucose
metabolism– Injected into vascular system– Transported into cells by glucose transporters– FDG metabolism reaches a ‘dead end’ after
phosphorylation– tracer of glucose metabolism
• H215O
– Injected into the vascular system– Penetrates all membranes– Washout rate depends on cerebral blood flow
• 15O2– Delivered by inhalation– Tracer converted to CO2 by respiration and washed
out by blood flow– Analysis of time course can be used to determine the
rate of oxygen metabolism if a CBF measurement isalso done
• Many other PET tracers are in development– The basis of ‘molecular imaging’
• 18Fluorodeoxyglucose (FDG) is a tracer of glucosemetabolism– Injected into vascular system– Transported into cells by glucose transporters– FDG metabolism reaches a ‘dead end’ after
phosphorylation– tracer of glucose metabolism
• H215O
– Injected into the vascular system– Penetrates all membranes– Washout rate depends on cerebral blood flow
• 15O2– Delivered by inhalation– Tracer converted to CO2 by respiration and washed
out by blood flow– Analysis of time course can be used to determine the
rate of oxygen metabolism if a CBF measurement isalso done
• Many other PET tracers are in development– The basis of ‘molecular imaging’
PET Tracers
PET Safety Issues
• Gamma ray exposure• Chemical safety
– Positron emitters tend to haveshort half lives
– Tracer molecules must besynthesized immediately beforeuse
• Pharmacological effects of thetracer– Many PET tracers are analogs of
drugs or neurotransmitters
• Gamma ray exposure• Chemical safety
– Positron emitters tend to haveshort half lives
– Tracer molecules must besynthesized immediately beforeuse
• Pharmacological effects of thetracer– Many PET tracers are analogs of
drugs or neurotransmitters