Medical ImagingSource: uhrad.com.

Medical ImagingSeeing Through the Human Bodyg g y

El A li iElsa AngeliniDepartment TSIENST

1

ENST

It all started in 1845 with the first X-ray image

2Roentgen’s wife Von Kolliker

History of Medical ImagingX

Ray • 1845: Discovery of X-ray by Wilhelm Conrad Röntgen, german physicist.

• 1972: First scanner set up by Allan Mc Cornack et Godfrey N. Hounsfield, Nobel prize in 1979 for this work.

US • 1915: Ultrasound propagation principles for SONAR (SOund NAvigation Ranging).

• 1955: First echography by Inge Edler (1911-2001), swedish cardiologist.

MR

I • 1945: Discovery of nuclear resonance under a magnetic field by Edward Purcell and Felix Bloch, both nobel prize winners in 1952.

• 1973: First MRI image on an animal by the american chemist Paul Lauterbur. P. Lauterbur and P. Mansfield won the Nobel Prize for Physiology or Medicine in 2003 for the development of MRI.

lear

the development of MRI. • 1980: Spectroscopy by magnetic resonance.

• 1934: Discovery of natural radioactivity by Henri Becquerel, Pierre et Marie Curie. Discovery of artificial radioactivity by Irène et Frédéric Joliot-Curie

3

Nuc

l y y y• 1990: Nuclear medicine development with scintigraphy and positron emission

tomography.

Terminology• Transmission: Photons passing through the body• Absorption: Partial or total absorption of energy in the patient• Scatter: Radiation diverted in a new direction

• Transaxial - plane normal to a vector from head to toe. Source: Utrecht University, NL

p• Coronal - plane normal to a vector from front to back • Sagittal - plane normal to a vector from left to right. • Oblique – otherwise

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• Oblique – otherwise.

Imaging Data Types• 2D:

– A single slice.A single slice. • 3D:

A series of parallel slices with uniform– A series of parallel slices with uniform spacing.

– A series of slices with varying spacing– A series of slices with varying spacing and/or orientation.

– A volumetric data set

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A volumetric data set.

Imaging Support

Digital DisplayFilms

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(soft copy)(hard copy)

Imaging Modalities

• X-Ray:– TraditionalTraditional – Computerized Tomography

• Ultrasound• Ultrasound• Magnetic Resonance Imaging (MRI)• Nuclear Imaging

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Conventional X-Ray

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Conventional X-RayX ra sPhysics Principles

• Accelerating & decelerating electrons generate electromagnetic radiation

• Bombardment of a target material with a

X-rays E ≈ 5-150keV

Physics Principles

• Bombardment of a target material with a beam of fast electrons

• Electrons are emitted thermally from a heated cathode (C) and are accelerated t d th d t t (A) b th li d

CAe-

toward the anode target (A) by the applied voltage potential V (~kV).

• Electromagnetic radiation is produced by the quick deceleration of the electrons

+-V = 5-150kV

qwhen hitting the target (bremsstrahlung). – ~99% of energy converted into heat.– Few generated X-ray photons with

wavelength set by the amount of energy E1

hν

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wavelength set by the amount of energy loss E=hν=E2-E1

E1

E2Nucleus

Conventional X-RayI F ti

• X-ray beam goes though th ti t ith d

Image Formation

the patient with decrease energy, function of the absorption pattern inside Primary X-raysabsorption pattern inside the body.

patient

Primary X rays

collimator

10

Screen + detector

Conventional X-RayI C t

• Image captured on h h ith

Image Capture

phosphor screen, with conversion to visible light.

Primary X-• Recording on film

(negative image) patient

lead

Primary Xrays

• Display on video monitor (positive image)

lead

11

(p g )detector

Conventional X-RayS t D iSystem Design

cathodescatters

lead

VERRE BOMBARDE

CONE PLOMBE

HUILE oil

Optical field

12Optical field

Conventional X-RayS t D iSystem Design

13

Conventional X-Ray• Advantages:

• Fast.• Inexpensive.

• Disadvantages:• Ionizing radiation involved.• Projection images.• Poor blood vessel and soft-tissue

contrasts.

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Conventional X-Ray

• Applications:– Lungs, breasts, GI track.Lungs, breasts, GI track.– Blood vessels (contrast agent).– Bones jointsBones, joints.

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Source: http://www.szote.u-szeged.hu/Radiology/Anatomy/

Conventional X-RayExamples: Bones

1 Frontal sinus 11. Mastoid cells12 N h

1. Bifid spinous process of C32. Superimposed articular processes3 Uncinate processes

1. Frontal sinus2. Ethmoidal sinus3. Sphenoidal sinus4. Maxillary sinus5. Anterior clinoid processes6. Hypophyseal fossa7 Posterior clinoid processes

12. Nasopharynx13. Angle of mandible14. Anterior arch of the atlas15. Dens of axis16. Posterior arch of the atlas17. Internal occipital protuberance

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3. Uncinate processes4. Air filled trachea5. Transverse process of C76. Transverse process of T17. 1st rib8. Clavicle

7. Posterior clinoid processes8. Clivus9. Great density of the petrouspart of the temporal bone10. External acoustic meatus

A. Coronal sutureB. Lambdoid sutureC. The grooves for the branches of the middle meningeal vessels

Examples: LungsConventional X-Ray

Patient with hemo-pneumothorax Patient with pacemaker

Pleurall line

air + fluid

17Source: www.mypacs.net

air + fluid

Examples: MammographyConventional X-Ray

p g p y• Low kV can be used (little

attenuation) => sufficient photoelectric absorption tophotoelectric absorption to differentiate between normal tissue and pathology

• Dose must be limited• Dose must be limited.• Breast must be compressed

– To avoid motion.– To minimize focus/film distance.– To have equal tissue thickness.

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Examples: FluoroscopyConventional X-Ray

Examples: Fluoroscopy• Real-time X-ray imaging.

Direct is ali ation on screen• Direct visualization on screen.• Used for guidance of interventions

(mainly vascular and orthopedic).

Ex: Fluoroscopic guidance withEx: Fluoroscopic guidance with umbilical catheter injecting contrast agent in the small bowel

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bowel.

Source: www.mypacs.net

Examples: FluoroscopyConventional X-Ray

Examples: Fluoroscopy

patient

C-arm

Source: Utrecht University NL

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Source: Utrecht University, NL

cathode

C t i d T hComputerized Tomography (CT)(CT)

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CTPh i P i i lPhysics Principles

• Same as X-ray.

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CTI F ti

• Same as X-ray.Image Formation

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CTI C tImage Capture

• Generation of a sliced view of body interior (“T”)

Measure = integral attenuation

of body interior ( T ) (cf. tomos = slice in Greek).• Computational intensive

µ(x,y) ?

• Computational intensive image reconstruction (“C”).

Patient’s body

X

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X-ray source

CTCTI C tImage Capture

• Translation and rotation of integral measure of absorption.

• Backprojection

∫⎛ ⎞

I = Ioexp − µ(x, y)dlL∫

⎛

⎝ ⎜

⎞

⎠ ⎟

=> µtotal = µ(x,y)dl∫ = −ln I⎛ ⎜

⎞ ⎟

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> µtotal µ(x,y)dl

L∫ ln

I0⎝ ⎜

⎠ ⎟

∫⎛ ⎞

g(s,θ)CT

Image Capture: BackprojectionI = Ioexp − µ(x, y)dl

L∫

⎛

⎝ ⎜

⎞

⎠ ⎟

I⎛ ⎜

⎞ ⎟

x’y

sy’

g ≡ ln Io

I⎛ ⎝ ⎜

⎞ ⎠ ⎟ (Signal)

θs

µ(x,y)xunknown

absorption g(s,θ ) = µ(x, y)dlL∫

The Radon transform g(s,θ) of a function µ(x,y) is defined as its line integral along a line inclined at an angle θ from

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as its line integral along a line inclined at an angle θ from the y-axis and at a distance s from the origin.

CTImage Capture: Backprojection

g(s,θ ) = µ(x, y)dlL∫ g(s,θ)L

• The Radon transform maps the spatial domain (x,y) to the domain (s,θ).

x’y

sy’

domain (s,θ).• Each point in the (s,θ) space corresponds to a line in the spatial domain (x,y). x

θµ(x,y)

unknownunknownabsorptiong(s,θ ) = µ(x, y)δ (x cosθ + y sinθ − s)dxdy∫∫

= µ(s cosθ − y' sinθ ,s sinθ + y' cosθ)dy'∫

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µ( y , y ) y∫

2D-frequency domain of µ(x,y)

CTImage Capture: Backprojection

2D-space domain of µ(x y)

µ( ,y)Radon Transform & Projection Theorem (Center slice theorem)

2D-space domain of µ(x,y)

g(s,θ) sy

θ

ωy

θ

s1D-Fourier transform

F( ( ))x

θ

µ(x y)ωx

θF(g(s))

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µ(x,y)

CTImage Capture: Hounsfield Units

• Relates the linear attenuation coefficient of a local region µ to the linear attenuation coefficient of water, µW @ 70 keV (=Eeff).Based on meas rements ith the original EMI scanner in ented b• Based on measurements with the original EMI scanner invented by Hounsfield.

HU = 1000 •µ − µw

µ w

29• Assign calibrated values to gray scale of CT images.

CTS t D i• 1st generation: Original resolution:

80 × 80 pixels (ea. 3 × 3 mm2),

System DesignTranslation & Rotationp ( ),

13mm slice thickness, 5min scan time, 20min reconstruction.

• 2nd generation: reduced number of view angles ⇒ scan time ~30 s.

Translation & Rotation

• 3rd generation: scan time ~seconds (reduced dose, motion artifacts). Reconstruction time only )~seconds.

yRotation

CTS t D i

• 4th generation: scan time, reconstruction time ~sec

System Design

reconstruction time sec.

only Rotation ofonly Rotation of sources

• Spiral: Continuous linear motion of patient table during multiple scans. I d lIncreased coverage volume per rotation.

CTExample: Image quality

20001975

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128x128 pixels, 1-4 hours acquisition, 1-5 days computation

512x512pixels, 0.35 sec aquisition, <1sec computation

CTExample: Lungs

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CTExample: Lungs

Ex: CT of right lung with active pulmonary tuberculosis: shows centrilobular lesions (nodules

b hi li t t 2 4 i di t )or branching linear structures 2-4 mm in diameter) in and around the small airways.

Source: www.mypacs.net

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CTExamples: Abdomen

35Diagnosis of appendicitis

CTExample: Abdomen

TRA CTScout CT Coronal MPR

Virtual d

Source: www.mypacs.net

endoscopy

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CTExample: Blood vessels

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CTExample: Blood Vessels

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CT

39Vitrea©

• Calcium ScoringCT

T t l S S

Calcium Scoring

Hn x-factor(Agatston Scoring)

Total Score = S

(Agatston Scoring)

130-199 1

200 299 2200-299 2

300-399 3

>400 4

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>400 4

Area = 15 mm2

Peak CT = 450Score = 15 x 4 = 60

Area = 8 mm2

Peak CT = 290Score = 8 x 2 = 16

Ultrasound

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UltrasoundPh i P i i lPhysics Principle

• Traveling pressure waves through a medium.

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UltrasoundPh i P i i l

20 Hz 20 kHz 1 MHz 20 MHz

Physics Principle

20 Hz 20 kHz 1 MHz 20 MHzinfra-sound

audible sound ULTRASOUND

DiagnosticDiagnosticUltrasound

Frequency f (Hz)101 102 103 104 105 106 107

flight ~ 1015

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q y ( )flight 10fxray ~ 1018

UltrasoundI F ti

• Sound waves propagate th h th b d

Image FormationN

e

through the body. • At each interface, part is

fl t d t i

ear Field

reflected, part is transmitted.R fl t d

dFar F• Reflected waves are

recorded back.

Field

44Source: The essential physics of Medical Imaging

Ultrasound PulsetransducerUltrasound

I F ti

Echo

Image Formation

Echo

DD

EchoTISSUE D = c×Time/2

c = 1 54 mm/µs

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c = 1.54 mm/µs

UltrasoundImage Captureg p

• Recorded signals:– Specular reflection, Diffuse

scattering, Rayleigh scattering• Frame rate (FR) =number of

times per second a sweep of the ultrasound beam is performed.– The higher the frame rate, the

T_line = 2×D/c

T_frame = N ×Tline = 2 N D/

gbetter the temporal resolution.

– Limited by:• Time delay from maximum depth.

2×N×D/c

FR_max = 1/ Tframe

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• Speed of sound.

Piezoelectric ElementA ti I l t

UltrasoundS t D i Acoustic InsulatorSystem Design Transducer

Backing Material

ElectricConnector

Matching Layer

Backing MaterialPhased array transducer

Di lDisplay

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Ultrasound• Advantages:

– Portable.– Inexpensive.– Good spatial resolution (~1mm).– High temporal resolution.

• Disadvantages:– Poor image quality.– High level of noise.

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UltrasoundS t D iSystem Design

A-modeamplitude displayamplitude display

B-modeB i ht di l

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Brightness display(Gray-scale)

UltrasoundS t D iSystem Design

A-mode B-mode

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UltrasoundApplications

• ObstetricH t

pp

• Heart• GI track (liver, gall bladder, pancreas)• Urinary track (bladder, kidneys) • Genital organs (prostate, testicles,Genital organs (prostate, testicles,

ovaries, uterus). • Blood vessels (Doppler)

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• Blood vessels (Doppler).

Example: Blood vesselsUltrasound

– Establish number of fetus.Check position of placenta

Example: Blood vessels

– Check position of placenta. – Determine fetal age and development.– Check for congenital defects.Check for congenital defects.– Check fetus position.

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Example: ObstetricUltrasound

1961: First image of fetus 1990: First 3D visualization of fetus

Example: Obstetric

fetus

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Example: HeartUltrasound

- Valve diseases.- Cardiac function (pumping efficiency).

Bl d l t i di h b

Example: Heart

- Blood clots in cardiac chamber.

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UltrasoundExample: HeartExample: Heart

55• Real-Time 3D Ultrasound

• Biopsy guidance. Examples: AbdomenUltrasound

p y g• Diagnosis of abdominal pains, kidney stones, inflamed appendicitis. kidney

Examples: Abdomen

appendicitis

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liver

Example: Blood vesselsUltrasound

• Artery blockage from blood clots.• Arteriosclerosis (plaques).• Stent position

Example: Blood vessels

• Stent position

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UltrasoundUltrasoundExample: Blood vessels

• DopplerExample: Blood vessels

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Magnetic Resonance ImagingMagnetic Resonance Imaging(MRI)

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MRIPh i P i i l

• Nuclei with magnetic dipoles (H)Physics Principle

No magnetic field Magnetic field

(H). • Magnetic field B0 makes nuclei precess along its

directiondirection.• The precession rateis the Larmor frequency.

• f = γ B (43×1 5 = 64 MHz for• fL = γ B0 (43×1.5 = 64 MHz for Hydrogen into a 1.5T magnet).

B0

z

60

0

Source: Hielscher, Columbia Univ.

MRIImage Formation • Nuclei with magnetic dipole moment µ,g

En

erg

y

mz = +1/2

B0

z

g p µ,and angular momentum S.• Net magnetization M = density of µ.

• Tip M away from B ⇨ Precession atE e y

mz = -1/2

Spin flip

∆Ε = γΒ0

• Tip M away from B0 ⇨ Precession at frequency γB0, producing a measurable RF magnetic field.

Z

J or µ or MB0

• For every 1,000,000 nuclei in upper state|B

transition

Y

For every 1,000,000 nuclei in upper state (mz=+1/2) there are 1,000,001 nuclei in lower state (mz=-1/2).

• This difference is enough to result in i t ti ti f t i l

B0|

61

Y

X

|B0|×γ×tmacroscopic net magnetization of material.

Image CaptureMRI

• As the magnetization precesses it creates its own RF magnetic field.

• This field is much smaller than the exciting RF field

Z

J or µ or MB0

exciting RF field.• It can be detected with a standard radio

receiver (e.g. RF coils used to tip M away from B0)

J or µ or M

from B0)• The resulting signal from precession is

called the Free Induction Decay or FID.Y

X

|B0|×γ×t

X

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MRISystem Design• Main Magnet

– High, constant,Uniform Field, B

B0B0.

• Gradient CoilsProduce pulsed linear gradients in

B0– Produce pulsed, linear gradients in this field: Gx, Gy, & Gz

• RF coils B1RF coils– Transmitter: B1 Excites NMR signal

to generate Free Induction Decay ( FID)

B0

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FID).– Receiver: Senses FID.

MRISystem Design

Magnet + shielding + cooling systems

gantry

64

g y

MRI• Advantages:

– High image quality.– Good spatial resolution (~1mm).– All tissues (except lung).

• Disadvantages:– Very expensive scanners.– Some patients cannot be imaged

(pacemaker, claustrophobia).

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MRIApplications

• Brain (Multiple sclerosis, Alzheimer’s disease epilepsy tumors)

pp

disease, epilepsy, tumors) • Spine• Muscles, tendons. • Blood vessels: angiography (strokes,

aneurism)• Heart• Heart• soft tissues

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Example: HeartMRI

• CINE MRIExample: Heart

67

Courtesy of Robert R. Edelman

Example: HeartMRI

Example: Heart

68MRI for myocardial perfusion

Example: Blood vesselsMRI

M ti R

Example: Blood vessels

Magnetic Resonance Angiography

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Example: Blood vesselsMRI

Example: Blood vessels

70Aorta

Example: BrainMRI

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Example: BrainMRI

• Diagnosis of Alzheimer’s and Parkinson’s disease.Example: Brain

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Example: Blood vesselsMRI

Example: Blood vessels

MR Angiography

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Nuclear Imaging (PET & SPECT)(PET & SPECT)

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Nuclear ImagingPh i P i i l PETPhysics Principle: PET

Nuclear imaging is the use of radioactive materials forimaging structures and function inside the bodyimaging structures and function inside the body.

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Nuclear ImagingPh i P i i l PETPhysics Principle: PET• In unstable nucleus, (more protons than neutrons) proton converts to neutron under emission of positronconverts to neutron under emission of positron.

• Positron travels limited distance in tissue.

• Positron can combine with electron of nearby atom and emits two 511 keV X-ray photons (γ rays) that travel in opposite direction.pp

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Nuclear ImagingI C t PETImage Capture: PET

Anger Camera

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Nuclear ImagingI C t PETImage Capture: PET

78

Nuclear ImagingI C t SPECTImage Capture: SPECT

79

Nuclear ImagingI C t SPECTImage Capture: SPECT

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Nuclear ImagingS t D i PETSystem Design: PET

PM: photo multiplier

81

Nuclear ImagingS t D i SPECT

unknownactivity & absorption

• Coincidence occurs with simultaneous detection of

System Design: SPECTα(x,y) ,µ(x,y)

activity & absorptioncross-section

)simultaneous detection of 2 opposite detectors.

• Number of counts at the detectors gives the line

I(σ,

θ)

L1Ldetectors gives the line

integral• Use standard

t h

max max

g( , ) ( , )exp ( ,L L

s x y x ydl dlθ α µ⎛ ⎞

= −⎜ ⎟⎝ ⎠

∫ ∫

Lmax

tomography reconstruction algorithm or statistical approaches (EM)

min 1L L⎝ ⎠∫ ∫

problem is ill-posed! ⇒ different combinations of

d

82

(EM). α and µcan yield identical

measurements

Nuclear Imaging

• Advantages– Functional imaging.g g

• Disadvantages– Poor spatial resolution (~8mm)Poor spatial resolution ( 8mm).– High level of noise.

Expensive hardware– Expensive hardware.– Need of cyclotron.

83

Nuclear ImagingApplications

• HeartL

pp

• Lungs• Kidneys

Bladder• Bladder• GI Track• Endocrine system (hormones)• Endocrine system (hormones)• Immune system (white blood cells).

84

Whole BodyNuclear Imaging

Clinical History: A 71year-old male with history of lung carcinoma, now with bilateral pulmonary nodules and mediastinal

Figure 1. Whole-body gallium-67 scan showing lymphoma in the chest, the spleen, the abdomen, and the groin. The chest and spleen sites were known before the scan. The abdominal and groin uptakes were detected

pulmonary nodules and mediastinal adenopathy.Findings: Bone Scan: Increased radiopharmaceutical uptake along cortical margins of the bilateral femurs and tibias. No evidence of bony metastases

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abdominal and groin uptakes were detected only by the scan.Source: http://www.nucmednet.com/galymph.htm

evidence of bony metastases.

Diagnosis: Hypertrophic osteoarthropathy

http://www.uhrad.com/spectarc.htm

Example: LungNuclear Imaging

SPECT scan for lung perfusion (pulmonary embolism)

86Source: Brigham & women’s Hospital

Example: HeartNuclear Imaging

• Perfusion ImagingStress exams

Example: Heart

Stress exams

Abnormal blood flow

Stress

Normal blood flow Rest

87

Example: BrainNuclear Imaging

Example: Brain

88Source: www.med.harvard.edu/AANLIB

Example: BrainNuclear Imaging

Example: Brain

89Source: www.med.harvard.edu/AANLIB

Example: BrainNuclear Imaging

PET with FDG tracer for diagnosis of brain tumorExample: Brain

90Source: V. Cunningham, GlaxoSmithKline.

Example: BrainNuclear Imaging

Example: BrainPET for in-vivo testing of new drugs

91Source: V. Cunningham, GlaxoSmithKline.

Research in MedicalResearch in Medical Imaging

92

Research in Medical Imaging• Topics• Topics

– Improve image quality.– Extraction of organ contours.– Quantitative measures on organs (volume, cardiac

function, deformations, contractility,…).– Modelization of organs.– Validation of image information for diagnosis.– Tumor detection.– Functional analysis neuroscienceFunctional analysis, neuroscience.

• Tools:– Computers, mathematics, programming, biology,

physics clinical studies

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physics, clinical studies.

Example: Denoising of 3DRX i t d

Research in Medical Imagingspine study

Original Gaussian filtering

94Adaptive Wavelet

ThresholdingWavelet

ThresholdingDenoising Application

Example: Registration of MRI d PET bd i

Research in Medical Imagingand PET abdomen images

95

Example: Segmentation of ti l b i t t

Research in Medical Imagingcortical brain structures

96

Example: Segmentation of b ti l t t

Research in Medical Imagingsub-cortical structures

Lateral ventricles

Third ventricleThird ventricle

Caudate nucleus

Thalam sThalamus

97

Example: Segmentation of b ti l t t

Research in Medical Imagingsub-cortical structures

98

Example: Diffusion Tensor MRI f B i Whit M tt Fib

Research in Medical Imagingfor Brain White Matter Fibers

99

Example: Functional Brain MRIResearch in Medical Imaging

Example: Functional Brain MRI

Motor control of fingers

100

Example: Functional MRIResearch in Medical Imaging

Example: Functional MRI

101Motor control of right hand

Example: Fetal ImagingResearch in Medical Imaging

Example: Fetal Imaging

102

Example: Fetal ImagingResearch in Medical Imaging

Example: Fetal Imaging

103

Books•Foundation of Medical Imaging, Z.H. Cho, J.P. Jones, M. Singh, John Wiley &Sons, Inc., New York 1993, ISBN 0-471-54573-254573-2.

•Principles of Medical Imaging, K.K. Shung, M.B. Smith, B. Tsui, Academic Press, San Diego 1992, ISBN 0-12-640970-6.Tsui, Academic Press, San Diego 1992, ISBN 0 12 640970 6.

•The Essential Physics of Medical Imaging (2nd Edition) ,Jerrold T. Bushberg, J. Anthony Seibert, Edwin M. Leidholdt Jr., John M. Boone, Lippincott Williams & Wilkins; 2nd edition, ISBN 0683301187.

I R i i R di l J A P k CRS P•Image Reconstruction in Radiology, J.A. Parker, CRS Press, Boca Raton, FL 1990, ISBN 0-8493-0150-5/90.

•Principles of Magnetic Resonance Imaging Zhi Pei Liang

104

•Principles of Magnetic Resonance Imaging, Zhi-Pei Liang, P.C. Lauterbur IEEE Press, New York, NY 2000, ISBN 0-7803-4723-4.