physics of radiology lior copel, m.d. assaf harofeh medical center, zerifin sackler school of...
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Physics of RadiologyPhysics of Radiology
Lior Copel, M.D.Lior Copel, M.D.Assaf Harofeh Medical Center, ZerifinAssaf Harofeh Medical Center, Zerifin
Sackler School of Medicine, Sackler School of Medicine,
Tel-Aviv UniversityTel-Aviv University
Clinical CaseClinical Case
Jaundice and FeverJaundice and Fever
• Subjective:– 42 year old female– Malaise and jaundice for 2 months– Fever for 1 week
• Objective:– Fever – 38.5– Leukocytes – 16700 ; PMN – 78%– Skin and corneal jaundice: Total bilirubin – 11.3 mg/dL Direct bilirubin – 6.7 mg/dL
DiagnosisDiagnosis
• Pancreatic adenocarcinoma (head)
• Obstructive jaundice
• Ascending cholangitis due to obstructive jaundice
Conventional RadiologyConventional Radiology
The Electromagnetic SpectrumThe Electromagnetic Spectrum
PhotonsPhotons
• Electromagnetic radiation is quantized in discrete quantities called photons
• Photons behave as waves or particles but have no mass
• Photons energy (E) – Frequency
Wavelength
• C = velocity of light = 300,000 km/sec
E = h x f = h x (C / λ)
PhotonsPhotons
• Photons X-Rays
• Photons – high energy - 20 – 200 keV
short wavelength - 10-10 m
X-Ray TubeX-Ray Tube
X-Ray Interaction in MaterialX-Ray Interaction in Material
• Pass through (penetrate)
• Absorbed (transfer energy to the absorbed medium)
• Scattered (change direction and possibly lose energy)
The Cassette The Cassette
Radiology Examination Room Radiology Examination Room
X-Ray Advantages X-Ray Advantages
• Excellent imaging of the chest and skeleton
• Good evaluation of GIT and GUT
• Good spatial resolution
• Can be performed dynamically
• Availability
• Relative low radiation dose to patient
X-Ray Disadvantages X-Ray Disadvantages
• Poor 3D geometry
• Poor soft tissue resolution
• Insensitive to small lesions (esp. lung fields)
• No evaluation of CNS and PNS
Ultrasound (US)Ultrasound (US)
Natural UltrasoundNatural Ultrasound
Sound WaveSound Wave
Sound WavesSound Waves
• Infrasound - < 20 Hz
• Audible sound – 15 – 20,000 Hz
• Diagnostic ultrasound – 1 – 20 MHz
(1 MHz = 106 Hz)
• Diagnostic US uses transducers for the production of the waves
Velocity of the US Wave in Different TissuesVelocity of the US Wave in Different Tissues
Doppler PhysicsDoppler Physics
• Doppler effect – the change in frequency that results from a moving sample
• Object Movement:– Toward the detector higher frequency,
lower wavelength– Away from the detector lower frequency,
higher wavelength
Doppler ShiftDoppler Shift
US - AdvantagesUS - Advantages
• Excellent soft tissue contrast resolution
• Dynamic
• No radiation
• Safe in pregnancy
• Available, cheap
US - DisadvantagesUS - Disadvantages
• Operator dependent not imagined-not seen !
• Relatively no anatomic landmarks
• Cannot penetrate air and bone
• No imaging of lungs, CNS, PNS and GIT
Computed Tomography (CT)Computed Tomography (CT)
Computed TomographyComputed Tomography
• Tomography – Greek:– tomos slice or section– graphein to write or record
• CT scan – a diagnostic test that combines X-rays with computer technology
• A series of X-rays from many different angles are used to create a cross-sectional image of the patient’s body
Computed TomographyComputed Tomography
• Reconstruction “builds” the CT image from the data collected and represents a cross section of the patient
Computed TomographyComputed Tomography
• Four hardware components:
– Radiation source
– Radiation detector system
– Mechanical manipulator
– Computer with display
Contrast-Enhanced CTContrast-Enhanced CT
• Abnormal tissues (e.g. tumor, inflammation) enhance differently than normal tissues with IV contrast. This enables the abnormal tissue to be identified and characterized
• Contrast media opacify specific structures (blood vessels, liver, spleen and the urinary tract) enabling abnormal findings to be detected in those structures
Hounsfield UnitsHounsfield Units
The GantryThe Gantry
PROPOSALS FOR THE IONISING RADIATION(MEDICAL EXPOSURE) REGULATIONS 1999
REPIACINGThe Ionising Radiation (Protection of Persons Undergoing Medical
Examination or Treatment) Regulations 1988
CONSULTATIVE DOCUMENT
Comments to be sent to:Ms P M Brown
Room 525 Wellington House133-155 Waterloo Road
London SEI 8UGNo later than 31 May 1999
DEPARTMENT OF HEALTH MARCH 1999
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Diagnostic procedure
Typical Effective Dose (mSv)
Equiv. No. of chest x-rays
Approx. equiv. Period of natural background radiation
X-ray examinations: Limbs and joints (except hip)
<0.01 <0.5 <1.5 days
Chest (single PA film) 0.02 1 3 days Skull 0.07 3.5 11 days Thoracic spine 0.7 35 4 months Lumbar spine 1.3 65 7 months Hip 0.3 15 7 weeks Pelvis 0.7 35 4 months Abdomen 1.0 50 6 months IVU 2.5 125 14 months Barium swallow 1.5 75 8 months Barium meal 3 150 16 months Barium follow through 3 150 16 months Barium encma 7 350 3.2 years CT head 2.3 115 1 year CT chest 8 400 3.6 years CT abdomen or pelvis 10 500 4.5 years
CT - AdvantagesCT - Advantages
• Excellent anatomical data
• Excellent spatial resolution
• Good contrast resolution (fair in CNS and MSK imaging)
• Reconstructions (MPR, MIP, VR, navigation)
• Fast exam (20sec.- 1min.)
• Available
CT - DisadvantagesCT - Disadvantages
• Radiation dose
• Reactions to contrast material
• Static exam
• Availability
• Cost
Magnetic Resonance Imaging (MRI)Magnetic Resonance Imaging (MRI)
Magnetic Resonance ImagingMagnetic Resonance Imaging
• Concept – 1970• Present – 60 million
examinations per year
Hydrogen NucleiHydrogen Nuclei
The Hydrogen NucleiThe Hydrogen Nuclei
• Have the largest magnetic moment
• Abundant in the body
• 1023 H protons in each 1 cm3 of tissue
• These protons are normally randomly oriented and have no net magnetic moment (magnetization vector)
The Hydrogen NucleiThe Hydrogen Nuclei
Hydrogen Nuclei in NatureHydrogen Nuclei in Nature
1 Tesla = 10,000 gauss (G)Earth’s magnetic field 50 µT (0.5 gauss)MRI magnet is 20,000 more powerful than earth’s magnetic field
The MagnetThe Magnet
Protons in a Magnetic FieldProtons in a Magnetic Field
Protons in a Magnetic FieldProtons in a Magnetic Field
90 Degree RF Pulse90 Degree RF Pulse
90 Degree RF Pulse90 Degree RF Pulse
Time Constants MeasurementsTime Constants Measurements
• T1T1 – Time to recover longitudinal magnetization – Realigning to B0 – Range 200 – 2000 msec
• T2T2 – Time to dephase loose horizontal magnetization – Range 30 – 500 msec
• Differences in T1 and T2 provide basis for Differences in T1 and T2 provide basis for variations in signal intensities and tissue contrastvariations in signal intensities and tissue contrast
The time it takes to each tissue to return to its steady state position is the base for MR imaging
T1 Relaxation TimeT1 Relaxation Time
T2 Relaxation TimeT2 Relaxation Time
Relaxation TimeRelaxation Time
• Different tissues return to equilibrium in different time
• Those difference in relaxation time enables different contrast resolution to different tissues and make it possible to differentiate normal tissue from abnormal one
Contrast Agents – Gadolinium-DTPAContrast Agents – Gadolinium-DTPA
• Abnormal tissues (e.g. tumor, inflammation) enhance differently than normal tissues with iv contrast. This enables the abnormal tissue to be identified and characterized
• Contrast media opacify specific structures (blood vessels, liver, spleen and the urinary tract) enabling abnormal findings to be detected in those structures
Planes of ImagingPlanes of Imaging
• Coronal
• Sagittal
• Axial (Horizontal)
MRI Advantages MRI Advantages
• Excellent contrast resolution (esp. CNS, MSK, mediastinum, pelvis and heart)
• Each tissue / pathology can be evaluated with different sequences
• No radiation
MRI AdvantagesMRI Advantages
• Multiplanar imaging
• Can be performed in pregnancy (not in first trimester)
• No risk with contrast materials
• Can be performed dynamically
MRI DisadvantagesMRI Disadvantages
• Problem with cortical bone and calcifications
• Hazard to patients with metallic objects
• Problems in trauma and ventilated patients
• Claustrophobia
• Long examination
• Availability
• Expensive
Be Careful !!!Be Careful !!!