Lecture-6
Biosciences (BSE 102)
22/01/2025
Antibiotics
Medical imaging modalities
Microscope
Digital X-ray imaging Computed tomography (CT) imaging
Ultrasound
Nuclear medicine imaging (SPECT and PET) Magnetic resonance imaging (MRI)
Medical imaging?
• Medical imaging refers to several
different technologies that are used to
view inside of the human body non-
invasively in order to diagnose,
monitor, or treat medical conditions.
Nuclear
X-ray CT MRI Ultrasound medicine
RSNA
Imaging planes
• Sagittal plane: a vertical plane that
divides the body into right and left
parts.
Arrow
• Coronal plane: a vertical plane that
divides the body into anterior (front)
and posterior (back) sections.
Crown
• Axial (Transverse): horizontal plane
that divides the body into the upper
and lower section.
Axle
X-ray imaging
➢Most used imaging modality
➢Low-cost, ionizing radiation
➢Good contrast between bone and tissue
➢X-ray energies of 25 keV to 500 keV used for
medical imaging.
➢Used to screen for pneumonia, heart disease,
lung disease, bone fractures, cancer, and
vascular diseases.
➢Computed tomography (CT), fluoroscopy,
mammography, digital subtraction angiography
X-ray imaging system (projection radiography)
• Wilhelm Röntgen and Nobel prize in 1901.
• X-ray images represent the transmission of the X-ray beam through the
patient, weighted by the integrated loss of beam energy due to
scattering and absorption in the body.
Ionization chamber
(automatic exposure Grid
Beam restrictors control)
ADC
X-ray generator
X-ray detectors
X-ray generation
3–5 A at 6–12 V
X-ray
Tube voltage = 30–150 kVp
X-rays interactions Photoelectric effect
➢ The incident photon is completely absorbed by
the atom (usually a K-shell electron), and the
ejected electron is called a photoelectron. Compton scattering
➢ The incident photon ejects a valence (outer-
shell) electron, yielding a new energetic
electron called a Compton electron.
➢ Attenuation is the process describing the loss
of strength of a beam of EM radiation.
➢ Tissue-dependent attenuation is the primary
mechanism by which contrast is created in
radiography modalities. 𝑥
𝐼 𝑥 = 𝐼𝑜 exp{− න 𝜇 𝑥 ′ 𝑑𝑥 ′ }
0
Example problem
A slab of soft tissue with one blood vessel running in the middle is
imaged using an x-ray imaging system. For ease of computation,
assume the tissue and the vessel both have square-shaped cross
sections; the dimensions are shown in the figure. Assume that the x-
ray source produces 𝑁𝑖 = 4 × 106 photons at either 15 keV or 40
keV, and the photons are uniformly shed upon the side of the tissue.
Ignore noise, scattering, and other effects.
Linear attenuation
A. Determine the total number of exiting photons at the two energy coefficient (μ, 1/cm)
levels respectively. At which energy level are more photons Energy Soft blood
absorbed? (keV) tissue
15 4 3
At 15 KeV, 𝑁𝑡 = 1559 40 0.4 0.2
At 40 KeV, 𝑁𝑡 = 1.84 × 106
Maximum allowed radiation dose
Film badge dosimeter
Sievert (Sv)
https://www.aerb.gov.in/english/radiation-protection-principle
Computed Tomography (CT)
➢Lack of depth resolution in X-rays
Tomos – slice, Graphy – write
• Planar x-rays imaging repeated for different
angles, then the reconstruction algorithms are
used to obtain final image.
• The first patient brain scan was done in October
1971.
• Hounsfield and Cormack got the Nobel Prize in
1979.
• CT number was measured in Hounsfield unit.
CT scanner generations
1G scanner 2G scanner 3G scanner 4G scanner
Advanced CT scanners
https://howradiologyworks.com/ctgenerations/
Nuclear medicine imaging
➢Morphology (Transmission) vs Emission (Function) imaging.
https://www.youtube.com/watch?v=hTz_rGP4v9Y
https://www.youtube.com/watch?v=l9swbAtRRbg
https://www.youtube.com/watch?v=GHLBcCv4rqk
