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Medical Image Analysis Medical Imaging Modalities Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Anatomical or structural ◦ X-ray radiology, X-ray mammography, X-ray CT, ultrasound, Magnetic Resonance Imaging Functional or metabolic ◦ Functional MRI, (Single Photon Emission Computed Tomography) SPECT, (Positron Emission Tomography) PET, fluorescence imaging Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. X-ray Imaging Figure comes from the Wikipedia, www.wikipedia.org. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Ejected Electron 39 P 50N K L N O X-ray Photon Incident Electron Figure 4.1. Atomic structure of a tungsten atom. An incident electron with energy greater than K-shell binding energy is shown interacting with a K-shell electron for the emission of an X-ray photon. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. X-ray Imaging Tungsten ◦ K-shell binding energy level: 69.5 keV ◦ L-shell binding energy level: 10.2 keV ◦ An emision of X-ray photon of 59.3 keV X-ray generation ◦ Electrons are released by the source cathode and are accelerated toward the target anode in a vacuum under the potential difference ranging from 20,000 to 150,000 volts Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Figure comes from the Wikipedia, www.wikipedia.org. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. X-ray 2-D Projection Imaging Diagnostic radiology ◦ 2-D projection of the three-dimensional anatomical structure of the human body ◦ Localized sum of attenuation coefficients of material: air, blood, tissue, bone ◦ Film or 2-D array of detectors Digital radiographic system ◦ Use scintillation crystals optically coupled with photomultiplier Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. X-ray Source 3-D Object or Patient Anti-scatter Grid X-ray Screen Film X-ray Screen 2-D Projection Image Figure 4.2. (a). A schematic diagram of a 2-D X-ray film-screen radiography system. A 2-D projection image of the 3-D object is shown at the bottom. (b). X-ray radiographic image of a normal male chest. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. X-ray 2-D Projection Imaging Scattering ◦ Create artifacts and artificial structures Reduce scattering ◦ Anti-scattered grids and collimators Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. X-ray Mammography Target material ◦ Molybdenum: K-, L-, M-shell binding energies levels are 20, 2.8, 0.5 keV. The characteristic X-ray radiation is around 17 keV. ◦ Phodium: K-, L-, M-shell binding energies levels are 23, 3.4, 0.6 keV. The characteristic X-ray radiation is around 20 keV. A small focal spot of the order of 0.1mm Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. X-ray Source Compression Device Compressed Breast Moving Anti-scatter Grid X-ray Screen Film X-ray Screen Figure 4.3. A film-screen X-ray mammography imaging system. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Figure 4.4. X-ray film-screen mammography image of a normal breast. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. X-ray Computed Tomography 3-D I out ( y; x, z ) I in ( y; x, z )e ( x , y , z ) dx Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Figure comes from the Wikipedia, www.wikipedia.org. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. y x z X-Y Slices Figure 4.5. 3-D object representation as a stack of 2-D x-y slices. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. y x (x,y; z) 15 z 12 Iin(x; y,z) 22 42 52 62 72 82 92 Iout(x; y,z) 11 Figure 4.6. Source-Detector pair based translation method to scan a selected 2-D slice of a 3-D object to give a projection along the y-direction. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Figure 4.7: The translate-rotate parallel-beam geometry of first generation CT scanners. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. X-ray Computed Tomography Generations ◦ First: an X-ray source-detector pair that was translated in parallel-beam geometry ◦ Second: a fan-beam geometry with a divergent X-ray source and a linear array of detectors. Use translation to cover the object and rotation to obtain additional views Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Generations ◦ Third: a fan-beam geometry with a divergent X-ray source and an arc of detectors. Without translation. Additional views are obtained by simultaneous rotation of the Xray source and detector assembly. “Rotate only” ◦ Fourth: use a detector ring around the object. The X-ray source provides a divergent fan-beam of radiation to cover the object Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Figure 4.8. The first generation X-ray CT scanner Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Ring of Detectors Source Rotation Path Source X-rays Object Figure 4.9. The fourth generation X-ray CT scanner geometry. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Figure 4.10. X-ray CT image of a selected slice of cardiac cavity of a cadaver. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Figure 4.11. The pathological image of the selected slice shown with the Xray CT image in Figure 4.10 Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Magnetic Resonance Imaging Nuclear magnetic resonance ◦ The selected nuclei of the matter of the object ◦ Blood flow and oxygenation ◦ Different parameters: T1 weighted, T2 weighted, Spin-density ◦ Advance: MR Spectroscopy and Functional MRI ◦ Fast signal acquisition of the order of a fraction of a second Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Figure comes from the Wikipedia, www.wikipedia.org. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Figure 4.12. MR images of a selected cross-section that are obtained simultaneously using a specific imaging technique. The images show (from left to right), respectively, the T1-weighted, T-2 weighted and the Spin-Density property of the hydrogen protons present in the brain. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Magnetic Resonance Imaging 1H: high sensitivity and vast occurrence in organic compounds 13C: the key component of all organic 15N: a key component of proteins and DNA 19F: high relative sensitivity 31P: frequent occurrence in organic compounds and moderate relative sensitivity Adapted from the Wikipedia, www.wikipedia.org. MR Spectroscopy Figure comes from the Wikipedia, www.wikipedia.org. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. MR Spectroscopy Figure comes from the Wikipedia, www.wikipedia.org. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Functional MRI Figure comes from the Wikipedia, www.wikipedia.org. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. MRI Principles : spin-lattice relaxation time T2 : spin-spin relaxation time : the spin density T1 Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. MRI Principles 1. Great web sites 1. Simulations from BIGS - Lernhilfe für Physik und Technik 2. http://www.cis.rit.edu/class/schp730/bmri/b mri.htm Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. MRI Principles Spin ◦ A fundamental property of nuclei with odd atomic numbers is the possession of angular moment Magnetic moment ◦ The charged protons create a magnetic field around them and thus act like tiny magnets Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. MRI Principles : the spin angular moment : the magnetic moment : a gyromagnetic ratio, MHz/T J J A hydrogen atom ◦ :42.58 MHz/T Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. N J J S Figure 4.13. Left: A tiny magnet representation of a charged proton with angular moment, J. Right: A symbolic representation of a charged proton with angular moment, J and a magnetic moment, μ. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. MRI Principles Precession of a spinning proton ◦ The interaction between the magnetic moment of nuclei with the external magnetic field ◦ Spin quantum number of a spinning proton: ½ ◦ The energy level of nuclei aligning themselves along the external magnetic field is lower than the energy level of nuclei aligned against the external magnetic field Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Figure 4.14 (a) A symbolic representation of a proton with precession that is experienced by the spinning proton when it is subjected to an external magnetic field. (b) The random orientation of protons in matter with the net zero vector in both longitudinal and transverse directions. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. MRI Principles Equation of motion for isolated spin dJ H 0 H 0k dt J d H 0 k dt Solution: 0 H 0 Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Longitudinal Vector OX at the transverse position X Net Longitudinal Vector: Zero Net Transverse Vector: Zero Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. S Lower Energy Level H0 Higher Energy Level N Figure 4.15 (a). Nuclei aligned under thermal equilibrium in the presence of an external magnetic field. (b). A non-zero net longitudinal vector and a zero transverse vector provided by the nuclei precessing in the presence of an external magnetic field. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. z z H0 Net Zero Transverse Vector Non-zero Net Longitudinal Vector y x y x Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. MRI Principles The precession frequency ◦ Depends on the type of nuclei with a specific gyromagnetic ratio and the intensity of the external magnetic field ◦ This is the frequency on which the nuclei can receive the Radio Frequency (RF) energy to change their states for exhibiting nuclear magnetic resonance ◦ The excited nuclei return to the thermal equilibrium through a process of relaxation emitting energy at the same precession frequency MRI Principles 90-degree pulse ◦ Upon receiving the energy at the Larmor frequency, the transverse vector also changes as nuclei start to precess in phase ◦ Form a net non-zero transverse vector that rotates in the x-y plane perpendicular to the direction of the external magnetic field Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. S z y N x Figure 4.16. The 90-degree pulse causing nuclei to precess in phase with the longitudinal vector shifted clockwise by 90-degrees as a result of the absorption of RF energy at the Larmor frequency. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. MRI Principles 180-degree pulse ◦ If enough energy is supplied, the longitudinal vector can be completely flipped over with a 180-degree clockwise shidf in the direction against the external magnetic field Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. S z y N x Figure 4.17. The 180-degree pulse causing nuclei to precess in phase with the longitudinal vector shifted clockwise by 180-degrees as a result of the absorption of RF energy at the Larmor frequency. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. MRI Principles Relaxation ◦ The energy emitted during the relaxation process induces an electrical signal in a RF coil tuned at the Larmor frequency ◦ The free induction decay of the electromagnetic signal in the PF coil is the basic signal that is used to create MR images ◦ The nuclear excitation forces the net longitudinal and transverse magnetization vectors to move Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. MRI Principles A stationary magnetization vector N M n n 1 The total response of the spin system 0 M x i M y j ( M z M z )k dM M H dt T2 T1 Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. RF Pulse In Phase Spin Relaxation Random Phase (Zero Transverse Vector) Dephasing Figure 4.18. The transverse relaxation process of spinning nuclei. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. MRI Principles The longitudinal and transverse magnetization vectors with respect to the relaxation times M x, y (t ) M x, y (0)et / T2 ei0t M z (t ) M z0 (1 e t / T1 ) M z (0)e t / T1 where M x, y (0) M x ', y ' (0)e i0 p Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Mx,y (t) t Mz (t) t Figure 4.19. (a) Transverse and (b) longitudinal magnetization relaxation after the RF pulse. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. MRI Principles The RF pulse causes nuclear excitation changing the longitudinal and transverse magnetization vectors After the RF pulse is turned off, the excited nuclei go through the relaxation phase emitting the absorbed energy at the same Larmor frequency that can be detected as an electrical signal, called the Free Induction Decay (FID) Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. MRI Principles The NMR spin-echo signal (FID signal) i ( x x y y z z ) S ( x , y , z ) M 0 ( x, y, z )e dxdydz i ( x x y y z z ) ( x, y, z ) M 0 S ( x , y , z )e d x d y d z Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. MR Instrumentation The stationary external magnetic field ◦ Provided by a large superconducting magnet with a typical strength of 0.5 T to 1.5 T ◦ Housing of gradient coils ◦ Good field homogeneity, typically on the order of 10-50 parts per million ◦ A set of shim coils to compensate for the field inhomogeneity Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Gradient Coils Gradient Coils RF Coils Magnet Patient Platform Monitor Data-Acquisition System Figure 4.20. A general schematic diagram of a MR imaging system. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Figure comes from the Wikipedia, www.wikipedia.org. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Figure comes from the Wikipedia, www.wikipedia.org. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. MR Instrumentation An RF coil ◦ To transmit time-varying RF pulses ◦ To receive the radio frequency emissions during the nuclear relaxation phase ◦ Free Induction Decay (FID) in the RF coil Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. MR Pulse Sequences NMR signal ◦ The frequency and the phase Spatial encoding in MR imaging ◦ Frequency encoding and phase encoding Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Sagital y z y Axial y z x x Coronal x z Figure 4.21 (a). Three-dimensional object coordinate system with axial, sagittal and coronal image views. (b): From top left to bottom right: Axial, coronal and sagittal MR images of a human brain. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. MR Pulse Sequences Z Gradient X Gradient Z Gradient Y Gradient 90 RF Pulse (Slice Selection) Phase-Encoding (x-scan selection) 180 RF Pulse (Slice Echo Formation) Frequency Encoding (Read-Out Pulse) Figure 4.22. (a): Three-dimensional spatial encoding for spin-echo MR pulse sequence. (b): A linear gradient field for frequency encoding. (c). A step function based gradient field for phase encoding. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. S External Magnet Linear Gradient Varying Spatially Dependent Larmor Frequency Precessing Nuclei N Phase Encoding Gradient Step Positive Phase Change Negative Phase Change Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. MR Pulse Sequences The phase-encoding gradient ◦ Applied in steps with repeated cycles ◦ If 256 steps are to be applied in the phaseencoding gradient, the readout cycle is repeated 256 times, each time with a specific amount of phase-encoding gradient Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Spin Echo Imaging TE : ◦ Between the application of the 90 degree pulse and the formation of echo (rephasing of nuclei TE / 2 : ◦ Between the 90 degree pulse and 180 degree pulse Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. RF Energy: 90 Deg Pulse Relaxation Dephasing Zero Net Vector: Random Phase In Phase In Phase Rephasing RF Energy: 180 Deg Pulse Echo -Formation Figure 4.23. The transverse relaxation and echo formation of the spin echo MR pulse sequence. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Spin Echo Imaging K-space ◦ The placement of raw frequency data collected through the pulse sequences in a multi-dimensional space ◦ By taking the inverse Fourier transform of the k-space data, an image about the object can be reconstructed in the spatial domain ◦ The NMR signals collected as frequencyencoded echoes can be placed as horizontal lines in the corresponding 2-D k-space Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Figure comes from the Wikipedia, www.wikipedia.org. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Spin Echo Imaging : the cycle repetition time T2 weighted TR ◦ A long TR and a long TE T1 weighted ◦ A short TR and a short TE Spin-density ◦ A long TR and a short TE Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. TE /2 180 deg RF pulse 90 deg RF pulse RF pulse Transmitter Gz: Slice Selection Frequency Encoding Gradient TE /2 Gx: Phase Encoding Gradient Gy: Readout Frequency Encoding Gradient TE NMR RF FID Signal Figure 4.24. A spin echo pulse sequence for MR imaging. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Spin Echo Imaging T R TTE T1 2 ( x, y, z ) 0 ( x, y, z )e 1 e The effective transverse relaxation time from the field inhomogeneities 1 1 H * T2 T2 2 Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Spin Echo Imaging The effective transverse relaxation time from a spatial encoding gradient 1 1 Gd * ** T2 T2 2 Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Echo Planar Imaging A single-shot fast-scanning method Spiral Echo Planar Imaging (SEPI) 1 d Gx (t ) x (t ) dt 1 d G y (t ) y (t ) dt ◦ where x (t ) t cos t y (t ) t sin t 90 deg RF pulse 90 deg RF pulse RF pulse Transmitter Gz: Slice Selection Frequency Encoding Gradient 2 2 2 2 Gx: Oscillating Gradient 2 2 2 2 Gy: Readout Gradient NMR RF FID Signal Figure 4.25. A single shot EPI pulse sequence. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. y gy 2 x gx Figure 4.26. The k-space representation of the EPI scan trajectory. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. y SEPI Trajectory Data Sampling Points x Figure 4.27. The spiral scan trajectory of SEPI pulse sequence in the k-space. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. TE /2 180 deg RF pulse 90 deg RF pulse RF pulse Transmitter Gz: Slice Selection Frequency Encoding Gradient TE /2 Gx Gradient Gy Gradient TE NMR RF FID Signal TD Figure 4.28. The SEPI pulse sequence Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Figure 4.29. MR images of a human brain acquired through SEPI pulse sequence. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Gradient Echo Imaging Fast low angle shot (FLASH) imaging ◦ Utilize low-flip angle RF pulses to create multiple echoes in repeated cycles to collect the data required for image reconstruction ◦ A low-flip angle (as low as 20 degrees) ◦ The readout gradient is inverted to re-phase nuclei leading to the gradient echo during the data acquisition ◦ The entire pulse sequence time is much shorter than the spin echo pulse sequence Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Low Flip Angle RF pulse RF pulse Transmitter Gz: Slice Selection Frequency Encoding Gradient Gx: Phase Encoding Gradient Gy: Readout Frequency Encoding Gradient TE NMR RF FID Signal Figure 4.30. The FLASH pulse sequence for fast MR imaging. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Flow Imaging Tracking flow ◦ Diffusion (incoherent flow) and perfusion (partially coherent flow) ◦ The FID signal generated in the RF receiver coil by the moving nuclei and velocitydependent factors MR angiography Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. TE /2 180 deg (selective) RF pulse 90 deg RF pulse RF pulse Transmitter Gz: Slice Selection Frequency Encoding Gradient Gx: Phase Encoding Gradient Gy: Readout Frequency Encoding Gradient TE NMR RF FID Signal Figure 4.31. A flow imaging pulse sequence with spin echo. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Figure 4.32: Left: A proton density image of a human brain. Right: The corresponding perfusion image. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Next 90 degree RF pulse 90 degree RF pulse RF pulse Transmitter Gz: Slice Selection Frequency Encoding Gradient Gx: Phase Encoding Gradient Gy: Readout Frequency Encoding Gradient TE NMR RF FID Signal TR Figure 4.33. Gradient echo based MR pulse sequence for 3-D MR volume angiography. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Figure 4.34. An MR angiography image. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Nuclear Medicine Imaging Modalities Radioactivity decay N (t ) N (0)e t Half-life of a radionuclide decay Thalf 0.693 Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Nuclear Medicine Imaging Modalities The radioactivity of a radionuclide ◦ The average decay rate dN N dt ◦ Curie (CI) 3.7 1010 disintegrations per second (dps) ◦ Becquerel (Bq) One dps Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Single Photon Emission Computed Tomography Radioisotope ◦ The radioisotopes are injected in the body through administration of radiopharmaceutical drugs that metabolize with the tissue Gamma rays ◦ The gamma rays from the tissue pass through the body and are captured by the detectors surrounding the body to acquire raw data for defining projections Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Figure comes from the Wikipedia, www.wikipedia.org. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Single Photon Emission Computed Tomography Radionuclides ◦ ◦ ◦ ◦ Thallium Technetium Iodine Gallium Gamma ray ◦ Decay by emitting gamma rays with photon energy ranging from 135 keV to 511 keV Attenuation I d I 0 e x Object Emitting Gamma Photons Scintillation Detector Arrays Coupled with Photomultiplier Tubes Figure 4.35. A schematic diagram of detector arrays of SPECT scanner surrounding the patient area. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Single Photon Emission Computed Tomography Scintillation detector ◦ Barium fluoride ◦ Cesium iodide ◦ Bismuth germinate BGO Photomultiplier tube Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Figure 4.36. A 99Tc SPECT image of a human brain Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Single Photon Emission Computed Tomography Attenuation and scattering ◦ Photoelectric absorption and Compton scattering Poor in structural information ◦ Attenuation and scattering Assessment of metastases or characterization of a tumor Lower cost than PET Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Positron Emission Tomography Concept ◦ Simultaneous detection of two 511keV energy photons traveling in the opposite direction Radionuclides ◦ Decay by emitting positive charged particles called positrons ◦ Fluorine 18-F ◦ Oxygen 15-O ◦ Nitrogen 13-N ◦ Carbon 11-C Detector Ring Point of Positron Emission Object Emitting Positrons Coincidence Detection System Computer Point of Positron Annihilation Display Scintillation Detector Arrays Position Dependent Photomultiplier Tubes Figure 4.37. A schemtaic diaggram of PET scanner. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Figure comes from the Wikipedia, www.wikipedia.org. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Positron Emission Tomography After emission ◦ Travel typically for 1-3 mm, losing some of its kinetic energy ◦ The annihilation of the positron with the electron ◦ Cause the formation of two gamma photons with 511keV traveling in opposite directions ◦ Coincidence detection ◦ The point of emission of a positron is different from the point of annihilation with an electron Positron Emission Tomography Radiopharmaceutical ◦ Fluorodeoxyglucose (FDG) ◦ Resolution and sensitivity of PET imaging is significantly better than SPECT Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Figure 4.38: Serial images of a human brain with FDG PET imaging. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Ultrasound Imaging Diagnostic imaging ◦ Anatomical structures, blood flow measurements and tissue characterization ◦ Safety, portability, low-cost Figure comes from the Wikipedia, www.wikipedia.org. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Figure comes from the Wikipedia, www.wikipedia.org. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Ultrasound Imaging Velocity c Relative intensity in dB 10 log 10 I1 I2 Shorter waves ◦ Better imaging resolution Frequencies: 2 MHz to 5 MHz are common Reflection and Transmission Acoustic impedance Z0 c R1, 2 Z 2 Z1 Z1 Z 2 2Z 2 T1, 2 Z1 Z 2 Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Z1 Z3 Z2 Z4 Z5 I0 T1,2 T2,3 T3,4 T5,4 T4,3 T3,2 T2,1 R0 x1 x2 x3 Figure 4.39. A path of a reflected sound wave in a multilayered structure. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Refraction Snell’s law c2 sin t sin i c1 Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Pulse Generation and Timing Acoustic absorbers Blockers Transmitter/ Receiver Circuit Control Circuit Piezoelectric crystal Imaging Object DataAcquisition Analog to Digital Converter Computer Imaging Storage and Processing Display Figure 4.40. A schematic diagram of a conventional ultrasound imaging system. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Figure comes from the Wikipedia, www.wikipedia.org. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Ultrasound Imaging A-mode ◦ Records the amplitude of returning echoes from the tissue boundaries with respect to time ◦ Perpendicular incident angle ◦ Basic method Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Ultrasound Imaging M-mode ◦ Variations in signal amplitude due to object motion ◦ X-axis represents the time, while the y-axis indicates the distance of the echo from the transducer Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Figure 4.41. M-Mode display of mitral valve leaflet of a beating heart. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Ultrasound Imaging B-mode ◦ Two-dimensional images representing the changes in acoustic impedance of the tissue Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Figure 4.42. The “B-Mode” image of a beating heart with mitral stenosis. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Ultrasound Imaging Doppler ultrasound imaging 2 cos f f doppler c Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003. Figure 4.43. A Doppler image of the mitral valve area of a beating heart. Figures 4.4.3-5 are taken from the website http://www2.umdnj.edu/~shindler/ms.html. Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003.
