Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

Mri physics

16,332 views

Published on

Published in: Health & Medicine, Technology
  • DOWNLOAD FULL BOOKS, INTO AVAILABLE FORMAT ......................................................................................................................... ......................................................................................................................... 1.DOWNLOAD FULL. PDF EBOOK here { https://tinyurl.com/y6a5rkg5 } ......................................................................................................................... 1.DOWNLOAD FULL. EPUB Ebook here { https://tinyurl.com/y6a5rkg5 } ......................................................................................................................... 1.DOWNLOAD FULL. doc Ebook here { https://tinyurl.com/y6a5rkg5 } ......................................................................................................................... 1.DOWNLOAD FULL. PDF EBOOK here { https://tinyurl.com/y6a5rkg5 } ......................................................................................................................... 1.DOWNLOAD FULL. EPUB Ebook here { https://tinyurl.com/y6a5rkg5 } ......................................................................................................................... 1.DOWNLOAD FULL. doc Ebook here { https://tinyurl.com/y6a5rkg5 } ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... .............. Browse by Genre Available eBooks ......................................................................................................................... Art, Biography, Business, Chick Lit, Children's, Christian, Classics, Comics, Contemporary, Cookbooks, Crime, Ebooks, Fantasy, Fiction, Graphic Novels, Historical Fiction, History, Horror, Humor And Comedy, Manga, Memoir, Music, Mystery, Non Fiction, Paranormal, Philosophy, Poetry, Psychology, Religion, Romance, Science, Science Fiction, Self Help, Suspense, Spirituality, Sports, Thriller, Travel, Young Adult,
       Reply 
    Are you sure you want to  Yes  No
    Your message goes here
  • DOWNLOAD FULL BOOKS, INTO AVAILABLE FORMAT ......................................................................................................................... ......................................................................................................................... 1.DOWNLOAD FULL. PDF EBOOK here { https://tinyurl.com/y6a5rkg5 } ......................................................................................................................... 1.DOWNLOAD FULL. EPUB Ebook here { https://tinyurl.com/y6a5rkg5 } ......................................................................................................................... 1.DOWNLOAD FULL. doc Ebook here { https://tinyurl.com/y6a5rkg5 } ......................................................................................................................... 1.DOWNLOAD FULL. PDF EBOOK here { https://tinyurl.com/y6a5rkg5 } ......................................................................................................................... 1.DOWNLOAD FULL. EPUB Ebook here { https://tinyurl.com/y6a5rkg5 } ......................................................................................................................... 1.DOWNLOAD FULL. doc Ebook here { https://tinyurl.com/y6a5rkg5 } ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... .............. Browse by Genre Available eBooks ......................................................................................................................... Art, Biography, Business, Chick Lit, Children's, Christian, Classics, Comics, Contemporary, Cookbooks, Crime, Ebooks, Fantasy, Fiction, Graphic Novels, Historical Fiction, History, Horror, Humor And Comedy, Manga, Memoir, Music, Mystery, Non Fiction, Paranormal, Philosophy, Poetry, Psychology, Religion, Romance, Science, Science Fiction, Self Help, Suspense, Spirituality, Sports, Thriller, Travel, Young Adult,
       Reply 
    Are you sure you want to  Yes  No
    Your message goes here
  • DOWNLOAD FULL BOOKS, INTO AVAILABLE FORMAT ......................................................................................................................... ......................................................................................................................... 1.DOWNLOAD FULL. PDF EBOOK here { https://tinyurl.com/y8nn3gmc } ......................................................................................................................... 1.DOWNLOAD FULL. EPUB Ebook here { https://tinyurl.com/y8nn3gmc } ......................................................................................................................... 1.DOWNLOAD FULL. doc Ebook here { https://tinyurl.com/y8nn3gmc } ......................................................................................................................... 1.DOWNLOAD FULL. PDF EBOOK here { https://tinyurl.com/y8nn3gmc } ......................................................................................................................... 1.DOWNLOAD FULL. EPUB Ebook here { https://tinyurl.com/y8nn3gmc } ......................................................................................................................... 1.DOWNLOAD FULL. doc Ebook here { https://tinyurl.com/y8nn3gmc } ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... .............. Browse by Genre Available eBooks ......................................................................................................................... Art, Biography, Business, Chick Lit, Children's, Christian, Classics, Comics, Contemporary, Cookbooks, Crime, Ebooks, Fantasy, Fiction, Graphic Novels, Historical Fiction, History, Horror, Humor And Comedy, Manga, Memoir, Music, Mystery, Non Fiction, Paranormal, Philosophy, Poetry, Psychology, Religion, Romance, Science, Science Fiction, Self Help, Suspense, Spirituality, Sports, Thriller, Travel, Young Adult,
       Reply 
    Are you sure you want to  Yes  No
    Your message goes here
  • DOWNLOAD FULL BOOKS, INTO AVAILABLE FORMAT ......................................................................................................................... ......................................................................................................................... 1.DOWNLOAD FULL. PDF EBOOK here { https://tinyurl.com/y8nn3gmc } ......................................................................................................................... 1.DOWNLOAD FULL. EPUB Ebook here { https://tinyurl.com/y8nn3gmc } ......................................................................................................................... 1.DOWNLOAD FULL. doc Ebook here { https://tinyurl.com/y8nn3gmc } ......................................................................................................................... 1.DOWNLOAD FULL. PDF EBOOK here { https://tinyurl.com/y8nn3gmc } ......................................................................................................................... 1.DOWNLOAD FULL. EPUB Ebook here { https://tinyurl.com/y8nn3gmc } ......................................................................................................................... 1.DOWNLOAD FULL. doc Ebook here { https://tinyurl.com/y8nn3gmc } ......................................................................................................................... ......................................................................................................................... ......................................................................................................................... .............. Browse by Genre Available eBooks ......................................................................................................................... Art, Biography, Business, Chick Lit, Children's, Christian, Classics, Comics, Contemporary, Cookbooks, Crime, Ebooks, Fantasy, Fiction, Graphic Novels, Historical Fiction, History, Horror, Humor And Comedy, Manga, Memoir, Music, Mystery, Non Fiction, Paranormal, Philosophy, Poetry, Psychology, Religion, Romance, Science, Science Fiction, Self Help, Suspense, Spirituality, Sports, Thriller, Travel, Young Adult,
       Reply 
    Are you sure you want to  Yes  No
    Your message goes here
  • Great presentation, the most clear amongst all MRI presentation I have seen. Thank you very much!
       Reply 
    Are you sure you want to  Yes  No
    Your message goes here

Mri physics

  1. 1. MRI PHYSICS
  2. 2. PEHCHAN KAUN
  3. 3. NOBEL PRIZE 2003 PETERMANSFIELD Paul lauterbur
  4. 4. MRI: What is it? Magnetic Resonance Imaging Magnet Radio Frequency = Resonance Imaging
  5. 5. • NMR measures the net magnetization of atomic nuclei in the presence of magnetic fields • Magnetization can be manipulated by changing the magnetic field environment (static, gradient, and RF fields) • Static magnetic fields don’t change (< 0.1 ppm / hr): The main field is static and (nearly) homogeneous • RF (radio frequency) fields are electromagnetic fields that oscillate at radio frequencies (tens of millions of times per second) • Gradient magnetic fields change gradually over space and can change quickly over time (thousands of times per second)
  6. 6. WE ARE MAGNETS! Really?
  7. 7. • The adult human body is ~53% water, and water is ~11% hydrogen by mass but ~67% hydrogen by atomic percent. • Thus, most of the mass of the human body is oxygen, but most of the atoms in the human body are hydrogen atoms. • The average 70 kg adult human body contains approximately 3 x 1027 atoms of which 67% are hydrogen atoms!!!!
  8. 8. Why the fuss about hydrogen? • Nucleus needs to have 2 properties: – Spin – charge • Nuclei are made of protons and neutrons – Both have spin ½ – Protons have charge • Pairs of spins tend to cancel, so only atoms with an odd number of protons or neutrons have spin – Good MR nuclei are 1H, 13C, 19F, 23Na, 31P
  9. 9. Y HYDROGEN?? Cont… • Simplest element with atomic number of 1 and atomic weight of 1 • When in ionic state (H+), it is nothing but a proton. • Proton is not only positively charged, but also has magnetic spin (wobble)! • MRI utilizes this magnetic spin property of protons of hydrogen to elicit images!! • We are magnets!
  10. 10. A Single Proton There is electric charge on the surface of the proton, thus creating a small current loop and generating magnetic moment . J + + The proton also has mass which generates an angular momentum J when it is spinning. + Thus proton “magnet” differs from the magnetic bar in that it also possesses angular momentum caused by spinning.
  11. 11. SPIN!! • Protons and neutron spins are known as nuclear spins. • An unpaired component has a spin of ½ and two particles with opposite spins cancel one another. • In NMR it is the unpaired nuclear spins that produce a signal in a magnetic field
  12. 12. But why we can’t act like magnets? • The protons (i.e. Hydrogen ions) in body are spinning in a haphazard fashion, and cancel all the magnetism. That is our natural state! • We need to discipline them first, how?
  13. 13. • When placed in a large magnetic field, hydrogen atoms have a strong tendency to align in the direction of the magnetic field • Inside the bore of the scanner, the magnetic field runs down the center of the tube in which the patient is placed, so the hydrogen protons will line up in either the direction of the feet or the head. • The majority will cancel each other, but the net number of protons is sufficient to produce an image. 5-spin down 7spin up
  14. 14. Precession • The static field causes the spinning proton to ‘wobble’ in a regular manner called ‘PRECESSION’
  15. 15. LARMOR EQUATION
  16. 16. TIME TO WAKE UP… REGARDING MRI SAY TRUE/FALSE • The gyro magnetic ratio of a hydrogen atom is 42.57MHz/T • The strength of magnetic field is measured in gauss • The Larmor frequency is defined as SUM of the magnetic field and gyromagnetic ratio. • An MR active nucleus spins at its own precessional frequency. • ONLY hydrogen nuclei are said to be MR active
  17. 17. SACH KA SAMNA…. REGARDING MRI SAY TRUE/FALSE • The gyro magnetic ratio of a hydrogen atom is 42.57MHz/T T • The strength of magnetic field is measured in gauss T • The Larmor frequency is defined as SUM of the magnetic field and gyromagnetic ratio. F • An MR active nucleus spins at its own precessional frequency. T • ONLY hydrogen nuclei are said to be MR active  F
  18. 18. IN A NUT SHELL
  19. 19. Now, its time to listen to radio in RESONANCE. ►Pushing a swing in time with natural interval of the swing will make the swing higher and higher. ►Similarly, radio frequency pulses in resonance push the aligned protons (H+) to a higher energy level.
  20. 20. WATS RESONANCE???? Def: Energy transition that occur when object is subjected to frequency the same as its own. Here; Radio Frequency "RF" Same Frequency of H nuclei At 90 degree to B0
  21. 21. 2 things happen at Resonance: 1- Energy Absorption Increase number of High energy Spin Up nuclei 2- Phase Coherence NMV precesses in transverse plane at Larmor Frequency
  22. 22. • Energy Absorption: –The MRI machine applies radio frequency (RF) pulse that is specific to hydrogen. –The RF pulses are applied through a coil that is specific to the part of the body being scanned.
  23. 23. MR Signal • NMV rotates around transverse plane. It passes across Receiver Coil inducing voltage in it. • RF Removed  Signal decreased  Amplitude of MR Signal decreased • Free Induction Decay "FID": – Free (No RF Pulse) – ID (because of Decay of Induced signal in Receiver Coil)
  24. 24. SUMMARY TILL NOW…..ENJOYY…
  25. 25. Measuring the MR Signal: – the moving proton vector induces a signal in the RF antenna Measuring the MR Signal z – The signal is picked up by a coil and sent to the computer system. the received signal is sinusoidal in nature – The computer receives mathematical data, which is converted through the use of a Fourier transform into an image. RF signal from precessing protons y x RF antenna
  26. 26. Now, we re-transmit the energy for image processing ►The emitted energy is too small (despite 2500 times the magnetic field with resonance RF pulse) to convert them into images. ►Hence, repeated “ON-OFF” of RF pulses are required. ►The emitted energy is stored (Kspace), analysed and converted into images.
  27. 27. • Imaging: – When the RF pulse is turned off the hydrogen protons slowly return to their natural alignment within the magnetic field and release their excess stored energy. This is known as relaxation. • What happens to the released energy? – Released as heat OR – Exchanged and absorbed by other protons OR – Released as Radio Waves.
  28. 28. The Image
  29. 29. Relaxation Process 1-NMV recovers and realign to B0 this process called "T1 Recovery" 2-Nuclei loose Precessional coherence or dephase and NMV decay in the transverse plane this process called "T2 Decay"
  30. 30. T1 time & T2 Decay are an intrinsic contrast parameter that are inherent to tissue being imaged. T1WI
  31. 31. Definitions Echo Time "TE" Time between RF excitation pulse and collection of signal (it affects the length of relaxation period after removal of RF excitation pulse and the peak of signal received in receiver coil)
  32. 32. • Repetition Time "TR" Time from application of one RF pulse To the application of the next (it affects the length of relaxation period after application of one RF excitation pulse to the beginning of the next).
  33. 33. Flip Angle Angle throw which the NMV moved as result of a RF excitation pulse
  34. 34. Parameters Image contrast controlled by: 1- Extrinsic Contrast parameters: TR, TE & Flip Angle 2- Intrinsic Contrast parameters: T1 Recovery, T2 Decay, Proton Density, Flow & Apparent Diffusion Coefficient
  35. 35. T1 Recovery T1 Recovery Caused by exchange of energy from nuclei to their surrounding environment or lattice "Spin Lattice Energy Transfer" and realign in B0 this occur in exponential process at different rates in different tissue NB: Molecules are constantly in motion; Rotational and Transitional
  36. 36. T1 Recovery T1 in Fat T1 in Water absorb energy quickly T1 is very short i.e. nuclei dispose their energy to surrounding fat tissue and return to B0 in very short time inefficient at receiving energy T1 is longer i.e. nuclei take a lot longer to dispose energy to surrounding water tissue FAT WATER
  37. 37. T1 Recovery Short TR T1 contrast (T1 • TR 300-600 ms • TE 10-30 ms Weighted)
  38. 38. T2 Decay Fat much better at energy exchange than Water Because T2 depends on: 1-How closely molecular motion of atoms matches Larmor Frequency 2-Proximity of other spins So; Fat's T2 time is very short compared to water FAT WATER
  39. 39. T2 Decay Long TE T2 contrast (T2 Weighted) • TR 2000 ms • TE 70 ms
  40. 40. T2* DECAY • T2* relaxation – Disturbances in magnetic field (magnetic susceptibility) increase the rate of spin coherence T2 relaxation • The total NMR signal is a combination of the total number of nuclei (proton density), reduced by the T1, T2, and T2* relaxation components
  41. 41. Proton Density • Proton Density Long TR Proton density • TR 2000 ms • TE 10-30 ms
  42. 42. Gradient Magnets • Used to vary magnetic field in known manner • Each point has slightly different rate of precession & Larmor Frequency. • Variety of signal released by Protons returning to z-plane can used to determine the composition of exact location of each point. • function of "Gradient Magnets” – Slice selection – Frequency encoding – Phase encoding
  43. 43. BRAIN STIMULATOR REGARDING MRI…… • T1 Recovery is due to interactions of intrinsic magnetic fields of adjacent nuclei. • T2 Decay is due to dephasing caused by inhomogenities of external magnetic field. • Fat has short T1 Recovery time. • Water has a short T1 Recovery time. • On T1 fat appears as high signal.
  44. 44. ANSWERS • T1 Recovery is due to interactions of intrinsic magnetic fields of adjacent nuclei F • T2*Decay is due to dephasing caused by inhomogenities of external magnetic fieldT • Fat has short T1 Recovery time T • Water has a short T1 Recovery time F • On T1 fat appears as high signal T
  45. 45. IMAGE QUALITY • Factors that determine image quality Signal: noise ratio , Contrast , Spatial Resolution, Scan time.
  46. 46. SIGNAL : NOISE RATIO • Noise is a random variation in the MR signal, occurring at all frequencies and all the time, due to -1. PATIENT(white noise) 2.ENVIRONMENT. 3. SCANNER. • All noise reduces and obscures contrast bbetween tissues and is worst in areas of low PD and low signal.
  47. 47. IMPROVE SNR… • INCREASING THE SIGNAL BY • INCREASING THE VOXEL SIZE • DECREASING TE AND INCREASING TR/FLIP ANGLE. • SE SEQUENCES > GRE • HIGH TESLA MACHINE • REDUCING NOISE BY • INCREASING THE NUMBNER OF EXCITATIONS • REDUCING BANDWIDTH • REDUCING CROSS TALK
  48. 48. The great headache—ARTIFACTS!! • Image Artifact is something observed in a scientific investigation that is not naturally present but occurs as a result of the investigative procedure. • A structure not normally present, but visible as a result of malfunction in the hardware or software of the device, or a consequence of environmental influences as heat or humidity or can be caused by the human body itself.
  49. 49. WHICH ARTIFACT????
  50. 50. Motion artifacts( ghost)
  51. 51. SPECIAL THANKS TO…….

×