Source: Courtesy of Warner Bros
description
Transcript of Source: Courtesy of Warner Bros
![Page 1: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/1.jpg)
Fysisk institutt - Rikshospitalet1
Source: Courtesy of Warner Bros
Science or black magic?
Chap.12 (3) Medical imagingChap.12 (3) Medical imagingsystems: MRIsystems: MRI
![Page 2: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/2.jpg)
Fysisk institutt - Rikshospitalet2
Principles of MRI
![Page 3: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/3.jpg)
Fysisk institutt - Rikshospitalet3
MRI
Source: Biomed resources
![Page 4: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/4.jpg)
Fysisk institutt - Rikshospitalet4
MRI
Source: MT Scott Diagnostic imaging
![Page 5: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/5.jpg)
Fysisk institutt - Rikshospitalet5
A brief recipe of MRI
1. Put the subject into a strong magnetic field
2. Pass radiowaves through the subject
3. Turn of the radiowaves
4. Recieve radiowaves coming back from the subject
5. Convert the measured RF-data to an image
![Page 6: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/6.jpg)
Fysisk institutt - Rikshospitalet6
Elements contributing to a MRI
• The quantitative properties of the nuclear spin
• The radiofrequency (RF) exitation properties
• Relaxationproperties of the tissue
• Magnetic field strength and gradients
• Thte timing of the gradients, RF-pulses and signal detection
![Page 7: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/7.jpg)
Fysisk institutt - Rikshospitalet7
Prerequisites for depicted nucleus
• A nucleus that is to be pictured must have both: – Spin– Charge
Nucleus with even protonnumbers cannot be used because the spin will cancel each other
![Page 8: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/8.jpg)
Fysisk institutt - Rikshospitalet8
Single-proton
• A single proton has a charge on the surface which is sufficient to form a small current-loop and generates a magnetic momentum µ
• The proton has also a mass that creates an angle-moment J due to the spin
![Page 9: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/9.jpg)
Fysisk institutt - Rikshospitalet9
Hydrogenatoms
• The hydrogenatom is the only large element in the body able to be depicted with MRI. (C, O and N have all even numbers in the proton number).
• Hydrogen is everywhere in the body, primarily combined to water
= All MRI are in fact a picture of hydrogen
![Page 10: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/10.jpg)
Fysisk institutt - Rikshospitalet10
Angle momentum
JJ = m = m=m=mvvrr
mm
vv
rr
JJ
![Page 11: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/11.jpg)
Fysisk institutt - Rikshospitalet11
Magnetic momentum
µ
A
I
The magnetic momentum vector µ=IA
![Page 12: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/12.jpg)
Fysisk institutt - Rikshospitalet12
Precession og relaxation
![Page 13: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/13.jpg)
Fysisk institutt - Rikshospitalet13
Vector direction
• The magnetic momentum and the angle momentum vector is aligned to the spin-axis.
µ=γJ
Where γ is the gyromagnetic ratio, constant for a given nucleus
![Page 14: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/14.jpg)
Fysisk institutt - Rikshospitalet14
Proton interaction with magnetism
• Loaded particles spinning is constructing their own little magnetic field.
- Will line up in the same direction as an external magnetic field
Spinning particles with a mass have an angle momentum – The angle momentum works as a gyroscope and counteracts
changes of the spin direction
![Page 15: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/15.jpg)
Fysisk institutt - Rikshospitalet15
• Ref:www.simplyphysics.com
![Page 16: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/16.jpg)
Fysisk institutt - Rikshospitalet16
Larmour frequencyThe energy difference between
the two alignment states depends on the nucleus
E = 2 z Bo
Eh
/2known as Larmor frequency
/2= 42.57 MHz / Tesla for proton= 42.57 MHz / Tesla for proton
Ref: James Voyvodic
![Page 17: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/17.jpg)
Fysisk institutt - Rikshospitalet17
Resonance frequencies of common nuclei
Note: Resonance at 1.5T = Larmor frequency X 1.5
Ref: James Voyvodic
![Page 18: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/18.jpg)
Fysisk institutt - Rikshospitalet18
MRI
X-Ray, CT
Electromagnetic Radiation Energy
![Page 19: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/19.jpg)
Fysisk institutt - Rikshospitalet19
Magnetization• Sum of all contributions from each nucleus• Large magnetic fields create a big magnetization
M • Temperature dependency • To be able to measure the magnetization, we will
have to disturb it • The quantity of energy supplied (durability for the
RF-pulse at the resonance frequency) will decide how far the nuclei will be pushed away from B
![Page 20: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/20.jpg)
Fysisk institutt - Rikshospitalet20
Radiofrequency field• RF fields are used to manipulate the
magnetization for a specific atom in a specific position
• The hydrogen nucleus is tuned to a certain RF-frequecy
• Eksternal RF-waves can be sent into the subject in order to disturb the hydrogen nucleus
• Disturbed hydrogen nuclei will generate RF-signals with the same frequency – which can later be detected
![Page 21: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/21.jpg)
Fysisk institutt - Rikshospitalet21
To record an MRI signal• Needs a receive coil tuned in to the same RF-requency as
the excitasjonscoil
• Measure net magnetization
• The signal oscillates at the resonansfrequency when the net magnetization vector rotates in the room
• Signalamplitude will be weakened when the netto magnetization returns to the B-direction
![Page 22: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/22.jpg)
Fysisk institutt - Rikshospitalet22
![Page 23: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/23.jpg)
Fysisk institutt - Rikshospitalet23
MRI scanner
![Page 24: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/24.jpg)
Fysisk institutt - Rikshospitalet24
• Larmorequation: ω=γB
• Relationship between parallell / antiparallell protones :
Nn/Ne = ehν/kT =1+410-6
represents net magnetization at room temperature and 1 Tesla
Important MRI equations
![Page 25: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/25.jpg)
Fysisk institutt - Rikshospitalet25
T1 recording
![Page 26: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/26.jpg)
Fysisk institutt - Rikshospitalet26
T2 recording
![Page 27: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/27.jpg)
Fysisk institutt - Rikshospitalet27
MR imagesT1 and T2contrast
![Page 28: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/28.jpg)
Fysisk institutt - Rikshospitalet28
3D picture construction
ω = γB
![Page 29: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/29.jpg)
Fysisk institutt - Rikshospitalet29
T1, T2 and proton-density
![Page 30: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/30.jpg)
Fysisk institutt - Rikshospitalet30
Vertical main field
Source: Oulun Yliopisto
![Page 31: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/31.jpg)
Fysisk institutt - Rikshospitalet31
ExtremityMRI
![Page 32: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/32.jpg)
Fysisk institutt - Rikshospitalet32
Interventional MRI
![Page 33: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/33.jpg)
Fysisk institutt - Rikshospitalet33
![Page 34: Source: Courtesy of Warner Bros](https://reader035.fdocuments.us/reader035/viewer/2022062217/56813a2b550346895da210fd/html5/thumbnails/34.jpg)
Fysisk institutt - Rikshospitalet34
Adv/disadv MRIAdv:No harmful radiationSoft tissue imagingHigh resolution images of T1 or T2 preferences
Disadv:Expensive, large installation with superconducting magnets+
+Very strong magnetic fieldClaustrophobicNot for frozen tissue