Prologue to fMRI material science for shams like me.

Introduction to fmri physics for dummies like me l.jpg
1 / 50
0
0
999 days ago, 437 views
PowerPoint PPT Presentation
Prologue to fMRI material science for shams (like me!). Diagram. History of NMR to X-ray to fMRI Material science of protons (1H specifically) Making X-ray pictures From X-ray to fMRI. History of Atomic Attractive Reverberation. NMR = atomic attractive reverberation Felix Square and Edward Purcell

Presentation Transcript

Slide 1

Prologue to fMRI material science for fakers (like me!).

Slide 2

Outline History of NMR to MRI to fMRI Physics of protons (1H specifically) Creating MRI pictures From MRI to fMRI

Slide 3

History of Nuclear Magnetic Resonance NMR = atomic attractive reverberation Felix Block and Edward Purcell 1946: nuclear cores ingest and re-emanate radio recurrence vitality 1952: Nobel prize in material science atomic : properties of cores of molecules attractive : attractive field required reverberation : association between attractive field and radio recurrence Bloch Purcell NMR  MRI Source: Jody Culham's w eb slides

Slide 4

History of fMRI MRI - 1973: Lauterbur recommends NMR could be utilized to frame pictures - 1977: clinical MRI scanner protected - 1977: Mansfield proposes resound planar imaging (EPI) to secure pictures quicker fMRI - 1990: Ogawa watches BOLD impact with T2* blood vessels turned out to be more obvious as blood oxygen diminished - 1991: Belliveau watches first utilitarian pictures utilizing a differentiation operator - 1992: Ogawa & Kwong distribute first practical pictures utilizing BOLD flag Source: Jody Culham's w eb slides

Slide 5

Some terms to know B 0 – this is utilized to mean the principle attractive field – otherwise called longitudinal charge objects set inside B 0 will bit by bit adjust to this field ( longitudinal relaxation ) M 0 – this is utilized to signify the net polarization of a question inside B 0 it is the M 0 which is "tipped" crooked with B 0 to make the MR image – so M 0 is presently measured as transverse polarization RF beat – radio recurrence beat – not to be mistaken for 'full recurrence' to read M 0 it must be tipped twisted with B 0 – this is accomplished by sending a RF beat at certain thunderous frequencies and slopes

Slide 6

Some more terms to know Magnet – the enormous magnet that we allot the Tesla incentive to that makes B 0 Gradient Coil – littler magnets that are utilized to tip the net charge of the subject (M 0 ) askew with B 0 There are really three angle curls orthogonal to each other so that inclinations can be connected in the x, y and z planes RF loop – radio recurrence loop – these are normally get just curls and are utilized to quantify M 0 eventually after the RF beats have been connected. Send/get loops are additionally accessible

Slide 7

Physics of protons. movement of electrically charged particles brings about an attractive drive orthogonal to the bearing of movement protons (atomic constituent of molecule) have a property of precise energy known as turn Angular force (turn) of a proton.

Slide 8

Inside attractive field In "field free" space M Applied Magnetic Field (B 0 ) situated with or against B 0 M = net polarization haphazardly arranged Protons adjusting inside an attractive field when set in an attractive field (B 0 ; e.g., our MRI machines) protons will either adjust to the attractive field or orthogonal to it (procedure of achieving attractive balance) there is a little distinction (10:1 million) in the quantity of protons in the low and high vitality states – with additional in the low state prompting to a net charge (M) Source: Mark Cohen's web slides Source: Robert Cox's web slides Source: Jody Culham's w eb slides

Slide 9

Precession – the turning top relationship. What is really adjusted to the B 0 is the pivot around which the proton precesses – the rot of precession (i.e., it is the rate of precession crooked with B 0 together with the proton thickness of the tissue worried that is vital in MRI) Source: Cohen and Bookheimer article

Slide 10

170.3 Resonance Frequency for 1H 63.8 1.5 4.0 Field Strength (Tesla) Larmor Frequency the vitality distinction between the high (situated with B 0 ) and low (arranged against B 0 ) vitality protons is quantifiable and is communicated in the Larmor condition Larmor condition f = B 0  = 42.58 MHz/T At 1.5T, f = 63.76 MHz At 4T, f = 170.3 MHz

Slide 11

RF Excitation protons can flip amongst low and high vitality states (i.e., flip between being adjusted to or against B 0 ) to do as such the vitality exchange must be of an exact sum and should be encouraged by another drive (e.g., different protons or atoms) in MRI, RF (radio recurrence) heartbeats are utilized to energize the RF field – the Swing relationship – tipping the net polarization twisted with B 0

Slide 12

Cox's Swing Analogy Source: Robert Cox's web slides

Slide 13

B 0 B 1 RF Excitation Excite Radio Frequency (RF) field transmission curl : apply attractive field along B1 (opposite to B 0 ) for ~3 ms swaying field at Larmor recurrence frequencies in scope of radio transmissions B 1 is little: ~1/10,000 T tips M to transverse plane – spirals down analogies: guitar string (Noll), swing (Cox) last edge between B 0 and B 1 is the flip edge Source: Robert Cox's web slides

Slide 14

Longitudinal unwinding and T1. temperature impacts the quantity of crashes (and consequently the rate at which protons flip amongst low and high vitality states) so attractive harmony (M 0 ), or the rate at which a body set inside B 0 gets to be distinctly polarized relies on upon temperature – this is known as longitudinal unwinding the T1-weighted picture (generally utilized for anatomical pictures) measures the rate at which the question set in B 0 (the clueless subject for our situation) goes from a non-charged to a charged state – the longitudinal unwinding diverse sorts of particles (and by augmentation tissue) approach M 0 at various rates permitting us to separate things like white and dark matter – we crawl close towards the picture!!!

Slide 15

T1 and T2 T1 measures the longitudinal unwinding (along B 0 ) – or the rate at which the subject (and the different diverse constituents of that subject) achieves attractive harmony T2 measures the transverse unwinding (along B 1 ) – or the rate of rot of the flag after a RF heartbeat is conveyed T1 – recuperation to condition of attractive balance T2 – rate of rot after excitation Tissue T2 rot times (in 1.5 T magnet) white matter 70 msec dark matter 90 msec CSF 400 msec

Slide 16

Reading M 0 RF curls get the net charge from the question put inside the loop (e.g., a subject's head) can likewise have send/get RF curls that additionally convey the RF heartbeat (to get the swing going) – for the most part the beat is conveyed by slope curls

Slide 17

Proton thickness, recuperation (T1) and rot (T2 and T2*) times. T1 weighted Density weighted T2 weighted By "weighting" the beat grouping (and time when information is gathered) distinctive pictures of the cerebrum are acquired Weighting is accomplished by controlling TE (time to reverberate) and TR (time to redundancy of the beat succession)

Slide 18

all cores adjusted and precessing in a similar bearing. cores not adjusted but rather as yet precessing in a similar course. Precession In and Out of Phase So MR flag will begin off solid yet as protons precess out of stage the flag will rot. Source: Mark Cohen's web slides

Slide 19

T1 and TR T1 = recuperation of longitudinal (B 0 ) charge after the RF beat used in anatomical pictures ~500-1000 msec (longer with greater B 0 ) TR (reiteration time) = time to hold up after excitation before examining T1 Source: Mark Cohen's web slides

Slide 20

T2 and TE T2 = rot of transverse polarization after RF beat TE (time to resound) = time to hold up to quantify T2 or T2* (after re-centering with turn reverberate) Source: Mark Cohen's web slides

Slide 21

T1 and TR T1 versus T2 viably, T1 and T2 pictures are the backwards of each other, with T1 ordinarily used to frame anatomical pictures and T2* utilized as a part of fMRI

Slide 22

T2* T2 : inborn rot of transverse polarization over minuscule area (~5-10 microns) ~50-100 msec (shorter with greater B 0 ) T2*: general rot of transverse charge over naturally visible locale (~mm) rots more rapidly than T2 (by component of ~2) Source: Robert Cox's web slides

Slide 23

T1 versus T2 Source: Mark Cohen's web slides

Slide 24

Repetition and reverberate time reliance. Source: Buxton book Ch. 8

Slide 25

RF beat Gx (x – slope) information procurement time Spatial localisation of the flag – making the 1D picture. A spatially variation B 1 prompts to a spatially variation dissemination of RFs. Recurrence examination is utilized to segregate diverse spatial areas. Beat SEQUENCE

Slide 26

add an angle to the primary attractive field energize just frequencies relating to cut plane Freq Field Strength (T) ~ z position Gradient curl Spatial Coding Gradient attractive field = connected in the cut plane (i.e., the x bearing) in this way Gx

Slide 27

Spatial localisation of the flag – making the 2D picture. Can't just turn on 2 inclinations. Rather the 2 angles require an exact succession. The 1D grouping as of now demonstrated is known as recurrence encoding . An alternate heartbeat arrangement can be utilized as a part of the y-course to make the 2D picture – stage encoding . This strategy is known as resound planar imaging or EPI and is the most well-known technique utilized as a part of fMRI.

Slide 28

Spatial localisation of the flag – making the 3D picture The RF field must be at an indistinguishable thunderous recurrence from the core being filtered. For the 2D picture we have chosen just a single thunderous recurrence in one specific z-plane (and utilized EPI to groupings to get the x and y-planes). So we just apply an inclination at various levels (cuts) in the z-plane to make the 3D picture. cuts in the z-plane

Slide 29

Spatial localisation of the flag – making the 3D picture frequ. encode stage encode Source: Buxton book Ch. 10

Slide 30

Echos All RF beats make a "reverberate" of the M 0 flag got by the beat. T2* signals rot more quickly than T2 A refocusing heartbeat is utilized to make a transient resound of the

SPONSORS