year 4 day 3 syllabus, IV rok, IV rok CM UMK, Radiologia, 2014-15

//-->.pos {position:absolute; z-index: 0; left: 0px; top: 0px;}10/17/2012Day 3RADIOLOGY ANDDIAGNOSTIC IMAGINGDr. Zbigniew Serafin, MD, PhDserafin@cm.umk.plTimeline of MR Imaging1972 – Damadianpatents idea for largeNM R scanner todetect malignanttissue.1985 – Insurancereimbursements forM RI exams begin.1924 - Pauli suggeststhat nuclear particlesmay have angularmomentum (spin).1937 – Rabi measuresmagnetic moment ofnucleus. Coins“magnetic resonance”.1973 – Lauterburpublishes method forgenerating imagesusing NM R gradients.M RI scannersbecome clinicallyprevalent.NM R renamed M RI192019301940195019601959 – Singermeasures blood flowusing NM R (inmice).19701980199020001946 – Purcell showsthat matter absorbsenergy at a resonantfrequency.1973 – M ansfieldindependentlypublishes gradientapproach to M R.1990 – Ogawa andcolleagues createfunctional imagesusing endogenous,blood-oxygenationcontrast.1946 – Bloch demonstratesthat nuclear precession can bemeasured in detector coils.1975 – Ernstdevelops 2D-Fouriertransform for M R.110/17/2012Synopsis of MRI1)Put subject in big magnetic field2)Transmit radio waves into subject[2~10 ms]3)Turn off radio wave transmitter4)Receive radio waves re-transmitted bysubject5)Convert measured RF data to imageWhat kinds of nuclei can be used for MRI?•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 withan odd number of protons or neutrons have spin▫ Good MR nuclei are1H,13C,19F,23Na,31PCommon nuclei with NMR propertiesCriteria:Must have ODD number of protons or ODD number of neutrons.Reason?It is impossible to arrange these nuclei so that a zero net angularmomentum is achieved. Thus, these nuclei will display a magneticmoment and angular momentum necessary for NMR.Examples:1H,13C,19F,23N, and31P with gyromagnetic ratio of 42.58, 10.71,40.08, 11.27 and 17.25 MHz/T.Since hydrogen protons are the most abundant in human body, weuse1H MRI most of the time.210/17/2012Common nuclei with NMR propertiesHydrogen atoms are best for MRI•Biological tissues are predominantly12C,16O,1H, and14N•Hydrogen atom is the only major species that is MR sensitive•Hydrogen is the most abundant atom in the body (63%)•The majority of hydrogen is in water (H2O)•Essentially all MRI is hydrogen (proton) imaging•Some types of tissues prevent hydrogen from spinning asfreely. For example, bone is more restrictive to movementthan fat. These differences can be detected to distinguishtissue type.Angular MomentumJmvJ= mw=mvrrmagnetic momentm= gJwhere g is the gyromagnetic ratio, and it is a constantfor a given nucleus310/17/2012A Single ProtonThere is electricchargeon the surface of theproton, thus creatinga small current loopand generatingmagnetic momentm.mJ+++The proton alsohas mass whichgenerates anangularmomentumJwhen it isspinning.Thus proton “magnet” differs from a magnetic bar in that italso possesses angular momentum caused by spinning.How do protons interact with a magnetic field?•Moving (spinning) charged particle generates itsown little magnetic field▫ Such particles will tend to line up with externalmagnetic field lines (think of iron filingsaround a magnet)•Spinning particles with mass have angularmomentum▫ Angular momentum resists attempts to changethe spin orientation (think of a gyroscope)How do protons interact with a magnetic field?Ref: www.simplyphysics.com410/17/2012Main Magnet FieldBoH protons in H2O behave like little magnetsMain magnet and some of its lines of force[Little magnets lining up with external lines of force]Main Magnet FieldBoProtons in a Magnetic FieldBoParallel(low energy)Anti-Parallel(high energy)Spinning protons in a magnetic field will assume two states.If the temperature is 0oK, all spins will occupy the lowerenergy state.5

zanotowane.pl

doc.pisz.pl

pdf.pisz.pl

kachorra.htw.pl