Help with Med Phys - appreciate it :) (1 Viewer)

~TeLEpAtHeTiC~

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ok guys
i was orginally doing geophysics
but due to NO resources what so ever
and an apathetic teacher
last night i changed my option to medical physics
only 3 days from exam
well i finished it within 5ish hours
and my notes are good
BUT for the following dot points under the heading
'4. the magnetic field produced by nuclear particles can be used as diagnostic tools'
although i have notes..after typign them up i find them very iffy
can in please get someone elses who rekons theres is comprehensive and has the right answers form the dot points on this page?

i'd appreciate it immensly and the fact that i'm doing it in the last minute, i'd appreciate any help

its sjut all dot points onthat last page..
if you hav any note (ie summarys of dot points) can u please contact me

once again, i'd appreciate it heaps
thanks for any help
goodluck everyone
 

destination

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dude
post ur syllabus dot points that u dont understand...
i'll give u sum points i had for the syllabus
 

antdude20

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here are mine for that part of med


The magnetic Field produced by nuclear particles can be used as a diagnostic tool

*-Identify that the nuclei of certain atoms and molecules behave as small magnets-

If the wire (current carrying wire) is a circle (a current loop), the field produced is similar to that of a simple bar magnet, with a north and a south pole.

A charged particle, such as a proton or electron, acts like a tiny current loop. So too, the nuclei of atoms and molecules behave as small magnets.

This phenomenon is related to the spin of the charge.




*-Identify that protons and neutrons in the nucleus have properties of spin and describe how net spin is obtained-


Spin is a measure of the intrinsic angular momentum of any elementary particle.

Both protons and neutrons in an atomic nucleus have a property referred to as spin, each spinning on its own axis (axial spin) and also spinning about the central axis of the nucleus (orbital spin).

Directions of spin for any pair of protons or any pair of neutrons are opposite and are distinguished from each other by referring to them as spin up (+) or spin down (-).

The resultant or net spin of a nucleus is a combination of both axial and orbital spin of each of the nucleons in the atomic nucleus of an atom. Net nucleus spin is measured in S (quantum number) units with + indicating spin up and - indicating spin down.

*-Explain that the behavior of nuclei with a net spin, particularly hydrogen, is related to the magnetic field they produce-


A spinning charged particle has associated with it a magnetic field. It therefore followed that any atomic nucleus with net spin that contains protons has a magnetic field associate with it and can be considered to be a small magnet with a north and South Pole. The hydrogen proton in particular, S=1/2, has two energy states, -1/2 and +1/2. This means that hydrogen protons are spinning about their axis and creating a magnetic field. Some hydrogen protons spin one way, and some spin the opposite way and have a magnetic field in opposite direction.

*-Describe the changes that occur in the orientation of the magnetic axis of nuclei before and after the application of a strong magnetic field-


When a bar magnet is placed in an external magnetic field it attempts to align itself with that field. This is the phenomenon on which a magnetic compass relies for its operation.

Similarly this applies to spinning hydrogen protons. They try to align them selves with the field. However due to quantum mechanics they are restricted in their alignment and must remain in one of two specific orientations of angles to the field. These two allowable orientations are referred to as spin up (parallel lower energy state) and spin down (anti-parallel higher energy state).

*-Define precessing and relate the frequency of the precessing to the composition of the nuclei and the strength of the applied external magnetic field-


When set spinning about one axis V the axis of symmetry V the top will also rotate around the second axis. This change in direction of the original axis of rotation is called precession.

The rate or frequency at which the nucleus precess is related to both the composition of the nucleus and the strength of the external magnetic field and is unique to each atomic nucleus. That is different nuclei have different precessional frequencies for a specific magnetic field strengths.

For a specific atomic nuclei the precessional frequency is proportional to the external magnetic field strength.

The precessional frequency of a nuclei is called the Larmor frequency and is related to the energy difference between the lower energy parallel and higher energy anti parallel states.

The uniqueness of the Larmor frequency or precessional frequency of specific atomic nuclei that enables MRI to identify and distinguish body tissue with differing chemical makeups.

*-Discuss the effect of subjecting precessing nuclei to pulses of radio waves-


If a human being is placed in an external magnetic field, the spinning unpaired protons within the body will line up with the external magnetic field. If a specific radio frequency is then sent into the patient, some spins will change their alignment as a result of this new magnetic field. After the RF pulse, the protons return to their original alignment. This signal is the magnetic resonance frequency received back from the patient, and which is measured and recorded in MRI.

*-Explain that the amplitude of the signal given out when precessing nuclei relax is related to the number of nuclei present-


All relaxing nuclei release excess energy as radio wave radiation with an identical Larmor frequency. However the greater the number of relaxing hydrogen nuclei the greater the amplitude or intensity of the radio wave radiation emitted. By measuring the time taken for the initial intensity of the radiation to drop to 63% it is possible to determine the proton density of the sample.

*-Explain that large differences would occur in the relaxation time between tissue containing hydrogen bound water molecules and tissues containing other molecules-


Because of the exponential relaxation the amplitude of the re-radiated Larmor frequency radiation also decreases exponentially. From this the proton density can be calculated.

If a tissue sample contains only water molecules then its proton density will be very high due to high proportion of hydrogen atoms.

If a tissue under test contains other molecules then the time for relaxation is much shorter.


....cudnt upload it something wrong wif uploading in the forum for me atm
 

~TeLEpAtHeTiC~

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thanx antedude that exactly what i was after
after reading through like 2 textboks on that section i was still rather confused in my head... heh.. os much easier to get a 'laymans' interpretation of the bull shit.. thanx mate appreciate it heaps..
if anyone else has their own interpretation of the above dot points can u post to plz?
thanx again
 

freaking_out

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Originally posted by ~TeLEpAtHeTiC~
ok guys
i was orginally doing geophysics
but due to NO resources what so ever
and an apathetic teacher
last night i changed my option to medical physics
only 3 days from exam
well i finished it within 5ish hours
and my notes are good...
ur one brave kid. :D
 

Inhuman

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Here are some websites which my teacher gave us about MRI.The first one is pretty good (and cool-looking too!)

MRI animation on how it works
http://www.simplyphysics.com/IntroToMRI.html
http://www.technologyreview.com/articles/visualize0701.asp
http://www.cis.rit.edu/htbooks/mri/inside.htm

http://www.cis.rit.edu/htbooks/mri/

Images for functional MRI
http://www.fmrib.ox.ac.uk/image_gallery/

MRI and acupuncture points
http://www.reflexology-research.com/mri.htm

As for my interpretation... what the heck, it can only help me to explain it to someone else:

The Identify dot points: fairly self-explanatory. You don't really need more detail than what's already written

Describe how net spin is obtained:
every nuclear particle spins on own axis. Nuclear particles can be either spin up or spin down.
The combination of the spin of protons and neutrons gives net spin. there are rules for whether the nucleus will have 0,integer or fractional spin depending on the nymber of protons and neurons present but they're not important. The hydrogen atom has a spin of +/- 1/2

Explain that the behaviour of nuclei with a net spin, esp hydrogen is related to the magnetic field they produce:
A moving charge creates a magnetics field(M+G) NB:In a diagram the direction of the magnetic field of the nucleus is related to the direction of spin by the solenoid rule

descirbe the changes that occur in the orientation of the magnetic axis of nuclei before and after the application of B

Normally the orientation of the nuclei is random. When a magnetic field is applied they line up either in the same direction as the magnetic field(parallel) or opposite(anti-parallel). When the external field is removed they slowly reurn to random orientation

define precessing
this is when the nucleus spins not only on it's own axis but around a central axis
and relate the freq of precessing to the composition of the nuclei and the strength of the external field
the freq is directly proportional to the external field strength and is defined by the Larmour equation. The freq is also determined by the composition of the nucleus because hydrogen is greatly affected due to having only one proton and no neutrons.

discuss the effect of subjecting precessing nuclei to pulses of radio waves
parallel and anti-parallel do not have the same energy. Parallel nuclei are at a slightly lower enrgy state so a few more per billion are parallel than anti-parallel. The larmour freq for hydrogen atoms happens to be the same freq as radio waves. When the nuclei are subjected to radio waves it gives some parallel nuclei enough energy to flip to anti-parallel. after the radio pulse is over the nuclei will return to parallel, emitting the extra energy which we detect to form images

explain that the amp of the signal given out is related to the no of nuclei present
seems fairly self-exlanatory to me... the more nuclei the more EM waves emitted, the waves super-position to create a signal with higher amp. As Antdude said the time taken for the intensity to drop to 63% is used to measure proton density and is known as T1 and lasts about a second

explain the large differences occurring in relaxation time between various tissues
the hydrogen acts differently depending on how free it is to respond to the RF signal. In water its only loosely bound, in fat and stuff its more tightly bound. The relaxation time is much faster in muscle than fat and in fat than it is in water


Some miscellaneous info not fitting into above points:
*Hydrogen is targeted because it has greatest response and because it's so common everywhere.
*Slice of the body are taken by using a gradient magnetic field and a horizontal one, which means that the Larmour freq will differ slightly depending on which part of the body you want to image
*images look different depending on whether they are weighted towards T1 or T2 relaxation. T2 is the process by which the protons go out of phase with eachother and lasts about 50ms
 
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Hey just wondering y are u only just changing ur topic now just days from the exam?
 

Jago

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1st post - Old 28th October 2003, 06:42 AM
 

SOMMAIA

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help plzzzzzzzzzzz

hi

i am in da same position as u
just woundering if u could send me the notes on med. phy to me tooo
use
i have forgetton everything since the trial and cant seem to get around it anymore

its better then nothing :rolleyes:

plzzzzzzzzzzzzzzzzzzzzzzzzzz

thanks :confused:

bye

if u dont mind send it to
queensommaia@yahoo.com

thanx again
 

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