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Biotech / Medical : Caprius(CAPR), Breast MRI(former ANMR/MAMO)

CAPR 5.620

-2.6%

Nov 14 9:30 AM EST

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To: James L. Fleckenstein who wrote (2128)	11/11/1997 10:51:00 PM
From: luis a. garcia	Read Replies (1) of 2615

Dc Fleckenstein its time you suffer me through this patent.. Part 1 Background Fat Suppression 5627469. The invention relates to MRI and data processing. MRI generally involves subjecting an object to a magnetic field exciting nuclei in the object using an Rf signal and using the RF resonance signals emitted by the exited nuclei to generate an image of the object or region. Whe excited a nucleous at a point xyz resonates at a resonant frequency that depends on the STRENGTH (as in function of) of the local magnetic field. B(xyz). F(xyz)=Gamma * Beta (xyz) Gamma the gyromagnetic ratio is constant for a particular element in a compound. Because the abundance of Water in the human body. Medical MRI typically images using Hydrogen nuclei in water which have a gyromagnetic ratio of 4.258 KHz/Gauss (42.58 MHz/T) Thus in a 0.5T magnetic field the resonant frequency of Hydrogen nuclei in Water is ~21.3 MHZ. Certain regions of tissue such as female breast include relatively large volumes of intermixed fat and water. For a magnetic field of a given strength the resonant frequency of a hydrogen nucleous in Fat is 3.5 ppm (parts per million) less than the resonant frequency of hydrogen nucleous in water. Thus a fat hydrogen nucleous in a 0.5T field resonates at a frequency that is 74.5 Hz lower than the resonant frequency of a water hydrogen nucleous. That is one small difference 74.5 Hz in 21.3 MHz... Key is Hz (FREQUENCY) difference is very smalllllll.... A typical MRI system generates a magnetic field that varies in STRENGTH both SPATIALLY and TEMPORALLY. The resonant frequency of a particularly exited nucleous therefore DEPENDS on the location of that nucleous within the object being imaged. The MRI system exploits this dependancy between resonant frequency and position to reconstruct the image from the received Rf signal emitted by the excited model. SUMMARY OF THE INVENTION... One aspect of the invention concerns a method and apparatus for generating a magnetic resonance image of a region comprised of two species of nuclei that have non-identical resonant frequencies. After the nuclei are excited TWO gradient pulses are generated. The relative phase offset between the two species of nuclei is different at the center of the first pulse than at the center of the second pulse. Data aquired between the two read out pulses are processed in accordance with these relative phase offsets between the two species, the data collected during the pulses can be processed to generate two images. One image depicts distribution of water and the other fat. IN addition both read out gradients are generated after the same RF excitation pulse. Shortening the period required and preventing shift in the tissues. The relative phase offset at the first read out gradient is 0. the relative phase offset at the second read out gradient is 180 deg. then a third gradient is generated after the other two. The relative phase offset of this third pulse that occurs after 2T center of the first read out is 0. Data collected here is used to correct for phase shifts attributable to inhomogeneities in the main magnetic field. Signals are stored in three matrices during the read out pulses. The aquired RI resonant signals are then processed to generate a magnetic resonance image. Prior to Fourier transforming the thre RI resonant signals to generate images the DC bias is removed from the raw data and some data is time reversed. After Fourier transformation the MAGNITUDE and PHASE of the image data are corrected. Magnitude correction compensates for the exponential T2 magnitude decay.(read out pulse) Phase correction compensates for phase errors attributable to: an echo center that does not lie in the center of the raw data matrix. Inhomogeneities in the static magnetic field and system timing related imperfections. That's it in a nutty shell... at .5T you get 3.5 parts per million or 75 Hz resonance difference between water and fat to work with... at 1T you get 150 Hz and at 1.5T you get a whopping 225 Hz to differentiate with.... big deal still 10.5 ppm We will find out later on as it turns out that the technique will then involve some sort of SUBTRACTION that is the only way in hell we can get those 75 Hz out of that mess.. allright inverting and adding is another way of saying SUBTRACTION SUBTRACTION that's it SUBTRACTION in one pass vs SUBTRACTION in a sequence.. patient twitchens you Hit her over the head with a stick.. right? Yeah they don't show tht in the brochures... The technologist was right? homogeneity is more important than field strength.. ASSUMING YOU PICK UP ENOUGH SIGNAL RIGHT? because its all about SUBTRACTION.... There is more much more.... but these are the basics... it gets deep in a hurry...we will wear boots next time. luis

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