فكرة عمل جهاز التصوير بالرنين المغناطيسي Mri

[أحلام ضائعة]

يسلمو د/ حازم
و فعلا ما شاء الله عنك موضوع قمة بالاهمية و ان شاء الله السنة الجاى راح يفيدنى و هيكون مرجع الى باذن الله


دمت بخير
جزيت الجنة

[HazemSakeek]

مرحبا بك احلام في المنتدى وشكرا لك على المرور

هذا يعني انك فيزائية طبية

دعواتي لك بالتوفيق

تحياتي

[ماجستير هندسة ليزر]

السلام عليكم ورحمة الله وبركاته

حياكم الله

اعجبني الموضوع

ولكن عى فكرة يجب الفحص اولا قبل الدخول لهذا النوع من الاجهزة حيث لا يسمح لمرضى القلب بالفحص به

شكرا

سلامي

[eman ramadan]

السلام عليكم يادكتور /حازم
شكرا على الموضوع رائع ولدى سؤال لأنى حاليا أقوم ببحث فى MRI
أريد أن أعرف
what is type of FS sequenses and how transform this sequenses into image

[انديرا الحنفي]

شكرا دكتوري العزيز بالاضافه الي كلامك احب ان اقول ان نووي له علاقه يالغزل النووي الذي تقوم به النواه اي ان الطاقه المستخدمه طاقة نوويه .

[Athena]

تم إعــادة ترتيب المواضيع



بالتوفيق



...

[farok]

السلام عليكم يادكتور /حازم
شكرا على الموضوع رائع ولدى سؤال لأنى حاليا أقوم ببحث فى MRI
أريد أن أعرف
what is type of FS sequenses and how transform this sequenses into image

Pulse sequences and RF



Rf pulses are the primary determinant of sequence timing. The sequence timing is initiated (time = zero) at the middle of the excitation pulse for standard rf pulses. For multiple Rf pulse sequences such as double echo or turbo spin echo, all timing is referenced to this point. Rf pulses of amplitude 180 degrees applied prior to the excitation pulse are inversion pulses and are used in Inversion Recovery pulse sequences. 180 degree Rf pulses applied following the excitation pulse are refocusing pulses and reverse the phase of the protons relative to the transmitter phase. Rf pulses have both a center frequency and a range or bandwidth of frequencies. In the presence of a gradient, the center frequency determines the center of the excitation volume, while the bandwidth determines the thickness of the volume. The bandwidth is determined by the width and shape of the pulse or envelope. The pulse shapes are stored in digital form and are combined with the center frequency prior to amplification


Pulse sequences and RF


Four common pulse shapes are:

-Sinc. Sinc functions are used for slice selective excitation. They have relatively sharp edges to the volume of excitation (i.e., they produce good slice profiles). The frequency bandwidth is typically between 500-1500 Hz.


-Gaussian. Gaussian functions are used for frequency selective saturation pulses in the absence of a gradient pulse such as fat saturation or Magnetization Transfer Suppression (MTS). They have very narrow bandwidths for these purposes, typically 50-100 Hz.
-Hyperbolic secant. Hyperbolic secant functions are used for inversion pulses because the necessary RF power is lower than for the corresponding sinc function.


-Nonselective or rectangular. Nonselective pulses excite large frequency ranges (100-200 kHz) with a uniform amplitude, effectively exciting all protons within the field of the transmitter coil.

-While it is the pulse amplitude integral that determines the amount of proton rotation and is limited by the RF transmitter, it is the pulse power integral that is monitored by the SAR monitor to ensure that the patient is not exposed to excessive RF energy.