Magnetic Resonance Tomography

Magnetic resonance tomography is the technically most complex imaging modality in radiology but it also holds the largest diagnostic potential. Many are terrified by the prospect of having to understand the basic principles of magnetic resonance (MR). All of this is completely unnecessary, of course: the thing is in essence nothing but a bicycle dynamo. But let's start at the beginning.

I Working Principle of Ultrasonography

I Working Principle of Ultrasonography

Ultrasonography Bone And Air

Fig.3.5a If an alternating electric current is sent through a piezoelectric crystal, it vibrates with the frequency of the current, producing sound waves of that frequency. In medical ultrasound, typical frequencies vary between 1 and 15 MHz. Ultrasound gel acoustically couples the ultrasound transducer to the body, where the ultrasound waves can then spread. Inside the body the sound is absorbed, scattered, or reflected. Fluid filled (cystic) structures appear dark and show acoustic enhancement behind them. Bone and air appear bright because they absorb and reflect the sound, showing an "acoustic shadow" behind them.

b This is a modern US scanner (by Toshiba Medical Systems). c These are transducers for different purposes.

Fig.3.5a If an alternating electric current is sent through a piezoelectric crystal, it vibrates with the frequency of the current, producing sound waves of that frequency. In medical ultrasound, typical frequencies vary between 1 and 15 MHz. Ultrasound gel acoustically couples the ultrasound transducer to the body, where the ultrasound waves can then spread. Inside the body the sound is absorbed, scattered, or reflected. Fluid filled (cystic) structures appear dark and show acoustic enhancement behind them. Bone and air appear bright because they absorb and reflect the sound, showing an "acoustic shadow" behind them.

b This is a modern US scanner (by Toshiba Medical Systems). c These are transducers for different purposes.

Generation of the MR Signal

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