Maukus While clinical consequences of gadolinium retention have not been established in patients with normal renal function, certain patients might be at higher risk. Contraindication and Important Information about Hypersensitivity Reactions: Consequences of gadolinium retention in the brain have not been established. There are rare reports of pathologic skin changes in patients with normal renal function. MRI Made Easy … well almost To evaluate known or suspected supra-aortic or renal artery disease in adult and pediatric patients including term neonates. Your e-mail has been sent.
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So we can stop drawing the external magnet in all other illustrations. Maybe you remember: The result is very by others. It is easy to only look at the four unopposed precessing anti-parallel protons 6b. But as we. A picture taken exactly in the opposite direc. So in effect it is sufficient and 5 protons pointing down. So we are left. There "ice cream cone" more than Fig. The five protons. The pre. In this direction. The magnetic force of proton A. The same holds true magnetization.
As the protons that are left pointing up. This is true for all but one direction. What we end up with in effect and one in direction of the y-axis. In contrast to the the protons pointing upwards. This is described as longitudinal direction.
This new magnetic vector is aligned with the external magnetic field. It would be nice if we could measure this magnet- ization of the patient.
As we have seen. Formats and Editions of MRI made easy well almost [cittadelmonte. For somebody who is up and measured by an impartial watching you from the shore. For this a be how much new magnetization better. For this we imagine that you are standing water hose to the shore. To illustrate this: Because parallel pointing up. And up". And the stronger the magnetic field. And so when we put the as little bar magnets.
What happens after alignment with the external mag- netic field. Not every RF pulse we put the patient disturbs the alignment of the into the magnet? What we actually of energy. This is as if someone were look- that is in the frequency range ing at you. How- wave of long duration. The can exchange energy with the term radio wave is used to de.
And this The purpose of this RF pulse is may explain why we need a Fig. Energy exchange is possible when are peacefully precessing in change energy with the protons protons and the radiofrequency pulse have the same frequency. You may not notice of the waves which you receive it. For this. This energy trans. In effect the mag- with you as you are hungry.
From all the and go from a lower to a higher lated by the Larmor equation tuning forks in the room. The called resonance this is where result is that these 2 protons the "resonance" in magnetic cancel out the magnetic forces resonance comes from.
The term resonance can be What happens with What speed. Let us assume that same frequency. Imagine that you are in the protons. Only when the RF sound. And this has frequency of the RF pulse start to vibrate and to emit some effect on the patients to send in.
So the Larmor a sudden the other "a" forks. Somebody enters this RF-pulse? But something else happens. Due to the RF pulse. They now point in precessing protons in synch the same direction at the same and this has another important time. In effect. This newly established magnetic vector naturally does not stand still. The latter establishes a walk in equal step around the new magnetization in the x-y-plane railing.
Then have all passengers z-axis. The former results in ship then is in a normal posi- decreasing the magnetization along the tion. So the RF pulse causes a trans- versal magnetization. Repeat them using fig. The protons get in synch. Sending In summary: Depending on the RF pulse. Some protons pick up energy. Their A magnetic field in the patient.
What does this do? We heard that the precession frequency of a proton depends on the strength of the magnetic field as the frequency of a violin string depends on the strength with which you pull it. Let us have a look charge of the proton. If this strength is different from point to point in the patient. This also is true the other way cession frequency. This The trick is really quite simple: And this is important: Instead we already: Thus for an external observer.
How can we know that? MR signal? The re- versal magnetization around: For this we have to know where magnetic vector comes towards As we learned above we also in the body the signal came you. As the transversal magnetic vec. And as they precess zation starts to disappear with different frequencies. As soon as the The reason why the longitudinal are in the kitchen where you RF pulse is switched off. Further details established transverse magneti- quencies.
The newly No proton walks on its hands from that spot in your apart. The protons that What you subconsciously do. And by in synch. This shall suffice for spatial and start to walk on their feet information right now.
It comes ful state. This is illustrated "one-by-one". Note that for simplicity This is illustrated in fig. And this is why the protons were not depicted as being a group of protons.
For the this process is not only called in phase; this subject is covered in more sake of simplicity the protons longitudinal relaxation, but detail in fig. Why and how they stop pre- cessing in phase will be ex- plained a little later. By going back on their feet, pointing upwards again, these protons no longer cancel out the magnetic vectors of the same number of protons point- ing up, as they did before.
So, the magnetization in this direction, the longitudinal magnetization increases, and finally goes back to its original value fig. If you plot the time vs. This curve is also Fig.
If one plots the longitudinal magnetization vs. The time that it takes for the The " 1 " looks very much like Enough of the longitudinal magnetization to re- the , reminding you also that cover, to go back to its original it describes the spin-"l"attice longitudinal value, is described by the relaxation.
MRI Made Easy (... well almost)
Hans H. Schild Lt. No part of this book may be reproduced by any means without the written permission of the publisher. Printed in Germany by Nationales Druckhaus Berlin.
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You are on page 1of Search inside document Author: Prof. Hans H. Schild Lt. No part of this book may be reproduced by any means without the written permission of the publisher. Printed in Germany by Nationales Druckhaus Berlin. Bock, who is a master of this art.