UPORABNOST GRADIENTA Z NESTABILNIM RADIOSELEKTIVNIM MAGNETENJEM PRI 3T MAGNETNI RESONANCI. (Slovenian)

THE USE OF GRADIENT WITH VARIABLE RATE SELECTIVE EXCITATION IN 3T MAGNETIC RESONANCE IMAGING. (English)

Introduction: A number of solutions can be used to control the impact of specific absorption rate (SAR) in MRI. After repeating the sequences several times, the body of the patient begins to heat, which is reflected by the elevated body temperature; the temperature is higher during the examination than at the end. By using the variable rate selective excitation (VERSE), the energy (heat) received by the body during MRI is evenly distributed throughout the body, in contrast to examinations with the standard pulse sequences where all the energy is concentrated in the investigated area. Purpose: To show the method of the gradient with variable rate selective excitation which is used at the University Medical Centre Maribor. It reduces SAR and increases effectiveness, compared to the method that uses standard pulse sequences and is otherwise used in the MRI of lumbar spine. Methods: The study included 30 patients who were referred to the lumbar spine MRI with the GE Signa Excite HDxt 3T. Standard sequences and RF pulses were used in the first 15 patients, whereas the method of the gradient with variable rate selective excitation was used in the second group. The effectiveness of the latter was demonstrated by measuring the patients’ temperature before, during and after the MRI. We also recorded the SAR values in both methods. Results: The age of the patients was between 9 and 83, their weight was between 59 and 110 kilograms, 70 percent of them were female. In most cases we found strong correlation between the duration of the examination and the increase in body temperature (r < 0.700), which points to their statistically significant correlation (P < 0.001). This fact confirms the hypothesis that the body temperature of a patient increases with the length of the examination and that the VERSE function reduces the energy in the tissue of the investigated part, due to its distribution throughout the body. Discussion and conclusion: By using the VERSE function with the adjusted RF signal, the heat was evenly distributed throughout the patient’s body. We have proven that the software properly detects overheating of the subject in a given pulse sequence. [ABSTRACT FROM AUTHOR]

Uvod: Za obvladovanje vpliva specifične absorpcijske stopnje (SAR) na telo preiskovanca je pri magnetno resonančnih (MR) preiskavah na voljo več rešitev. Po večkratnem ponavljanju sekvenc se začne telo pacienta greti, kar se odraža s povišano telesno temperaturo, ki je med preiskavo večja kot ob njenem zaključku. Z uporabo gradienta z nestabilnim radioselektivnim magnetenjem (VERSE) se energija (toplota), ki jo telo prejme pri MR preiskavi porazdeli enakomerno po vsem teledu, za razliko od preiskav, pri katerih uporabimo standardna pulzna zaporedja, ko vso energijo prejme preiskovani predel. Namen: Namen je prikazati metodo gradienta z nestabilnim radioselektivnim magnetenjem, ki jo uporabljamo v Univerzitetnem kliničnem centru Maribor, s katero zmanjšamo SAR in njeno učinkovitost v primerjavi z metodo standardnih pulznih zaporedij, ki se sicer uporabljajo za MR prikaz ledvenega dela hrbtenice. Metode dela: Izbrali smo 30 pacientov, ki so bili naročeni na MR preiskavo ledvene hrbtenice na aparaturi GE Signa Excite HDxt 3T. Pri prvih 15 pacientih smo uporabili standardna pulzna zaporedja in RF pulze, pri drugih pa metodo gradienta z nestabilnim radioselektivnim magnetenjem. Učinkovitost slednje smo dokazali z merjenjem temperature pacientov pred, med in po magnetno resonančni preiskavi. Med preiskavo smo pri obeh načinih slikanja beležili vrednosti SAR. Rezultati: Starost pacientov je bila od 9 do 83 let, teža med 59 in 110 kg, 70% jih je bilo ženskega spola. Pri smo ugotovili večinoma močno korelacijo med časom trajanja preiskave in povišanjem telesne temperature (r < 0,700), ki sta statistično značilno povezana (p < 0,001). Iz tega lahko zanesljivo potrdimo hipotezo, da se z dolžino časa preiskave povečuje telesna temperatura pacienta, funkcija VERSE pa pripomore k manjši energiji v preiskovanem tkivu, ker se le-ta porazdeli po celotnem organizmu. Razprava in zaključek: Z uporabo funkcije VERSE s pomočjo prilagojenega RFsignala se prejeta toplota porazdeli po vsem telesu. Dokazali smo, da programska oprema aparature pravilno zazna pregrevanje preiskovanca v določenem pulznem zaporedju. [ABSTRACT FROM AUTHOR]

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