Kolmiulotteinen lämpötilamittaus protoniresonanssin avulla

Proton resonance frequency (PRF), by which it precesses in the magnetic field, alters due to change in temperature, which can be detected with magnetic resonance imaging (MRI). MRI scanner uses protons’ nuclear magnetic resonance phenomenon. The target is first excited with a radio frequency pulse, then its relaxation to initial stage is observed. Parts with different temperatures can be mapped according to the characteristics of the signal they emit during relaxation. PRF thermometry is recognized as the best method to study in vivo temperature distribution with MRI scanner. PRF thermometry is favored due to a good large scale linearity and tissue independence. When tissue containing water is heated, the hydrogen bonds between water molecules are soften as a result of increased Brownian motion. When hydrogen bonds are weaker, the magnetic shielding from electron cloud around proton is stronger. Now that the magnetic shielding is stronger, the local magnetic field of that proton is weakened. Lower magnetic field leads to lower proton nuclear magnetic resonance. Change in nuclear magnetic resonance can be detected with phase difference mapping as a phase shift in phase images with MRI scanner. Noninvasiveness is universally justified in clinical medicine. Diseases and tumors in living tissues can be noninvasively treated with hyper- or hypothermia. Abnormal situations can be detected by observing the temperature changes in the body. MRI scanner can be used to examine tissue temperatures during temperature treatments. Temperature mapping can also be used to monitor unwanted tissue heating related to MRI examinations. The purpose of this thesis is to produce volumetric thermometry data with proton resonance, and to optimize the imaging parameters in order to achieve the best signal-to-noise ratio for magnetic resonance thermometry.Protonin resonanssitaajuus (PRF), jolla se prekessoi magneettikentässä, muuttuu lämpötilan muutoksen johdosta, joka voidaan nähdä magneettikuvauslaitteen avulla. Magneettikuvauslaite käyttää hyväkseen protonien ydinmagneettista ilmiötä. Kohdetta viritetään ensin radiotaajuuspulssilla, jonka jälkeen seurataan sen palautumista alkutilaan. Eri lämpöiset alueet kohteessa voidaan kartoittaa niiden lähettämän eri taajuisen signaalin avulla palautumisen aikana. PRF muutos on tunnustettu parhaaksi menetelmäksi seurattaessa elävien kudosten sisäisiä lämpötilaeroja magneettikuvauslaitteen avulla. Etuna PRF menetelmässä toisiin magneettikuvauksen avulla tehtäviin lämpömittausmenetelmiin on sen hyvä lineaarisuus laajalla mittausalueella, ja riippumattomuus kudostyypistä. Kun vettä sisältävä kudos lämpenee, siinä olevien vesimolekyylien väliset vetysidokset heikkenevät lisääntyvän lämpöliikkeen vuoksi. Kun vetysidokset heikkenevät, kasvaa veden protonien ympärillä olevien elektronipilvien magneettinen suojaus. Kun magneettinen suojaus kasvaa, kokee protoni magneettikuvauslaitteen magneettikentän paikallisesti heikompana. Kun paikallisesti koettu magneettikenttä on heikompi, on myös protonin resonanssitaajuus pienempi. Tämä havaitaan magneettikuvauslaitteen vaihekuvissa vaihe-erona. Vaihemuutoskartan avulla voidaan kartoittaa kohteen lämpötilaeroja. Minimaalinen kajoamattomuus on yleisesti perusteltua lääketieteellisissä hoidoissa. Kehon lämpötilamuutosten avulla saadaan tietoa kehon anomaalisista tiloista. Elävissä kudoksissa olevia tauteja ja kasvaimia voidaan hoitaa kajoamattomasti lämpö- ja kylmäterapialla. Magneettikuvauslaitteella voidaan seurata kudosten lämpötilaa hoitojen aikana, sekä kartoittaa kehon poikkeavia lämpötilaeroja. Vaihekartoituksen avulla voidaan seurata myös magneettikuvaukseen liittyvää kudosten lämpenemistä. Tämän työn tavoitteena on muodostaa lämpötilatietoa kuvaava tilavuuskartta protonin resonanssitaajuuteen perustuvalla menetelmällä, ja optimoida kuvausparametrejä parhaan signaalikohinasuhteen saavuttamiseksi lämpötilamittauksen osalta

MRI for Noninvasive Thermometry

MRI was recognized for its potential use as a noninvasive in vivo thermometer 30 years ago. Today, the most popular application of MR thermometry is the guidance of thermal therapies for the treatment of cancer and other pathologies. These minimally invasive operations are routinely performed on patients who are not eligible for surgery in approximately 40 medical centers globally. The aim is to deliver or abduct thermal energy in order to cause local tissue necrosis or to sensitize a lesion to chemotherapy or radiotherapy without causing harm to the surrounding healthy tissue. Here we explain the principles of operation of MR thermometry and provide a critical review of the proposed methods, highlighting remaining fundamental and technical issues as well as recent progress. Emphasis is placed on hardware advances (RF receivers) for improved signal-to-noise ratio (SNR) which would lead to better accuracy, spatiotemporal resolution, and precise calibration. We conclude with a general outlook for the field

Clinical performance and future potential of magnetic resonance thermometry in hyperthermia

Hyperthermia treatments in the clinic rely on accurate temperature measurements to guide treatments and evaluate clinical outcome. Currently, magnetic resonance thermometry (MRT) is the only clinical option to non-invasively measure 3D temperature distributions. In this review, we evaluate the status quo and emerging approaches in this evolving technology for replacing conventional dosimetry based on intraluminal or invasively placed probes. First, we define standard-ized MRT performance thresholds, aiming at facilitating transparency in this field when comparing MR temperature mapping performance for the various scenarios that hyperthermia is currently applied in the clinic. This is based upon our clinical experience of treating nearly 4000 patients with superficial and deep hyperthermia. Second, we perform a systematic literature review, assessing MRT performance in (I) clinical and (II) pre-clinical papers. From (I) we identify the current clinical status of MRT, including the problems faced and from (II) we extract promising new techniques with the potential to accelerate progress. From (I) we found that the basic requirements for MRT during hyperthermia in the clinic are largely met for regions without motion, for example extremities. In more challenging regions (abdomen and thorax), progress has been stagnating after the clinical introduction of MRT-guided hyperthermia over 20 years ago. One clear difficulty for advancement is that performance is not or not uniformly reported, but also that studies often omit important details regarding their approach. Motion was found to be the common main issue hindering accurate MRT. Based on (II), we reported and highlighted promising developments to tackle the issues resulting from motion (directly or indirectly), including new developments as well as optimization of already existing strategies. Combined, these may have the potential to facilitate improvement in MRT in the form of more stable and reliable measurements via better stability and accuracy