MRI‐visible liquid crystal thermometer

Abstract

Purpose: MRI parameters, such as T 1 , T 2 , and ADC, of tissue-mimicking materials in MRI phantoms can exhibit temperature dependence, and bore temperatures can vary over a 10°C range across different MRI systems. If this variation is not accurately corrected for, the quantitative nature of reference or phantom measurements is irrelevant. Available thermometers require opening the phantoms to probe the temperature, which can introduce contaminants that may affect the stability and accuracy of the phantom. An integrated, MRI-visible thermometer that can be read using typical imaging protocols is needed. Theory and Methods: An MRI-compatible thermometer was designed using liquid crystals (LCs) that exhibit rapid transitions between the LC cholesteric state and isotropic state in the room temperature range spanning 17°C to 23°C in 1.0°C increments. The LC thermometer was assessed visually and using superconducting quantum interference device magnetometry, NMR, and MRI techniques. Results: The signal generated from the LC thermometer was visible with spin-echo and gradient-echo MRI images. The LC state transition temperatures were visually referenced to a National Institute of Standards and Technology-traceable thermometer, and these LC state transitions were confirmed using superconducting quantum interference device magnetometry and NMR. Conclusions: The LC MR-visible thermometer had measurable changes in relative signal with temperature, which were invariant to a variety of imaging sequences used.

A standard system phantom for magnetic resonance imaging

“…Furthermore, the temperature information is not easily encoded in the DICOM files. This establishes the need for in‐situ NMR thermometers, and an MRI‐readable liquid crystal thermometer has been developed for MRI phantoms 35,36 . Furthermore, the system phantom would greatly benefit from the use of materials that are less sensitive to variations in temperature and magnetic field strength.…”

“…This establishes the need for in-situ NMR thermometers, and an MRI-readable liquid crystal thermometer has been developed for MRI phantoms. 35,36 Furthermore, the system phantom would greatly benefit from the use of materials that are less sensitive to variations in temperature and magnetic field strength. Most paramagnetic salts such as MnCl 2 and CuSO 4 have considerable temperature 10 and field dependence (see Supporting Information Figures S10 and S11) in their relaxivity values r 1 , r 2 (mM −1 s −1 ).…”

Technical note: Temperature and concentration dependence of water diffusion in polyvinylpyrrolidone solutions

“…Quantitative Imaging Biomarker Alliance (QIBA) metrology guidelines recommend that systematic bias characterization is performed using phantoms with known ADC values 6,9 . Since water mobility is dependent on temperature, knowledge and control of temperature of diffusing media in phantoms are essential in the course of absolute measurements used for technical QC 10,11 . While temperature dependence of ADC is typically not relevant in living tissue due to body temperature regulation, precise knowledge of temperature and water diffusion within polyvinylpyrrolidone (PVP) materials is a prerequisite for calibration of PVP‐based DWI phantoms prior to their use in assessment of MRI scanner ADC bias and linearity.…”

Temperature‐corrected proton density fat fraction estimation using chemical shift‐encoded MRI in phantoms

“…While it is possible to measure the temperature of the object with a standard thermometer or heat/cool the phantom to the modeled temperature in order to correct the spectral model, this approach may be impractical in many circumstances, and requires operator input, potentially leading to further errors. Other techniques to measure the temperature of the object such as using MR‐visible liquid crystal thermometers 27 or MR thermometry 32 are possible if the operator has access to this thermometer/protocol. It is also possible to create a temperature map of the phantom by including a free parameter temperature term in the spectral model.…”

“…However, measuring the temperature during an acquisition is often impractical, requires human intervention, and assumes that the measured temperature represents the actual temperature throughout the phantom and throughout the imaging experiment. Temperature can be measured using an MR‐visible thermometer such as that developed by Keenan et al 27 instead, but only if this thermometer is available at the time of imaging.…”