Temperature‐induced tissue susceptibility changes lead to significant temperature errors in PRFS‐based MR thermometry during thermal interventions

Abstract

Proton resonance frequency shift-based MR thermometry (MRT) is hampered by temporal magnetic field changes. Temporal changes in the magnetic susceptibility distribution lead to nonlocal field changes and are, therefore, a possible source of errors. The magnetic volume susceptibility of tissue is temperature dependent. For water-like tissues, this dependency is in the order of 0.002 ppm/°C. For fat, it is in the same order of magnitude as the temperature dependence of the proton electron screening constant of water (0.01 ppm/°C). For this reason, proton resonance frequency shift-based MR thermometry in fatty tissues, like the human breast, is expected to be prone to errors. We aimed to quantify the influence of the temperature dependence of the susceptibility on proton resonance frequency shift-based MR thermometry. Heating experiments were performed in a controlled phantom set-up to show the impact of temperature-induced susceptibility changes on actual proton resonance frequency shift-based temperature maps. To study the implications for a clinical case, simulations were performed in a 3D breast model. Temperature errors were quantified by computation of magnetic field changes in the glandular tissue, resulting from susceptibility changes in a thermally heated region. The results of the experiments and simulations showed that the temperature-induced susceptibility changes of water and fat lead to significant errors in proton resonance frequency shift-based MR thermometry. Magn Reson Med 64:1360-1372, 2010. V C 2010 Wiley-Liss, Inc. Key words: susceptibility; temperature; PRFS-based MR thermometry; HIFU; fat; glandular tissue Next to excellent soft-tissue contrast, MRI also offers methods to acquire temperature maps, which allow for monitoring and guiding of thermal interventions. Proton resonance frequency shift (PRFS)-based MR thermometry (MRT) is the most commonly used temperature monitoring technique. It is based on the temperature dependence of the proton resonance frequency (PRF) of protons in water molecules and is thus applicable in water-containing tissues. The technique does not work for protons in fat molecules and for this reason adequate fat suppression is essential for accurate thermometry in tissues containing both water and fat.PRFS-based MRT is hampered by temporal field changes. In the application of this technique, the contribution of field changes, which originate from temperature-induced magnetic volume susceptibility changes, is commonly ignored. This disregards the fact that the magnetic volume susceptibility x (which will hereinafter be referred to as ''susceptibility'') of water and water-containing tissue is temperature dependent (1,2). Several studies have suggested that this may lead to PRFS-based temperature errors in water and water-containing tissues (1-4). This has been shown for water (3) and brain tissue (2), which both have a temperature dependent susceptibility in the order of dx/dT ¼ 0.002 ppm/ C.In tissues containing both water and fat, more considerable susceptibility-relat...

Magnetic resonance thermometry: Methodology, pitfalls and practical solutions

“…High fat content tissue consequently hampers temperature reading accuracy. Simulations in breast tissue demonstrated a maximum error of -8.6°C for an absolute temperature change of ∆T=30°C in HIFU ablation (43). Assuming more realistic temperature dependent susceptibilities of fat (63), this would result in a standard deviation of ~1°C for a ∆T=5°C in an hyperthermia application.…”

“…This is a major drawback of the PRF method for accurate MR thermometry in and around fatty tissues (43,62). While the temperature dependent magnetic susceptibility of water based tissue is rather small with ݀߯ ௪௧ /݀ܶ = 0.0016 ‫ܥ°/݉‬ (muscle tissue (42)) as compared to the changes in the electron screening constant, the susceptibility of fat ݀߯ ௧ /݀ܶ = 0.0039 − 0.0076 ‫ܥ°/݉‬ (breast fat (43)) is close to the proton electron screening of water (43) ( Table I).…”

Temperature dependence of the magnetic volume susceptibility of human breast fat tissue: an NMR study

“…In a previous work, heating experiments were conducted which showed that a temperature dependence of the susceptibility of ∼0.005 ppm/ • C leads to errors in MR temperature measurements [4]. The current work shows that human breast fat experiences heating-induced susceptibility changes.…”

“…Heating-induced susceptibility changes may therefore lead to errors in PRFS-based MR thermometry measurements during thermal therapy in tissues with high fat content, even when fat suppression techniques are employed. This has previously been shown for breast tumor ablation using High Intensity Focused Ultrasound (HIFU) [4].…”

Measuring temperature using MRI: a powerful and versatile technique

“…As Sprinkhuizen et al [13] have shown previously in a study of fatty breast tissue, a temperature change of 30 K can lead to a PRF-shift temperature error of almost 10 K. To better model and ideally to correct these fat susceptibility changes, they measured [9] the magnetic volume susceptibility change with the temperature of breast fat tissue samples from six donors. They found a linear dependence of the fat susceptibility with temperature, although the temperature coefficient varied widely from 0.0039 to 0.0076 ppm/K, and the absolute susceptibility values also showed a wide range.…”