In vivo ³¹P MR spectroscopic imaging of the human prostate at 7 T: Safety and feasibility

Abstract

(31)P MR spectroscopic imaging of the human prostate provides information about phosphorylated metabolites that could be used for prostate cancer characterization. The sensitivity of a magnetic field strength of 7 T might enable 3D (31)P MR spectroscopic imaging with relevant spatial resolution in a clinically acceptable measurement time. To this end, a (31)P endorectal coil was developed and combined with an eight-channel (1)H body-array coil to relate metabolic information to anatomical location. An extensive safety validation was performed to evaluate the specific absorption rate, the radiofrequency field distribution, and the temperature distribution of both coils. This validation consisted of detailed Finite Integration Technique simulations, confirmed by MR thermometry and B 1+ measurements in a phantom and in vivo temperature measurements. The safety studies demonstrated that the presence of the (31)P endorectal coil had no influence on the specific absorption rate levels and temperature distribution of the external eight-channel (1)H array coil. To stay within a 10 g averaged local specific absorption rate of 10 W/kg, a maximum time-averaged input power of 33 W for the (1)H array coil was allowed. For transmitting with the (31)P endorectal coil, our safety limit of less than 1°C temperature increase in vivo during a 15-min MR spectroscopic imaging experiment was reached at a time-averaged input power of 1.9 W. With this power setting, a second in vivo measurement was performed on a healthy volunteer. Using adiabatic excitation, 3D (31)P MR spectroscopic imaging produced spectra from the entire prostate in 18 min with a spatial resolution of 4 cm(3). The spectral resolution enabled the separate detection of phosphocholine, phosphoethanolamine, inorganic phosphate, and other metabolites that could play an important role in the characterization of prostate cancer.

QuantitativeIn VivoCharacterization of Intracellular and Extracellular pH Profiles in Heterogeneous Tumors: A Novel Method Enabling Multiparametric pH Analysis

“…Although noninvasive determination of intra-and extracellular pH (pH i and pH e ) in mammals, notably by way of nuclear magnetic resonance (NMR) techniques, has become more common in recent years, there is at present no method that provides quantitative parameters specifically characterizing the heterogeneity of pH i and pH e in a given tissue volume. Yet, there is a genuine need for such measurements as a variety of pathologies (cancer and inflammation, among others) are associated with heterogeneous pH regulation (1)(2)(3). Even normal activity such as muscle exercise can generate complex tissue pH distributions as a function of biologic characteristics (4).…”

31P MR spectroscopic imaging of the human prostate at 7 T: T1relaxation times, Nuclear Overhauser Effect, and spectral characterization

“…To localize 31 P MR spectra accurately, proper anatomical MR images first must be acquired. Recently, we showed that anatomical imaging and threedimensional (3-D) 31 P MRSI of the prostate can be performed safely at 7 T with a combination of an eightchannel 1 H transmit=receive (TxRx) coil setup and a 31 P TxRx endorectal loop coil (15). We also demonstrated the feasibility of 3D 31 P MRSI within a clinically acceptable measurement time at 7 T. The 31 P MR spectra obtained from the prostate of a healthy volunteer revealed separate resonances for PE and PC.…”

“…1 H SAR was monitored using a custom-built online RF supervision system (15,25). On average, 23% of the allowed power over 6 min was used during the NOE measurements.…”

Multinuclear magnetic resonance evaluation of tumor tissue

“…Due to the high level of water soluble Cho metabolites in cancer tissue, 31 P MRS is often used to monitor the synthesis of PCho (Katz-Brull et al, 2002). Recently, 31 P MR was used to study metabolite profiles of several types of cancer including glioblastoma (Al-Saffar et al, 2014), ovarian (Abramov et al, 2012), prostate (Kobus et al, 2012), liver (Qi et al, 2011), colorectal (Silberhumer et al, 2009), human extremity sarcomas (Sijens, 1998), non-Hodgkin's lymphomas (Negendank et al, 1995) and focal hepatic malignancies (Cox et al, 1992).…”