Miriam W. Lagemaat

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

31P 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 31P MR spectroscopic imaging with relevant spatial resolution in a clinically acceptable measurement time. To this end, a 31P endorectal coil was developed and combined with an eight‐channel 1H 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 31P endorectal coil had no influence on the specific absorption rate levels and temperature distribution of the external eight‐channel 1H 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 1H array coil was allowed. For transmitting with the 31P 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 31P MR spectroscopic imaging produced spectra from the entire prostate in 18 min with a spatial resolution of 4 cm3. 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. Magn Reson Med, 2012.

Feasibility of T2 -weighted turbo spin echo imaging of the human prostate at 7 tesla.

To demonstrate that high quality T2‐weighted (T2w) turbo spin‐echo (TSE) imaging of the complete prostate can be achieved routinely and within safety limits at 7 T, using an external transceive body array coil only.

(31) P MR spectroscopic imaging of the human prostate at 7 T: T1 relaxation times, Nuclear Overhauser Effect, and spectral characterization

Optimization of phosphorus (31P) MR spectroscopic imaging (MRSI) of the human prostate at 7 T by the evaluation of T1 relaxation times and the Nuclear Overhauser Effect (NOE) of phosphorus‐containing metabolites.

Role of high‐field MR in studies of localized prostate cancer

Magnetic resonance imaging is attracting increasing attention from the uroradiological community as a modality to guide the management of prostate cancer. With the high incidence of prostate cancer it might come as a surprise that for a very long time (and in many places even at present) treatment decisions were being made without the use of detailed anatomical and functional imaging of the prostate gland at hand. Although T2‐weighted MRI can provide great anatomical detail, by itself it is not specific enough to discriminate cancer from benign disease, so other functional MRI techniques have been explored to aid in detection, localization, staging and risk assessment of prostate cancer. With the current evolution of clinical MR systems from 1.5 to 3 T it is important to understand the advantages and the challenges of the higher magnetic field strength for the different functional MR techniques most used in the prostate: T2‐weighted MRI, diffusion‐weighted MRI, MR spectroscopic imaging and dynamic contrast‐enhanced imaging. In addition to this, the use of the endorectal coil at different field strengths is discussed in this review, together with an outlook of the possibilities of ultra‐high‐field MR for the prostate. Copyright

Image quality and cancer visibility of T2-weighted Magnetic Resonance Imaging of the prostate at 7 Tesla

AbstractObjectivesTo assess the image quality of T2-weighted (T2w) magnetic resonance imaging of the prostate and the visibility of prostate cancer at 7 Tesla (T).Materials & methodsSeventeen prostate cancer patients underwent T2w imaging at 7T with only an external transmit/receive array coil. Three radiologists independently scored images for image quality, visibility of anatomical structures, and presence of artefacts. Krippendorff’s alpha and weighted kappa statistics were used to assess inter-observer agreement. Visibility of prostate cancer lesions was assessed by directly linking the T2w images to the confirmed location of prostate cancer on histopathology.ResultsT2w imaging at 7T was achievable with ‘satisfactory’ (3/5) to ‘good’ (4/5) quality. Visibility of anatomical structures was predominantly scored as ‘satisfactory’ (3/5) and ‘good’ (4/5). If artefacts were present, they were mostly motion artefacts and, to a lesser extent, aliasing artefacts and noise. Krippendorff’s analysis revealed an α = 0.44 between three readers for the overall image quality scores. Clinically significant cancer lesions in both peripheral zone and transition zone were visible at 7T.ConclusionT2w imaging with satisfactory to good quality can be routinely acquired, and cancer lesions were visible in patients with prostate cancer at 7T using only an external transmit/receive body array coil.Key Points• Satisfactory to good T2-weighted image quality of the prostate is achievable at 7T. • Periprostatic lipids appear hypo-intense compared to healthy peripheral zone tissue at 7T. • Prostate cancer is visible on T2-weighted MRI at 7T.

Phosphorus Magnetic Resonance Spectroscopic Imaging at 7 T in Patients With Prostate Cancer

ObjectivesThe aim of this study was to identify characteristics of phosphorus (31P) spectra of the human prostate and to investigate changes of individual phospholipid metabolites in prostate cancer through in vivo 31P magnetic resonance spectroscopic imaging (MRSI) at 7 T. Materials and MethodsIn this institutional review board–approved study, 15 patients with biopsy-proven prostate cancer underwent T2-weighted magnetic resonance imaging and 3-dimensional 31P MRSI at 7 T. Voxels were selected at the tumor location, in normal-appearing peripheral zone tissue, normal-appearing transition zone tissue, and in the base of the prostate close to the seminal vesicles. Phosphorus metabolite ratios were determined and compared between tissue types. ResultsSignals of phosphoethanolamine (PE) and phosphocholine (PC) were present and well resolved in most 31P spectra in the prostate. Glycerophosphocholine signals were observable in 43% of the voxels in malignant tissue, but in only 10% of the voxels in normal-appearing tissue away from the seminal vesicles. In many spectra, independent of tissue type, 2 peaks resonated in the chemical shift range of inorganic phosphate, possibly representing 2 separate pH compartments. The PC/PE ratio in the seminal vesicles was highly elevated compared with the prostate in 5 patients. A considerable overlap of 31P metabolite ratios was found between prostate cancer and normal-appearing prostate tissue, preventing direct discrimination of these tissues. The only 2 patients with high Gleason scores tumors (≥4+5) presented with high PC and glycerophosphocholine levels in their cancer lesions. ConclusionsPhosphorus MRSI at 7 T shows distinct features of phospholipid metabolites in the prostate gland and its surrounding structures. In this exploratory study, no differences in 31P metabolite ratios were observed between prostate cancer and normal-appearing prostate tissue possibly because of the partial volume effects of small tumor foci in large MRSI voxels.

Quantitative short echo time 1H MRSI of the peripheral edematous region of human brain tumors in the differentiation between glioblastoma, metastasis, and meningioma

To assess metabolite levels in peritumoral edematous (PO) and surrounding apparently normal (SAN) brain regions of glioblastoma, metastasis, and meningioma in humans with 1H‐MRSI to find biomarkers that can discriminate between tumors and characterize infiltrative tumor growth.

Reproducibility of 3D 1H MR spectroscopic imaging of the prostate at 1.5T

To determine the reproducibility of 3D proton magnetic resonance spectroscopic imaging (1H‐MRSI) of the human prostate in a multicenter setting at 1.5T.

(1) H MR spectroscopic imaging of the prostate at 7T using spectral-spatial pulses

To assess the feasibility of prostate 1H MR spectroscopic imaging (MRSI) using low‐power spectral‐spatial (SPSP) pulses at 7T, exploiting accurate spectral selection and spatial selectivity simultaneously.

Optimized (31) P MRS in the human brain at 7 T with a dedicated RF coil setup

The design and construction of a dedicated RF coil setup for human brain imaging (1H) and spectroscopy (31P) at ultra‐high magnetic field strength (7 T) is presented. The setup is optimized for signal handling at the resonance frequencies for 1H (297.2 MHz) and 31P (120.3 MHz). It consists of an eight‐channel 1H transmit–receive head coil with multi‐transmit capabilities, and an insertable, actively detunable 31P birdcage (transmit–receive and transmit only), which can be combined with a seven‐channel receive‐only 31P array. The setup enables anatomical imaging and 31P studies without removal of the coil or the patient. By separating transmit and receive channels and by optimized addition of array signals with whitened singular value decomposition we can obtain a sevenfold increase in SNR of 31P signals in the occipital lobe of the human brain compared with the birdcage alone. These signals can be further enhanced by 30 ± 9% using the nuclear Overhauser effect by B1‐shimmed low‐power irradiation of water protons. Together, these features enable acquisition of 31P MRSI at high spatial resolutions (3.0 cm3 voxel) in the occipital lobe of the human brain in clinically acceptable scan times (~15 min).