A multitransmit external body array combined with a (1) H and (31) P endorectal coil to enable a multiparametric and multimetabolic MRI examination of the prostate at 7T

Item does not contain fulltextPURPOSE: In vivo (1) H and (31) P magnetic resonance spectroscopic imaging (MRSI) provide complementary information on the biology of prostate cancer. In this work we demonstrate the feasibility of performing multiparametric imaging (mpMRI) and (1) H and (31) P spectroscopic imaging of the prostate using a (31) P and (1) H endorectal radiofrequency coil (ERC) in combination with a multitransmit body array at 7 Tesla (T). METHODS: An ERC with a (31) P transceiver loop coil and (1) H receive (Rx) asymmetric microstrip ((31) P/(1) H ERC) was designed, constructed and tested in combination with an external 8-channel (1) H transceiver body array coil (8CH). Electromagnetic field simulations and measurements and in vivo temperature measurements of the ERC were performed for safety validation. In addition, the signal-to-noise (SNR) benefit of the (1) H microstrip with respect to the 8CH was evaluated. Finally, the feasibility of the setup was tested in one volunteer and three patients with prostate cancer by performing T2 -weighted and diffusion-weighted imaging in combination with (1) H and (31) P spectroscopic imaging. RESULTS: Electromagnetic field simulations of the (31) P loop coil showed no differences in the E- and B-fields of the (31) P/(1) H ERC compared with a previously safety validated ERC without (1) H microstrip. The hotspot of the specific absorption rate (SAR) at the feed point of the (31) P/(1) H ERC loop coil was 9.42 W/kg when transmitting on (31) P at 1 W. Additional in vivo measurements showed a maximum temperature increase at the SAR hotspot of 0.7 degrees C over 6 min on (31) P at 1.9 W transmit (Tx) power, indicating safe maximum power levels. When transmitting with the external (1) H body array at 40W for 2:30 min, the temperature increase around the ERC was < 0.3 degrees C. Up to 3.5 cm into the prostate the (1) H microstrip of the ERC provided higher SNR than the 8CH. The total coil combination allowed acquisition of an mpMRI protocol and the assessment of (31) P and (1) H metabolites of the prostate in all test subjects. CONCLUSION: We developed a setup with a (31) P transceiver and (1) H Rx endorectal coil in combination with an 8-channel transceiver external body array coil and demonstrated its safety and feasibility for obtaining multiparametric imaging and (1) H and (31) P MRSI at 7T in patients with prostate cancer within one MR examination

High resolution MR imaging of pelvic lymph nodes at 7 Tesla

Item does not contain fulltextPURPOSE: Pelvic lymph node (PLN) metastases are often smaller than 5 mm and difficult to detect. This work presents a method to perform PLN imaging with ultrahigh-field MRI, using spectrally selective excitation to acquire water and lipid-selective imaging at high spatial resolution. METHODS: A 3D water-selective multigradient echo (mGRE) sequence and lipid-selective gradient echo (GRE) sequence were tested in six healthy volunteers on a 7 Tesla (T) MRI system, using time interleaved acquisition of modes (TIAMO) to improve image homogeneity. The size distribution of the first 10 iliac PLNs detected in each volunteer was determined, and the contrast-to-noise ratio (CNR) of these lymph nodes (LNs) was compared with the individual mGRE images, sum-of-squares echo addition, and computed T2*-weighted images derived from the T2* fits. RESULTS: LN imaging was acquired robustly at ultrahigh field with high resolution and homogeneous lipid or water-selective contrast. PLNs down to 1.5-mm short axis were detected with mean +/- standard error of the mean (SEM) short and long axes of 2.2 +/- 0.1 and 3.7 +/- 0.2 mm, respectively. Computed T2*-weighted imaging allowed flexibility in T2* contrast while featuring a CNR up to 90% of the sum-of-squares echo addition. CONCLUSION: Ultrahigh-field MRI in combination with TIAMO and frequency-selective excitation enables high-resolution, large field-of-view MRI of the lower abdomen, and may ultimately be suitable for detecting small PLN metastases. Magn Reson Med 78:1020-1028, 2017. (c) 2016 International Society for Magnetic Resonance in Medicine

Automatic frequency and phase alignment of in vivo J-difference-edited MR spectra by frequency domain correlation

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Flexible proton 3D MR spectroscopic imaging of the prostate with low-power adiabatic pulses for volume selection and spiral readout

PURPOSE: Cartesian k-space sampling in three-dimensional magnetic resonance spectroscopic imaging (MRSI) of the prostate limits the selection of voxel size and acquisition time. Therefore, large prostates are often scanned at reduced spatial resolutions to stay within clinically acceptable measurement times. Here we present a semilocalized adiabatic selective refocusing (sLASER) sequence with gradient-modulated offset-independent adiabatic (GOIA) refocusing pulses and spiral k-space acquisition (GOIA-sLASER-Spiral) for fast prostate MRSI with enhanced resolution and extended matrix sizes. METHODS: MR was performed at 3 tesla with an endorectal receive coil. GOIA-sLASER-Spiral at an echo time (TE) of 90 ms was compared to a point-resolved spectroscopy sequence (PRESS) with weighted, elliptical phase encoding at an TE of 145 ms using simulations and measurements of phantoms and patients (n = 9). RESULTS: GOIA-sLASER-Spiral acquisition allows prostate MR spectra to be obtained in approximately 5 min with a quality comparable to those acquired with a common Cartesian PRESS protocol in approximately 9 min, or at an enhanced spatial resolution showing more precise tissue allocation of metabolites. Extended field of views (FOVs) and matrix sizes for large prostates are possible without compromising spatial resolution or measurement time. CONCLUSION: The flexibility of spiral sampling enables prostate MRSI with a wide range of resolutions and FOVs without undesirable increases in acquisition times, as in Cartesian encoding. This approach is suitable for routine clinical exams of prostate metabolites. Magn Reson Med 77:928-935, 2017. (c) 2016 International Society for Magnetic Resonance in Medicine

Can Ex Vivo Magnetic Resonance Imaging of Rectal Cancer Specimens Improve the Mesorectal Lymph Node Yield for Pathological Examination?

Contains fulltext : 208465pub.pdf (publisher's version ) (Open Access)PURPOSE: The aim of this study was to use 7 T ex vivo magnetic resonance imaging (MRI) scans to determine the size of lymph nodes (LNs) in total mesorectal excision (TME) specimens and to increase the pathological yield of LNs with MR-guided pathology. MATERIALS AND METHODS: Twenty-two fixated TME specimens containing adenocarcinoma were scanned on a 7 T preclinical MRI system with a T1-weighted 3-dimensional gradient echo sequence with frequency-selective lipid excitation (repetition time/echo time, 15/3 milliseconds; resolution, 0.293 mm) and a water-excited 3-dimensional multigradient echo (repetition time, 30 milliseconds; computed echo time, 6.2 milliseconds; resolution, 0.293 mm) pulse sequence.The first series of 11 TME specimens (S1) revealed the number and size of LNs on both ex vivo MRI and histopathology. The second series of 11 TME specimens (S2) was used to perform MR-guided pathology. The number, size, and percentages of yielded LNs of S1 and S2 were compared. RESULTS: In all specimens (22/22), a median number of 34 LNs (interquartile range, 26-34) was revealed on ex vivo MRI compared with 14 LNs (interquartile range, 7.5-21.5) on histopathology (P = 0.003). Mean size of all LNs did not differ between the 2 series (ex vivo MRI: 2.4 vs 2.5 mm, P = 0.267; pathology: 3.6 vs 3.5 mm, P = 0.653). The median percentages of harvested LNs compared with nodes visible on ex vivo MRI per specimen for both series were not significantly different (40% vs 43%, P = 0.718). By using a size threshold of greater than 2 mm, the percentage improved to 71% (S1) and to 78% (S2, P = 0.895). The median number of harvested LNs per specimen did not increase by performing MR-guided pathology (S1, 14 LNs; S2, 20 LNs; P = 0.532). CONCLUSIONS: Ex vivo MRI visualizes more LNs than (MR-guided) pathology is able to harvest. Current pathological examination was not further improved by MR guidance. The majority of LNs or LN-like structures visible on ex vivo MRI below 2 mm in size remain unexplained, which warrants a 3-dimensional approach for pathological reconstruction of specimens

Effect of lactate administration on brain lactate levels during hypoglycemia in patients with type 1 diabetes

Administration of lactate during hypoglycemia suppresses symptoms and counterregulatory responses, as seen in patients with type 1 diabetes and impaired awareness of hypoglycemia (IAH), presumably because lactate can substitute for glucose as a brain fuel. Here, we examined whether lactate administration, in a dose sufficient to impair awareness of hypoglycemia, affects brain lactate levels in patients with normal awareness of hypoglycemia (NAH). Patients with NAH (n = 6) underwent two euglycemic-hypoglycemic clamps (2.8 mmol/L), once with sodium lactate infusion (NAH w|lac) and once with saline infusion (NAH w|placebo). Results were compared to those obtained during lactate administration in patients with IAH (n = 7) (IAH w|lac). Brain lactate levels were determined continuously with J-difference editing (1)H-MRS. During lactate infusion, symptom and adrenaline responses to hypoglycemia were considerably suppressed in NAH. Infusion of lactate increased brain lactate levels modestly, but comparably, in both groups (mean increase in NAH w|lac: 0.12 +/- 0.05 micromol/g and in IAH w|lac: 0.06 +/- 0.04 micromol/g). The modest increase in brain lactate may suggest that the excess of lactate is immediately metabolized by the brain, which in turn may explain the suppressive effects of lactate on awareness of hypoglycemia observed in patients with NAH

7T ultra-high field body MR imaging with an 8-channel transmit/32-channel receive radiofrequency coil array

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Feasibility of Multiparametric Magnetic Resonance Imaging of the Prostate at 7 T

Item does not contain fulltextOBJECTIVES: The aim of this study was to evaluate the technical feasibility of prostate multiparametric magnetic resonance imaging (mpMRI) at a magnetic field strength of 7 T. MATERIALS AND METHODS: In this prospective institutional review board-approved study, 14 patients with biopsy-proven prostate cancer (mean age, 65.2 years; median prostate-specific antigen [PSA], 6.2 ng/mL), all providing signed informed consent, underwent 7 T mpMRI with an external 8-channel body-array transmit coil and an endorectal receive coil between September 2013 and October 2014. Image and spectral quality of high-resolution T2-weighted (T2W) imaging (0.3 x 0.3 x 2 mm), diffusion-weighted imaging (DWI; 1.4 x 1.4 x 2 mm or 1.75 x 1.75 x 2 mm), and (H) MR spectroscopic imaging (MRSI; real voxel size, 0.6 mm in 7:16 minutes) were rated on a 5-point scale by 2 radiologists and a spectroscopist. RESULTS: Prostate mpMRI including at least 2 of 3 MR techniques was obtained at 7 T in 13 patients in 65 +/- 12 minutes. Overall T2W and DWI image quality at 7 T was scored as fair (38% and 17%, respectively) to good or very good (55% and 83%, respectively). The main artifacts for T2W imaging were motion and areas of low signal-to-noise ratio, the latter possibly caused by radiofrequency field inhomogeneities. For DWI, the primary artifact was ghosting of the rectal wall in the readout direction. Magnetic resonance spectroscopic imaging quality was rated fair or good in 56% of the acquisitions and was mainly limited by lipid contamination. CONCLUSIONS: Multiparametric MRI of the prostate at 7 T is feasible at unprecedented spatial resolutions for T2W imaging and DWI and within clinically acceptable acquisition times for high-resolution MRSI, using the combination of an external 8-channel body-array transmit coil and an endorectal receive coil. The higher spatial resolutions can yield improved delineation of prostate anatomy, but the robustness of the techniques needs to be improved before clinical adoption of 7 T mpMRI

USPIO-enhanced MRI of lymph nodes in rectal cancer: A node-to-node comparison with histopathology

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