Nuclear magnetic resonance imaging of water motion in plants

This Thesis treats one of the new techniques in plant science i.e. nuclear magnetic resonance imaging (NMRi) applied to water motion in plants. It is a challenge, however, to measure this motion in intact plants quantitatively, because plants impose specific problems when studied using NMRi. At high magnetic field strength air-filled intercellular spaces in the plant tissue cause susceptibility-related local magnetic field inhomogeneities, which are much smaller at low magnetic field strength. The inherently low signal-to-noise ratio at low magnetic fields is compensated by the possibility to record a long train of spin-echoes, since generally the spin-spin relaxation time T 2 at low magnetic field is longer than at high magnetic field.In this Thesis the spin echo train is used to shorten the time to produce an NMR image. As a result, time-dependent flow phenomena can be followed at a physiologically relevant time scale using dynamic NMRi employing either a pulsed field gradient (PFG) spin echo sequence (for fast flow, Chapter 2) or a PFG stimulated echo motion-encoding sequence (for slow flow, Chapter 3). Using the quantification method presented in this Thesis (Chapter 4) a number of flow characteristics can be determined for every pixel in an image of a plant stem:the total amount of water,the amount of stationary water,the amount of flowing water,the mean linear flow velocity of the flowing water andthe volumetric flow.These flow characteristics, together with the water density (or total amount of water) and the T 2 value per pixel (measured with quantitative T 2 imaging), were studied in the stem of a cucumber plant as a function of the day-night cycle and cooling of the root system. Root cooling results in inhibition of the water uptake and xylem- and phloem transport, and causes severe wilting of the plant leaves. Following root cooling, during recovery of the plant from its wilted state, the T 2 -values of tissue around the vascular bundles strongly decrease, which may indicate an increased membrane permeability for water of the tissue cells in this period (Chapter 5).During root cooling, large negative pressures in the plant xylem cause cavitations in the vessels, blocking further water transport. In this Thesis the first direct in vivo observations of refilling of cavitated xylem vessels are presented (Chapter 6). This refilling takes many hours and occurs while nearby vessels are under tension and are transporting water. This finding has important implications for the mechanism underlying the refilling process: water entering the refilling vessel must be hydraulically isolated from flowing water in nearby vessels.The strategy (Chapter 7) and methodology of quantitative flow and T 2 NMR imaging, discussed in this Thesis has opened new ways to find answers to longstanding questions in plant science.</p

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 &lt; 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

Imaging Hyperpolarized Pyruvate and Lactate after Blood-Brain Barrier Disruption with Focused Ultrasound

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Processes and xylem anatomical properties involved in rehydration dynamics of cut flowers

In cut flowers, which are harvested in air and transported dry, all cut xylem vessels in the basal part of the stem contain air instead of water. These air-emboli initially block water transport at the start of vase life, but usually (partly) disappear during the first hours of vase life, resulting in rehydration of the flower. However, in some cases flowers are not able to sufficiently remove these air blockages, resulting in a poor water status expressed by wilting. Differences in rehydration ability are present between cultivars, but also between different lots of flowers within one cultivar as result of growing conditions. Using chrysanthemum cut flowers, investigations are focussed on the dynamics of the flower water status during the first hours of vase life after air entrance in the xylem vessels via the cut surface. Role of xylem anatomy in the process related to the establishment of a good or bad rehydration are studied by means of cryo-SEM and other microscopic techniques, dynamic measurements of stem hydraulic resistance and 1H NMR imaging. Modeling techniques are use to explore theoretical concepts and to integrate experimental results obtained by the different experimental techniques

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

Item does not contain fulltextMagnetic 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 © 2013 John Wiley & Sons, Ltd

The Role of Magnetic Resonance Imaging in (Future) Cancer Staging: Note the Nodes

The presence or absence of lymph node metastases is a very important prognostic factor in patients with solid tumors. Current invasive and noninvasive diagnostic methods for N-staging like lymph node dissection, morphologic computed tomography/magnetic resonance imaging (MRI), or positron emission tomography-computed tomography have significant limitations because of technical, biological, or anatomical reasons. Therefore, there is a great clinical need for more precise, reliable, and noninvasive N-staging in patients with solid tumors. Using ultrasmall superparamagnetic particles of ironoxide (USPIO)-enhanced MRI offers noninvasive diagnostic possibilities for N-staging of different types of cancer, including the 4 examples given in this work (head and neck cancer, esophageal cancer, rectal cancer, and prostate cancer). The excellent soft tissue contrast of MRI and an USPIO-based differentiation of metastatic versus nonmetastatic lymph nodes can enable more precise therapy and, therefore, fewer side effects, essentially in cancer patients in oligometastatic disease stage. By discussing 3 important questions in this article, we explain why lymph node staging is so important, why the timing for more accurate N-staging is right, and how it can be done with MRI. We illustrate this with the newest developments in magnetic resonance methodology enabling the use of USPIO-enhanced MRI at ultrahigh magnetic field strength and in moving parts of the body like upper abdomen or mediastinum. For prostate cancer, a comparison with radionuclide tracers connected to prostate specific membrane antigen is made. Under consideration also is the use of MRI for improvement of ex vivo cancer diagnostics. Further scientific and clinical development is needed to assess the accuracy of USPIO-enhanced MRI of detecting small metastatic deposits for different cancer types in different anatomical locations and to broaden the indications for the use of (USPIO-enhanced) MRI in lymph node imaging in clinical practice

3D MR thermometry of frozen tissue: Feasibility and accuracy during cryoablation at 3T

Item does not contain fulltextPURPOSE: To assess the feasibility and accuracy of 3D ultrashort echo time (UTE) magnetic resonance (MR) thermometry of frozen tissue during cryoablation on a clinical 3T MR system. MATERIALS AND METHODS: Ex vivo porcine muscle specimens (n = 4) were imaged during two cycles of 10:3 minutes freeze-thaw on a 3T clinical MR scanner. Continuous MR monitoring was performed using a 3D radial ramp-sampled UTE sequence with a shortest TE of 70 mus. Fiber optic sensors were used for temperature reference. Data of three experiments were used as reference sets. Signal intensity values were normalized to baseline before cooling and related to temperature. Data for subzero temperatures were fit to a monoexponential function. In the separate validation set, the obtained fit was used to generate 3D MR temperature maps of frozen tissue at each imaging timepoint. Statistical analysis was performed to assess accuracy of the MR temperature maps. RESULTS: With 3D UTE imaging, MR signal was measured from frozen tissue down to temperatures as low as -40 degrees C. Temperatures predicted from the MR temperature maps strongly correlated with sensor recorded values (r = 0.977, P < 0.001). Bland-Altman analysis demonstrated a mean difference between MR-estimated temperatures and sensor readings of -1.2 +/- 2.7 degrees C with upper and lower limits of agreement of +4.1 and -6.5 degrees C, respectively. CONCLUSION: 3D MR thermometry of frozen tissue using UTE signal intensity was feasible during cryoablation on a clinical 3T MR system. Down to temperatures as low as -40 degrees C, accuracy of the MR temperature maps was within clinically acceptable limits. J. Magn. Reson. Imaging 2016;44:1572-1579

Developments in proton MR spectroscopic imaging of prostate cancer

In this paper, we review the developments of (1)H-MR spectroscopic imaging (MRSI) methods designed to investigate prostate cancer, covering key aspects such as specific hardware, dedicated pulse sequences for data acquisition and data processing and quantification techniques. Emphasis is given to recent advancements in MRSI methodologies, as well as future developments, which can lead to overcome difficulties associated with commonly employed MRSI approaches applied in clinical routine. This includes the replacement of standard PRESS sequences for volume selection, which we identified as inadequate for clinical applications, by sLASER sequences and implementation of (1)H MRSI without water signal suppression. These may enable a new evaluation of the complementary role and significance of MRSI in prostate cancer management

Quantitative Evaluation of Computed High b Value Diffusion-Weighted Magnetic Resonance Imaging of the Prostate

Item does not contain fulltextComputed diffusion-weighted magnetic resonance imaging (cDWI) refers to the synthesizing of arbitrary b value diffusion-weighted images (DWI) from a set of measured b value images by voxelwise fitting. The objectives of this study were to quantitatively analyze the noise and the contrast-to-noise ratio (CNR) in cDWI as a function of b value by numerical simulations and by measurements in patients with prostate cancer and to compare cDWI to directly measured DWI at a b value of 1400 s/mm.Numerical simulations were performed to assess image noise and CNR in both cDWI and regular DWI. Forty-two patients with prostate cancer (age, 51-73 years; prostate specific antigen level, 0.5-30 ng/mL; and biopsy Gleason score, 6-9) received 2 DWI examinations at 3.0 T (one with b values of 100, 500, and 1400 s/mm and another with b values of 0, 100, 400, and 800 s/mm) to create cDWI images at arbitrary b values, both with and without incorporating a b value of 0 s/mm in their calculation. Regions of interest were drawn to compare the scan time adjusted CNR (CNReff) between cDWI and directly measured DWI at b = 1400 s/mm on tumor-suspicious lesions and normal-appearing regions.In the numerical simulations, noise depended strongly on the b value, the diffusion coefficient, and the signal intensity at a b value of 0 s/mm in cDWI but not in regular DWI. The CNR between simulated tumor and normal regions showed a continuous increase with increasing b value. Both these findings were also observed in tumor-suspicious and normal-appearing regions in in vivo data. In vivo prostate DWI at a b value of 1400 s/mm showed a similar CNReff between the tumor-suspicious regions and the normal-appearing tissue in cDWI as in the directly measured DWI (P = 0.395).The CNReff between tumor-suspicious and normal-appearing prostate tissue in DWI images at a b value of 1400 s/mm is comparable in cDWI and directly measured DWI. Computed DWI at even higher b values, calculated from measured images with b values between 0 and 800 s/mm, yields higher CNReff than measured DWI, which may be of clinical aid in the management of prostate cancer