Evaluation of heterogeneous metabolic profile in an orthotopic human glioblastoma xenograft model using compressed sensing hyperpolarized 3D 13C magnetic resonance spectroscopic imaging

High resolution compressed sensing hyperpolarized (13)C magnetic resonance spectroscopic imaging was applied in orthotopic human glioblastoma xenografts for quantitative assessment of spatial variations in (13)C metabolic profiles and comparison with histopathology. A new compressed sensing sampling design with a factor of 3.72 acceleration was implemented to enable a factor of 4 increase in spatial resolution. Compressed sensing 3D (13)C magnetic resonance spectroscopic imaging data were acquired from a phantom and 10 tumor-bearing rats following injection of hyperpolarized [1-(13)C]-pyruvate using a 3T scanner. The (13)C metabolic profiles were compared with hematoxylin and eosin staining and carbonic anhydrase 9 staining. The high-resolution compressed sensing (13)C magnetic resonance spectroscopic imaging data enabled the differentiation of distinct (13)C metabolite patterns within abnormal tissues with high specificity in similar scan times compared to the fully sampled method. The results from pathology confirmed the different characteristics of (13)C metabolic profiles between viable, non-necrotic, nonhypoxic tumor, and necrotic, hypoxic tissue.

Use of hyperpolarized [1-13C]pyruvate and [2-13C]pyruvate to probe the effects of the anticancer agent dichloroacetate on mitochondrial metabolism in vivo in the normal rat

Development of hyperpolarized technology utilizing dynamic nuclear polarization has enabled the measurement of (13)C metabolism in vivo at very high signal-to-noise ratio (SNR). In vivo mitochondrial metabolism can, in principle, be monitored with pyruvate, which is catalyzed to acetyl-CoA via pyruvate dehydrogenase (PDH). The purpose of this work was to determine whether the compound sodium dichloroacetate (DCA) could aid the study of mitochondrial metabolism with hyperpolarized pyruvate. DCA stimulates PDH by inhibiting its inhibitor, pyruvate dehydrogenase kinase. In this work, hyperpolarized [1-(13)C]pyruvate and [2-(13)C]pyruvate were used to probe mitochondrial metabolism in normal rats. Increased conversion to bicarbonate (+181±69%, P=.025) was measured when [1-(13)C]pyruvate was injected after DCA administration, and increased glutamate (+74±23%, P=.004), acetoacetate (+504±281%, P=.009) and acetylcarnitine (+377±157%, P=.003) were detected when [2-(13)C]pyruvate was used.

Monitoring urea transport in rat kidney in vivo using hyperpolarized ¹³C magnetic resonance imaging

Urea functions as a key osmolyte in the urinary concentrating mechanism of the inner medulla. The urea transporter UT-A1 is upregulated by antidiuretic hormone, facilitating faster equilibration of urea between the lumen and interstitium of the inner medullary collecting duct, resulting in the formation of more highly concentrated urine. New methods in dynamic nuclear polarization, providing ∼50,000-fold enhancement of nuclear magnetic resonance signals in the liquid state, offer a novel means to monitor this process in vivo using magnetic resonance imaging. In this study, we detected significant signal differences in the rat kidney between acute diuretic and antidiuretic states, using dynamic (13)C magnetic resonance imaging following a bolus infusion of hyperpolarized [(13)C]urea. More rapid medullary enhancement was observed under antidiuresis, consistent with known upregulation of UT-A1.

Automated prescription of oblique brain 3D magnetic resonance spectroscopic imaging

Two major difficulties encountered in implementing Magnetic Resonance Spectroscopic Imaging (MRSI) in a clinical setting are limited coverage and difficulty in prescription. The goal of this project was to automate completely the process of 3D PRESS MRSI prescription, including placement of the selection box, saturation bands and shim volume, while maximizing the coverage of the brain. The automated prescription technique included acquisition of an anatomical MRI image, optimization of the oblique selection box parameters, optimization of the placement of outer-volume suppression saturation bands, and loading of the calculated parameters into a customized 3D MRSI pulse sequence. To validate the technique and compare its performance with existing protocols, 3D MRSI data were acquired from six exams from three healthy volunteers. To assess the performance of the automated 3D MRSI prescription for patients with brain tumors, the data were collected from 16 exams from 8 subjects with gliomas. This technique demonstrated robust coverage of the tumor, high consistency of prescription and very good data quality within the T2 lesion.

A serial in vivo 7T magnetic resonance phase imaging study of white matter lesions in multiple sclerosis

Background:

Magnetic resonance (MR) phase imaging using high field MR scanners has demonstrated excellent contrast in multiple sclerosis (MS) lesions that is thought to be closely correlated to the local iron content. This pilot study acquired serial in vivo MR scans at 7T to track the evolution of phase contrast as MS lesions progress.

Methods:

Five MS patients with relapsing–remitting MS were serially scanned for about 2.5 years at 7T using a high resolution T2*-weighted gradient-echo sequence. Magnitude and phase images were reconstructed for each scan and co-registered to their baseline study.

Results:

Five non-enhancing ring and 70 nodular phase lesions were found in the five patients at baseline. None of the baseline phase lesions (including all five ring phase lesions) showed obvious qualitative variation on phase images during the study. Of note, we observed that three magnitude lesions, not initially read as abnormal signal, were either better appreciated using phase contrast imaging (two lesions) or preceded (one lesion) by phase changes.

Conclusion:

The observation that ring phase lesions remained unchanged over 2.5 years of follow-up challenges the notion that such lesions reveal the presence of acute activated iron-rich macrophages. It suggests that either different phenotypes of macrophages persist longer than previously expected or other mechanisms related to tissue injury contribute to the phase contrast.

A first-in-human phase I imaging study using hyperpolarized 1c-13 pyruvate (h-Py) in patients (pts) with localized prostate cancer (l-PCa)

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Background: Preclinical studies demonstrated that the conversion of h-Py to hyperpolarized 13C lactate (h-lac) is detectable on MRI-spectroscopy and is a useful marker of differentiation in PCa. H-Py MRI provides more than 10,000-fold enhancement in signal to noise ratio (SNR), allowing for rapid detection of metabolic alterations in vivo. Hyperpolarized compounds have not been previously studied in man. Methods: Pts with biopsy-proven untreated l-PCa were enrolled in a phase I study of h-Py MRI. Following a modified 3+3 design, 6 pts were enrolled at each dose level (0.14, 0.28 and 0.43 mL/Kg): 3 to monitor kinetics of h-Py, and 3 to evaluate the spatial distribution of metabolism in PCa and normal prostate (nl-P). An expansion cohort of 15 pts explored the biological variability of metabolism. A dynamic nuclear polarization (DNP) system, the first human system anywhere, generated and delivered 230 mM sterile h-Py. IV injection of h-Py was followed by imaging with a 3T MR scanner with custom transmit and receive coils. Monitoring included EKG, vital signs, and laboratory testing. Results: 31 pts were imaged. 23 pts had Gleason (G) 6, 6 pts G7, and 2 pts G8 PCa. Median age was 63 years (range 45-75); median PSA was 5.9 ng/mL (1.88-20.2). No dose limiting toxicities or >grade (gr) 2 toxicity was observed. Toxicity included: gr 1dysgeusia (6 pts), gr 1 hypokalemia, gr 1 hypocalcemia, gr 1 dizziness, and gr 2 diarrhea (1 pt each). Median time from dissolution of the agent to delivery into patients was 66 seconds (43-88). Signals from h-Py and h-Lac were seen in PCa and nl-P at all doses; 0.43 mL/Kg showed the best SNR and discrimination between PCa and nl-P and was therefore established as the phase II dose. There appeared to be an association between h-Lac levels and PCa grade. Conclusions: H-py metabolic imaging has minimal toxicity and provides the ability to discriminate Ca from nl-P based on increased levels of h-lac. The correlation with grade and changes with therapy require further study.

A method for simultaneous echo planar imaging of hyperpolarized ¹³C pyruvate and ¹³C lactate

A rapid echo planar imaging sequence for dynamic imaging of [1-(13)C] lactate and [1-(13)C] pyruvate simultaneously was developed. Frequency-based separation of these metabolites was achieved by spatial shifting in the phase-encoded direction with the appropriate choice of echo spacing. Suppression of the pyruvate-hydrate and alanine resonances is achieved through an optimized spectral-spatial RF waveform. Signal sampling efficiency as a function of pyruvate and lactate excitation angle was simulated using two site exchange models. Dynamic imaging is demonstrated in a transgenic mouse model, and phantom validations of the RF pulse frequency selectivity were performed.

Generating super stimulated-echoes in MRI and their application to hyperpolarized C-13 diffusion metabolic imaging

Stimulated-echoes in MR can be used to provide high sensitivity to motion and flow, creating diffusion and perfusion weighting as well as T(1) contrast, but conventional approaches inherently suffer from a 50% signal loss. The super stimulated-echo, which uses a specialized radio-frequency (RF) pulse train, has been proposed in order to improve the signal while preserving motion and T(1) sensitivity. This paper presents a novel and straightforward method for designing the super stimulated-echo pulse train using inversion pulse design techniques. This method can also create adiabatic designs with an improved response to RF transmit field variations. The scheme was validated in phantom experiments and shown in vivo to improve signal-to-noise ratio (SNR). We have applied a super stimulated-echo to metabolic MRI with hyperpolarized (13)C-labeled molecules. For spectroscopic imaging of hyperpolarized agents, several repetition times are required but only a single stimulated-echo encoding is feasible, which can lead to unwanted motion blurring. To address this, a super stimulated-echo preparation scheme was used in which the diffusion weighting is terminated prior to the acquisition, and we observed a SNR increases of 60% in phantoms and 49% in vivo over a conventional stimulated-echo. Experiments following injection of hyperpolarized [1-(13)C] -pyruvate in murine transgenic cancer models have shown improved delineation for tumors since signals from metabolites within tumor tissues are retained while those from the vasculature are suppressed by the diffusion preparation scheme.

Multi-channel microstrip transceiver arrays using harmonics for high field MR imaging in humans

Radio-frequency (RF) transceiver array design using primary and higher order harmonics for in vivo parallel magnetic resonance imaging imaging (MRI) and spectroscopic imaging is proposed. The improved electromagnetic decoupling performance, unique magnetic field distributions and high-frequency operation capabilities of higher-order harmonics of resonators would benefit transceiver arrays for parallel MRI, especially for ultrahigh field parallel MRI. To demonstrate this technique, microstrip transceiver arrays using first and second harmonic resonators were developed for human head parallel imaging at 7T. Phantom and human head images were acquired and evaluated using the GRAPPA reconstruction algorithm. The higher-order harmonic transceiver array design technique was also assessed numerically using FDTD simulation. Compared with regular primary-resonance transceiver designs, the proposed higher-order harmonic technique provided an improved g-factor and increased decoupling among resonant elements without using dedicated decoupling circuits, which would potentially lead to a better parallel imaging performance and ultimately faster and higher quality imaging. The proposed technique is particularly suitable for densely spaced transceiver array design where the increased mutual inductance among the elements becomes problematic. In addition, it also provides a simple approach to readily upgrade the channels of a conventional primary resonator microstrip array to a larger number for faster imaging.

Flexible transceiver array for ultrahigh field human MR imaging

A flexible transceiver array, capable of multiple-purpose imaging applications in vivo at ultrahigh magnetic fields was designed, implemented and tested on a 7 T MR scanner. By alternately placing coil elements with primary and secondary harmonics, improved decoupling among coil elements was accomplished without requiring decoupling circuitry between resonant elements, which is commonly required in high-frequency transceiver arrays to achieve sufficient element-isolation during radiofrequency excitation. This flexible array design is capable of maintaining the required decoupling among resonant elements in different array size and geometry and is scalable in coil size and number of resonant elements (i.e., number of channels), yielding improved filling factors for various body parts with different geometry and size. To investigate design feasibility, flexibility, and array performance, a multichannel, 16-element transceiver array was designed and constructed, and in vivo images of the human head, knee, and hand were acquired using a whole-body 7 T MR system. Seven Tesla parallel imaging with generalized autocalibrating partially parallel acquisitions (GRAPPA) performed using this flexible transceiver array was also presented.

A practical multinuclear transceiver volume coil for in vivo MRI/MRS at 7 T

A practical multinuclear transceiver RF volume coil with improved efficiency for in vivo small animal (1)H/(13)C/(23)Na MR applications at the ultrahigh magnetic field of 7 T is reported. In the proposed design, the coil's resonance frequencies for (1)H and (13)C are realized by using a traditional double-tuned approach, while the resonant frequency for (23)Na, which is only some 4 MHz away from the (13)C frequency, is tuned based upon (13)C channel by easy-operating capacitive "frequency switches". In contrast to the traditional triple-tuned volume coil, the volume coil with the proposed design possesses less number of resonances, which helps improve the coil efficiency and alleviate the design and operation difficulties. This coil design strategy is advantageous and well suitable for multinuclear MR imaging and spectroscopy studies, particularly in the case where Larmor frequencies of nuclei in question are not separate enough. The prototype multinuclear coil was demonstrated in the desired unshielded design for easy construction and experiment implementation at 7 T. The design method may provide a practical and robust solution to designing multinuclear RF volume coils for in vivo MR imaging and spectroscopy at ultrahigh fields. Finite difference time domain method simulations for evaluating the design and 7-T MR experiment results acquired using the prototype coil are presented.

A dual-tuned quadrature volume coil with mixed λ/2 and λ/4 microstrip resonators for multinuclear MRSI at 7 T

In this work, an eight-element by eight-element dual-tuned quadrature volume coil with a mix of capacitor terminated half-wavelength (λ/2) and quarter-wavelength (λ/4) microstrip resonators is proposed for multinuclear magnetic resonance imaging/spectroscopy studies at 7 T. In the proton channel, λ/2 microstrip resonators with capacitive terminations on both ends are employed for operation at higher frequency of 298.1 MHz; in the heteronucleus channel, capacitor-terminated λ/4 resonators, suitable for low frequency operations, are used to meet the low frequency requirement. This mixed structure design is particularly advantageous for high field heteronuclei magnetic resonance applications with large difference in Larmor frequency of the nuclei in question. The proposed design method makes it much easier to perform frequency tuning for heteronucleus channel using a variable capacitor with a practical capacitance range. As an example, a dual-tuned volume coil for (1)H/(13)C mouse spectroscopic imaging was proposed to demonstrate the feasibility of this method. The finite-difference time-domain method is first used to model this dual-tuned volume coil and calculate the B(1) field distributions at two frequencies. Transmission parameters (S(21)) measured between the proton channel and the carbon channel are -50 dB at 75 MHz and -35 dB at 298 MHz, showing the excellent isolation between the two channels at 7 T. The proton image and (13)C FIDCSI image of a corn oil phantom on the axial plane at 7 T demonstrate the feasibility of the proposed method. A preliminary proton image of a mouse on the sagittal plane is also acquired using the proposed dual-tuned volume coil at 7 T, illustrating a fairly uniform B(1) field and sufficient image coverage for imaging in mice.

Numerical Analysis of Human Sample Effect on RF Penetration and Liver MR Imaging at Ultrahigh Field

Magnetic resonance imaging (MRI) can provide clinically-valuable images for hepatic diseases and has become one of the most promising noninvasive methods in evaluating liver lesions. To facilitate the ultrahigh field human liver MRI, in this work, the RF penetration behavior in the conductive and high dielectric human body at the ultrahigh field of 7 Tesla (7T) is investigated and evaluated using the finite-difference time-domain numerical analysis. The study shows that in brain imaging at the ultrahigh field of 7T, the "dielectric resonance" effect dominates among other factors, resulting in improved B(1) penetration; while in liver imaging, due to its irregular geometry of the liver, the "dielectric resonance" effect is not readily to be established, leading to a reduced B(1) penetration or limited image coverage comparing to that in the brain. Therefore, it is necessary to build a large size coil to have deeper penetration to image human liver although the coil design may become more challenging due to the required high frequency. Based on this study, a bisected microstrip coil operating at 300 MHz range is designed and constructed. Three-dimensional in vivo liver images in axial, sagittal and coronal orientations are then acquired from healthy volunteers using this dedicated RF coil on a 7T whole body MR scanner.

In vivo measurement of normal rat intracellular pyruvate and lactate levels after injection of hyperpolarized [1-(13)C]alanine

Hyperpolarized technology utilizing dynamic nuclear polarization has enabled rapid and high-sensitivity measurements of (13)C metabolism in vivo. The most commonly used in vivo agent for hyperpolarized (13)C metabolic imaging thus far has been [1-(13)C]pyruvate. In preclinical studies, not only is its uptake detected, but also its intracellular enzymatic conversion to metabolic products including [1-(13)C]lactate and [1-(13)C]alanine. However, the ratio of (13)C-lactate/(13)C-pyruvate measured in this data does not accurately reflect cellular values since much of the [1-(13)C]pyruvate is extracellular depending on timing, vascular properties, and extracellular space and monocarboxylate transporter activity. In order to measure the relative levels of intracellular pyruvate and lactate, in this project we hyperpolarized [1-(13)C]alanine and monitored the in vivo conversion to [1-(13)C]pyruvate and then the subsequent conversion to [1-(13)C]lactate. The intracellular lactate-to-pyruvate ratio of normal rat tissue measured with hyperpolarized [1-(13)C]alanine was 4.89±0.61 (mean±S.E.) as opposed to a ratio of 0.41±0.03 when hyperpolarized [1-(13)C]pyruvate was injected.

Parallel traveling-wave MRI: a feasibility study

Traveling-wave magnetic resonance imaging utilizes far fields of a single-piece patch antenna in the magnet bore to generate radio frequency fields for imaging large-size samples, such as the human body. In this work, the feasibility of applying the "traveling-wave" technique to parallel imaging is studied using microstrip patch antenna arrays with both the numerical analysis and experimental tests. A specific patch array model is built and each array element is a microstrip patch antenna. Bench tests show that decoupling between two adjacent elements is better than -26-dB while matching of each element reaches -36-dB, demonstrating excellent isolation performance and impedance match capability. The sensitivity patterns are simulated and g-factors are calculated for both unloaded and loaded cases. The results on B 1- sensitivity patterns and g-factors demonstrate the feasibility of the traveling-wave parallel imaging. Simulations also suggest that different array configuration such as patch shape, position and orientation leads to different sensitivity patterns and g-factor maps, which provides a way to manipulate B(1) fields and improve the parallel imaging performance. The proposed method is also validated by using 7T MR imaging experiments.

Imaging of blood flow using hyperpolarized [(13)C]urea in preclinical cancer models

PURPOSE

To demonstrate dynamic imaging of a diffusible perfusion tracer, hyperpolarized [(13)C]urea, for regional measurement of blood flow in preclinical cancer models.

MATERIALS AND METHODS

A pulse sequence using balanced steady state free precession (bSSFP) was developed, with progressively increasing flip angles for efficient sampling of the hyperpolarized magnetization. This allowed temporal and volumetric imaging of the [(13)C]urea signal. Regional signal dynamics were quantified for kidneys and liver, and estimates of relative blood flows were derived from the data. Detailed perfusion simulations were performed to validate the methodology.

RESULTS

Significant differences were observed in the signal patterns between normal and cancerous murine hepatic tissues. In particular, a 19% reduction in mean blood flow was observed in tumors, with 26% elevation in the tumor rim. The blood flow maps were also compared with metabolic imaging results with hyperpolarized [1-(13)C]pyruvate.

CONCLUSION

Regional assessment of perfusion is possible by imaging of hyperpolarized [(13)C]urea, which is significant for the imaging of cancer.

Improved spatial coverage for brain 3D PRESS MRSI by automatic placement of outer-volume suppression saturation bands

PURPOSE

To develop a technique for optimizing coverage of brain 3D (1) H magnetic resonance spectroscopic imaging (MRSI) by automatic placement of outer-volume suppression (OVS) saturation bands (sat bands) and to compare the performance for point-resolved spectroscopic sequence (PRESS) MRSI protocols with manual and automatic placement of sat bands.

MATERIALS AND METHODS

The automated OVS procedure includes the acquisition of anatomic images from the head, obtaining brain and lipid tissue maps, calculating optimal sat band placement, and then using those optimized parameters during the MRSI acquisition. The data were analyzed to quantify brain coverage volume and data quality.

RESULTS

3D PRESS MRSI data were acquired from three healthy volunteers and 29 patients using protocols that included either manual or automatic sat band placement. On average, the automatic sat band placement allowed the acquisition of PRESS MRSI data from 2.7 times larger brain volumes than the conventional method while maintaining data quality.

CONCLUSION

The technique developed helps solve two of the most significant problems with brain PRESS MRSI acquisitions: limited brain coverage and difficulty in prescription. This new method will facilitate routine clinical brain 3D MRSI exams and will be important for performing serial evaluation of response to therapy in patients with brain tumors and other neurological diseases.

Multi-band frequency encoding method for metabolic imaging with hyperpolarized [1-(13)C]pyruvate

A new method was developed for simultaneous spatial localization and spectral separation of multiple compounds based on a single echo, by designing the acquisition to place individual compounds in separate frequency encoding bands. This method was specially designed for rapid and robust metabolic imaging of hyperpolarized (13)C substrates and their metabolic products, and was investigated in phantom studies and studies in normal mice and transgenic models of prostate cancer to provide rapid metabolic imaging of hyperpolarized [1-(13)C]pyruvate and its metabolic products [1-(13)C]lactate and [1-(13)C]alanine at spatial resolutions up to 3mm in-plane. Elevated pyruvate and lactate signals in the vicinity of prostatic tissues were observed in transgenic tumor mice. The multi-band frequency encoding technique enabled rapid metabolic imaging of hyperpolarized (13)C compounds with important advantages over prior approaches, including less complicated acquisition and reconstruction methods.

Ultrashort echo time MRI of cortical bone at 7 tesla field strength: a feasibility study

PURPOSE

To implement and examine the feasibility of a three-dimensional (3D) ultrashort TE (UTE) sequence on a 7 Tesla (T) clinical MR scanner in comparison with 3T MRI at high isotropic resolution.

MATERIALS AND METHODS

Using an in-house built saddle coil at both field strengths we have imaged mid-diaphysial sections of five fresh cadaveric specimens of the distal tibia. An additional in vivo scan was performed at 7 Tesla using a quadrature knee coil.

RESULTS

Using the same type of saddle coil at both field strengths, a significant increase in SNR at 7T compared with 3T (factor 1.7) was found. Significantly shorter T2* values were found at the higher field strength (T2* = 552.2 ± 126 μs at 7T versus T2* = 1163 ± 391 μs at 3T).

CONCLUSION

UHF MRI at 7T has great potential for imaging tissues with short T2.

Correlation of phospholipid metabolites with prostate cancer pathologic grade, proliferative status and surgical stage - impact of tissue environment

This study investigates the relationship between phospholipid metabolite concentrations, Gleason score, rate of cellular proliferation and surgical stage in malignant prostatectomy samples by performing one- and two-dimensional, high-resolution magic angle spinning, total correlation spectroscopy, pathology and Ki-67 staining on the same surgical samples. At radical prostatectomy, surgical samples were obtained from 49 patients [41 with localized TNM stage T1 and T2, and eight with local cancer spread (TNM stage T3)]. Thirteen of the tissue samples were high-grade prostate cancer [Gleason score: 4 + 3 (n = 7); 4 + 4 (n = 6)], 22 low-grade prostate cancer [Gleason score: 3 + 3 (n = 17); 3 + 4 (n = 5)] and 14 benign prostate tissues. This study demonstrates that high-grade prostate cancer shows significantly higher Ki-67 staining and concentrations of phosphocholine (PC) and glycerophosphocholine (GPC) than does low-grade prostate cancer (2.4 ± 2.8% versus 7.6 ± 3.5%, p < 0.005, and 0.671 ± 0.461 versus 1.87 ± 2.15 mmolal, p < 0.005, respectively). In patients with local cancer spread, increases in [PC + GPC + PE + GPE] (PE, phosphoethanolamine; GPE, glycerophosphoethanolamine] and Ki-67 index approached significance (4.2 ± 2.5 versus 2.7 ± 2.4 mmolal, p = 0.07, and 5.3 ± 3.8% versus 2.9 ± 3.8%, p = 0.07, respectively). PC and Ki-67 were significantly lower and GPC higher in prostate tissues when compared with cell cultures, presumably because of a lack of important stromal-epithelial interactions in cell cultures. The findings of this study will need to be validated in a larger cohort of surgical patients with clinical outcome data, but support the role of in vivo (1)H MRSI in discriminating between low- and high-grade prostate cancer based on the magnitude of elevation of the in vivo total choline resonance.

Detection of early response to temozolomide treatment in brain tumors using hyperpolarized 13C MR metabolic imaging

PURPOSE

To demonstrate the feasibility of using DNP hyperpolarized [1-(13)C]-pyruvate to measure early response to temozolomide (TMZ) therapy using an orthotopic human glioblastoma xenograft model.

MATERIALS AND METHODS

Twenty athymic rats with intracranial implantation of human glioblastoma cells were divided into two groups: one group received an oral administration of 100 mg/kg TMZ (n = 10) and the control group received vehicle only (n = 10). (13)C 3D magnetic resonance spectroscopic imaging (MRSI) data were acquired following injection of 2.5 mL (100 mM) hyperpolarized [1-(13)C]-pyruvate using a 3T scanner prior to treatment (day D0), at D1 (days from treatment) or D2.

RESULTS

Tumor metabolism as assessed by the ratio of lactate to pyruvate (Lac/Pyr) was significantly altered at D1 for the TMZ-treated group but tumor volume did not show a reduction until D5 to D7. The percent change in Lac/Pyr from baseline was statistically different between the two groups at D1 and D2 (P < 0.008), while percent tumor volume was not (P > 0.2).

CONCLUSION

The results from this study suggest that metabolic imaging with hyperpolarized [1-(13)C]-pyruvate may provide a unique tool that clinical neuro-oncologists can use in the future to monitor tumor response to therapy for patients with brain tumors.

MR spectroscopy of normative premature newborns

PURPOSE

To establish normative metabolite ratios throughout the newborn brain using three-dimensional (3D) MR spectroscopic imaging (MRSI).

MATERIALS AND METHODS

MRI and MRSI have been valuable tools for assessing normal and abnormal neuronal maturation for newborns. In this study, we performed whole brain 3D MRSI in addition to comprehensive anatomic and other functional imaging methods to examine maturation. Fifty-five newborn subjects (28.4 ± 2.6 weeks postconception age at birth, 34.1 ± 3.1 weeks postconception age at scan, 32 males and 23 females) had high quality MRSI studies (104 exams) and normal neurodevelopmental outcome (neuromotor score = 0, mental development index score > 85) at age 12 months.

RESULTS

The NAA to Cho ratio increased significantly with age for all regions. Lac to NAA ratio decreased significantly with age in the regions of thalamus, basal ganglia, cortical spinal tract, and parietal white matter, and showed a decreasing trend in the other regions.

CONCLUSION

Brain metabolites can be obtained through in vivo 3D MRSI and used to monitor newborn brain maturation.

Post-processing correction of the endorectal coil reception effects in MR spectroscopic imaging of the prostate

PURPOSE

To develop and validate a post-processing correction algorithm to remove the effect of the inhomogeneous reception profile of the endorectal coil on MR spectroscopic imaging (MRSI) data.

MATERIALS AND METHODS

A post-processing algorithm to correct for the endorectal coil reception effects on MRSI data was developed based upon theoretical modeling of the endorectal coil reception profile and of the spatial saturation pulse profiles. This algorithm was evaluated on three-dimensional (3D) MRSI data acquired at 3T from a uniform phantom and from 18 patients with known or suspected prostate cancer.

RESULTS

For the phantom data, the coefficient of variation of metabolite peak areas decreased 16% to 46% and the peak area distributions became more Gaussian with correction, as demonstrated by higher Q-Q plot linear correlations (R(2) = 0.98 +/- 0.007 vs. R(2) = 0.89 +/- 0.066). Across the 18 patients, the mean coefficient of variation for suppressed water decreased significantly, from 0.95 +/- 0.18, to 0.66 +/- 0.11, (P < 10(-6), paired t-test) and the linear correlations of the Q-Q plots for the suppressed water increased from R(2) = 0.91 to R(2) = 0.95 (P = 0.0083, paired t-test) with correction.

CONCLUSION

An algorithm for reducing the effect of the inhomogeneous reception profile in endorectal coil acquired 3D MRSI prostate data was demonstrated, illustrating increased homogeneity and more Gaussian peak area distributions.

Evaluation of Common RF Coil Setups for MR Imaging at Ultrahigh Magnetic Field: A Numerical Study

This study is an evaluation of the ratio of electric field to magnetic field (E/B₁), specific absorption rate (SAR) and signal-to-noise ratio (SNR) generated by three different RF transceiver coil setups: surface coil, surface coil with shielding, and microstrip using a finite discrete time domain (FDTD) simulation in the presence of a head phantom. One of our main focuses in this study is to better understand coil designs that would improve patient safety at high fields by studying a coil type that may potentially minimize SAR while examining potential changes in SNR. In the presence of a human head load, the microstrip's E/B₁ ratio was on average smallest while its SAR was also on average smallest of the three setups, suggesting the microstrip may be a better RF coil choice for MRI concerning patient safety and parallel excitation applications than the other two coils. In addition, the study suggests that the microstrip also has a higher SNR compared with the other two coils demonstrating the possibility that the microstrip could lead to higher quality MRI images.

Hippocampal CA1 apical neuropil atrophy in mild Alzheimer disease visualized with 7-T MRI

OBJECTIVES

In Alzheimer disease (AD), mounting evidence points to a greater role for synaptic loss than neuronal loss. Supporting this notion, multiple postmortem studies have demonstrated that the hippocampal CA1 apical neuropil is one of the earliest sites of pathology, exhibiting tau aggregates and then atrophy before there is substantial loss of the CA1 pyramidal neurons themselves. In this cross-sectional study, we tested whether tissue loss in the CA1 apical neuropil layer can be observed in vivo in patients with mild AD.

METHODS

We performed ultra-high-field 7-T MRI on subjects with mild AD (n = 14) and age-matched normal controls (n = 16). With a 2-dimensional T2*-weighted gradient-recalled echo sequence that was easily tolerated by subjects, we obtained cross-sectional slices of the hippocampus at an in-plane resolution of 195 μm.

RESULTS

On images revealing the anatomic landmarks of hippocampal subfields and strata, we observed thinning of the CA1 apical neuropil in subjects with mild AD compared to controls. By contrast, the 2 groups exhibited no difference in the thickness of the CA1 cell body layer or of the entire CA1 subfield. Hippocampal volume, measured on a conventional T1-weighted sequence obtained at 3T, also did not differentiate these patients with mild AD from controls.

CONCLUSIONS

CA1 apical neuropil atrophy is apparent in patients with mild AD. With its superior spatial resolution, 7-T MRI permits in vivo analysis of a very focal, early site of AD pathology.