DC‐gated high resolution three‐dimensional lung imaging during free‐breathing

Purpose:

To use the acquisition of the k‐space center signal (DC signal) implemented into a Cartesian three‐dimensional (3D) FLASH sequence for retrospective respiratory self‐gating and, thus, for the examination of the whole human lung in high spatial resolution during free breathing.

Materials and Methods:

Volunteer as well as patient measurements were performed under free breathing conditions. The DC signal is acquired after the actual image data acquisition within each excitation of a 3D FLASH sequence. The DC signal is then used to track respiratory motion for retrospective respiratory gating.

Results:

It is shown that the acquisition of the DC signal after the imaging module can be used in a 3D FLASH sequence to extract respiratory motion information for retrospective respiratory self‐gating and allows for shorter echo times (TE) and therefore increased lung parenchyma SNR.

Conclusion:

The acquisition of the DC signal after image signal acquisition allows successful retrospective gating, enabling the reconstruction of high resolution images of the whole human lung under free breathing conditions. J. Magn. Reson. Imaging 2013;37:727–732. © 2012 Wiley Periodicals, Inc.     

Lung imaging under free‐breathing conditions

Respiratory motion and pulsatile blood flow can generate artifacts in morphological and functional lung imaging. Total acquisition time, and thus the achievable signal to noise ratio, is limited when performing breath‐hold and/or electrocardiogram‐triggered imaging. To overcome these limitations, imaging during free respiration can be performed using respiratory gating/triggering devices or navigator echoes. However, these techniques provide only poor gating resolution and can induce saturation bands and signal fluctuations into the lung volume. In this work, acquisition schemes for nonphase encoded navigator echoes were implemented into different sequences for morphological and functional lung imaging at 1.5 Tesla (T) and 0.2T. The navigator echoes allow monitoring of respiratory motion and provide an ECG‐trigger signal for correction of the heart cycle without influencing the imaged slices. Artifact free images acquired during free respiration using a 3D GE, 2D multislice TSE or multi‐Gradient Echo sequence for oxygen‐enhanced T quantification are presented. Magn Reson Med, 2009. © 2008 Wiley‐Liss, Inc.     

Lung ventilation‐ and perfusion‐weighted Fourier decomposition magnetic resonance imaging: In vivo validation with hyperpolarized 3He and dynamic contrast‐enhanced MRI

The purpose of this work was to validate ventilation‐weighted (VW) and perfusion‐weighted (QW) Fourier decomposition (FD) magnetic resonance imaging (MRI) with hyperpolarized ³He MRI and dynamic contrast‐enhanced perfusion (DCE) MRI in a controlled animal experiment. Three healthy pigs were studied on 1.5‐T MR scanner. For FD MRI, the VW and QW images were obtained by postprocessing of time‐resolved lung image sets. DCE acquisitions were performed immediately after contrast agent injection. ³He MRI data were acquired following the administration of hyperpolarized helium and nitrogen mixture. After baseline MR scans, pulmonary embolism was artificially produced. FD MRI and DCE MRI perfusion measurements were repeated. Subsequently, atelectasis and air trapping were induced, which followed with FD MRI and ³He MRI ventilation measurements. Distributions of signal intensities in healthy and pathologic lung tissue were compared by statistical analysis. Images acquired using FD, ³He, and DCE MRI in all animals before the interventional procedure showed homogeneous ventilation and perfusion. Functional defects were detected by all MRI techniques at identical anatomical locations. Signal intensity in VW and QW images was significantly lower in pathological than in healthy lung parenchyma. The study has shown usefulness of FD MRI as an alternative, noninvasive, and easily implementable technique for the assessment of acute changes in lung function. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

32‐channel phased‐array receive with asymmetric birdcage transmit coil for hyperpolarized xenon‐129 lung imaging

Hyperpolarized xenon‐129 has the potential to become a noninvasive contrast agent for lung MRI. In addition to its utility for imaging of ventilated airspaces, the property of xenon to dissolve in lung tissue and blood upon inhalation provides the opportunity to study gas exchange. Implementations of imaging protocols for obtaining regional parameters that exploit the dissolved phase are limited by the available signal‐to‐noise ratio, excitation homogeneity, and length of acquisition times. To address these challenges, a 32‐channel receive‐array coil complemented by an asymmetric birdcage transmit coil tuned to the hyperpolarized xenon‐129 resonance at 3 T was developed. First results of spin‐density imaging in healthy subjects and subjects with obstructive lung disease demonstrated the improvements in image quality by high‐resolution ventilation images with high signal‐to‐noise ratio. Parallel imaging performance of the phased‐array coil was demonstrated by acceleration factors up to three in 2D acquisitions and up to six in 3D acquisitions. Transmit‐field maps showed a regional variation of only 8% across the whole lung. The newly developed phased‐array receive coil with the birdcage transmit coil will lead to an improvement in existing imaging protocols, but moreover enable the development of new, functional lung imaging protocols based on the improvements in excitation homogeneity, signal‐to‐noise ratio, and acquisition speed. Magn Reson Med 70:576–583, 2013. © 2012 Wiley Periodicals, Inc.     

High‐resolution spiral imaging on a whole‐body 7T scanner with minimized image blurring

High‐resolution (～0.22 mm) images are preferably acquired on whole‐body 7T scanners to visualize minianatomic structures in human brain. They usually need long acquisition time (～12 min) in three‐dimensional scans, even with both parallel imaging and partial Fourier samplings. The combined use of both fast imaging techniques, however, leads to occasionally visible undersampling artifacts. Spiral imaging has an advantage in acquisition efficiency over rectangular sampling, but its implementations are limited due to image blurring caused by a strong off‐resonance effect at 7T. This study proposes a solution for minimizing image blurring while keeping spiral efficient. Image blurring at 7T was, first, quantitatively investigated using computer simulations and point‐spread functions. A combined use of multishot spirals and ultrashort echo time acquisitions was then employed to minimize off‐resonance‐induced image blurring. Experiments on phantoms and healthy subjects were performed on a whole‐body 7T scanner to show the performance of the proposed method. The three‐dimensional brain images of human subjects were obtained at echo time = 1.18 ms, resolution = 0.22mm (field of view = 220mm, matrix size = 1024), and in‐plane spiral shots = 128, using a home‐developed ultrashort echo time sequence (acquisition‐weighted stack of spirals). The total acquisition time for 60 partitions at pulse repetition time = 100 ms was 12.8 min without use of parallel imaging and partial Fourier sampling. The blurring in these spiral images was minimized to a level comparable to that in gradient‐echo images with rectangular acquisitions, while the spiral acquisition efficiency was maintained at eight. These images showed that spiral imaging at 7T was feasible. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Respiratory motion‐compensated radial dynamic contrast‐enhanced (DCE)‐MRI of chest and abdominal lesions

Dynamic contrast‐enhanced (DCE)‐MRI is becoming an increasingly important tool for evaluating tumor vascularity and assessing the effectiveness of emerging antiangiogenic and antivascular agents. In chest and abdominal regions, however, respiratory motion can seriously degrade the achievable image quality in DCE‐MRI studies. The purpose of this work is to develop a respiratory motion‐compensated DCE‐MRI technique that combines the self‐gating properties of radial imaging with the reconstruction flexibility afforded by the golden‐angle view‐order strategy. Following radial data acquisition, the signal at k‐space center is first used to determine the respiratory cycle, and consecutive views during the expiratory phase of each respiratory period (34–55 views, depending on the breathing rate) are grouped into individual segments. Residual intrasegment translation of lesion is subsequently compensated for by an autofocusing technique that optimizes image entropy, while intersegment translation (among different respiratory cycles) is corrected using 3D image correlation. The resulting motion‐compensated, undersampled dynamic image series is then processed to reduce image streaking and to enhance the signal‐to‐noise ratio (SNR) prior to perfusion analysis, using either the k‐space‐weighted image contrast (KWIC) radial filtering technique or principal component analysis (PCA). The proposed data acquisition scheme also allows for high frame‐rate arterial input function (AIF) sampling and free‐breathing baseline T₁ mapping. The performance of the proposed radial DCE‐MRI technique is evaluated in subjects with lung and liver lesions, and results demonstrate that excellent pixelwise perfusion maps can be obtained with the proposed methodology. Magn Reson Med 60:1135–1146, 2008. © 2008 Wiley‐Liss, Inc.     

Non‐contrast‐enhanced vascular magnetic resonance imaging using flow‐dependent preparation with subtraction

Recent concerns over contrast agent safety have encouraged new developments in non‐contrast‐enhanced vascular imaging techniques. This work investigates the potential for imaging both arteries and veins with vascular anatomy by nonenhanced static subtraction angiography (VANESSA), a method using controllable flow suppression together with subtraction of bright‐ and dark‐blood images. The lower legs of eight healthy volunteers and three patients were imaged using a modified motion‐sensitized driven equilibrium preparation, with three‐dimensional balanced steady‐state free precession readout. The vascular signal decreased with increasing motion‐suppression gradient amplitude, and was suppressed when the velocity‐encoding parameter was (approximately) less than the measured flow velocity. Selected pairs of images were subtracted to depict vessels with either fast flow (e.g. arteries), slow flow (e.g. veins), or both. Several methodological modifications improved image quality and reduced the background signal from static tissues. Subjectively assessed image quality in volunteers was rated as excellent for 56/64 arterial segments, and good or excellent for 35/64 veins. In conclusion, VANESSA enables rapid non‐contrast‐enhanced imaging of arteries and veins, combining information on both morphology and flow. This study demonstrates good technical performance in volunteers and evaluation in patients with vascular disease is warranted. Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc.     

Online real‐time reconstruction of adaptive TSENSE with commodity CPU/GPU hardware

Adaptive temporal sensitivity encoding (TSENSE) has been suggested as a robust parallel imaging method suitable for MR guidance of interventional procedures. However, in practice, the reconstruction of adaptive TSENSE images obtained with large coil arrays leads to long reconstruction times and latencies and thus hampers its use for applications such as MR‐guided thermotherapy or cardiovascular catheterization. Here, we demonstrate a real‐time reconstruction pipeline for adaptive TSENSE with low image latencies and high frame rates on affordable commodity personal computer hardware. For typical image sizes used in interventional imaging (128 × 96, 16 channels, sensitivity encoding (SENSE) factor 2‐4), the pipeline is able to reconstruct adaptive TSENSE images with image latencies below 90 ms at frame rates of up to 40 images/s, rendering the MR performance in practice limited by the constraints of the MR acquisition. Its performance is demonstrated by the online reconstruction of in vivo MR images for rapid temperature mapping of the kidney and for cardiac catheterization. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Multiecho time‐resolved acquisition (META): A high spatiotemporal resolution dixon imaging sequence for dynamic contrast‐enhanced MRI

Purpose

To evaluate a new dynamic contrast‐enhanced (DCE) imaging technique called multiecho time‐resolved acquisition (META) for abdominal/pelvic imaging. META combines an elliptical centric time‐resolved three‐dimensional (3D) spoiled gradient‐recalled echo (SPGR) imaging scheme with a Dixon‐based fat‐water separation algorithm to generate high spatiotemporal resolution volumes.

Materials and Methods

Twenty‐three patients referred for hepatic metastases or renal masses were imaged using the new META sequence and a conventional fat‐suppressed 3D SPGR sequence on a 3T scanner. In 12 patients, equilibrium‐phase 3D SPGR images acquired immediately after META were used for comparing the degree and homogeneity of fat suppression, artifacts, and overall image quality. In the remaining 11 of 23 patients, DCE 3D SPGR images acquired in a previous or subsequent examination were used for comparing the efficiency of arterial phase capture in addition to the qualitative analysis for the degree and homogeneity of fat suppression, artifacts, and overall image quality.

Results

META images were determined to be significantly better than conventional 3D SPGR images for degree and uniformity of fat suppression and ability to visualize the arterial phase. There were no significant differences in artifact levels or overall image quality.

Conclusion

META is a promising high spatiotemporal resolution imaging sequence for capturing the fast dynamics of hyperenhancing hepatic lesions and provides robust fat suppression even at 3T. J. Magn. Reson. Imaging 2009. © 2009 Wiley‐Liss, Inc.     

Half‐fourier‐acquisition single‐shot turbo spin‐echo (HASTE) MRI of the lung at 3 Tesla using parallel imaging with 32‐receiver channel technology

Purpose

To assess the feasibility of half‐Fourier‐acquisition single‐shot turbo spin‐echo (HASTE) of the lung at 3 Tesla (T) using parallel imaging with a prototype of a 32‐channel torso array coil, and to determine the optimum acceleration factor for the delineation of intrapulmonary anatomy.

Materials and Methods

Nine volunteers were examined on a 32‐channel 3T MRI system using a prototype 32‐channel‐torso‐array‐coil. HASTE‐MRI of the lung was acquired at both, end‐inspiratory and end‐expiratory breathhold with parallel imaging (Generalized autocalibrating partially parallel acquisitions = GRAPPA) using acceleration factors ranging between R = 1 (TE = 42 ms) and R = 6 (TE = 16 ms). The image quality of intrapulmonary anatomy and subjectively perceived noise level was analyzed by two radiologists in consensus. In addition quantitative measurements of the signal‐to‐noise ratio (SNR) of HASTE with different acceleration factors were assessed in phantom measurements.

Results

Using an acceleration factor of R = 4 image blurring was substantially reduced compared with lower acceleration factors resulting in sharp delineation of intrapulmonary structures in expiratory scans. For inspiratory scans an acceleration factor of 2 provided the best image quality. Expiratory scans had a higher subjectively perceived SNR than inspiratory scans.

Conclusion

Using optimized multi‐element coil geometry HASTE‐MRI of the lung is feasible at 3T with acceleration factors up to 4. Compared with nonaccelerated acquisitions, shorter echo times and reduced image blurring are achieved. Expiratory scanning may be favorable to compensate for susceptibility associated signal loss at 3T. J. Magn. Reson. Imaging 2009;30:541–546. © 2009 Wiley‐Liss, Inc.     

Validation of simple and robust protocols for high‐resolution lung proton MRI in mice

One fundamental limitation of spatial resolution for in vivo MR lung imaging is related to motion in the thoracic cavity. To overcome this limitation, several methods have been proposed, including scan‐synchronous ventilation and the cardiac gating approach. However, with cardiac and ventilation triggered techniques, the use of a predetermined and constant sequence repetition time is not possible, resulting in variable image contrast. In this study, the potential of two “constant repetition time” approaches based on retrospective self‐gating and signal averaging were investigated for lung imaging. Image acquisitions were performed at a very short echo time for visualization of the lung structures and the parenchyma. Highly spatially resolved images acquired using retrospective self‐gating, signal averaging technique and conventional cardiorespiratory gating are presented and compared. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

CE‐MRA of the lower extremities using HYPR stack‐of‐stars

Purpose

To investigate the properties of HYPR (HighlY constrained back PRojection) processing—the temporal fidelity and the improvements of spatial/temporal resolution—for contrast‐enhanced MR angiography in a pilot study of the lower extremities in healthy volunteers.

Materials and Methods

HYPR processing with a radial three‐dimensional (3D) stack‐of‐stars acquisition was investigated for contrast‐enhanced MR angiography of the lower extremities in 15 healthy volunteers. HYPR images were compared with control images acquired using a fast, multiphase, 2D Cartesian method to verify the temporal fidelity of HYPR. HYPR protocols were developed for achieving either a high frame update rate or a minimal slice thickness by adjusting the acquisition parameters. HYPR images were compared with images obtained using 3D TRICKS, a widely used protocol in dynamic 3D MRA.

Results

HYPR images showed good temporal agreement with 2D control images. In comparison with TRICKS, HYPR stack‐of‐stars demonstrated higher spatial and temporal resolution. High radial undersampling factors for each time frame were permitted, typically approximately 50 to 100 compared with fully sampled radial imaging.

Conclusion

In this feasibility study, HYPR processing has been demonstrated to improve the spatial or temporal resolution in peripheral CE‐MRA. J. Magn. Reson. Imaging 2009;29:917–923. © 2009 Wiley‐Liss, Inc.     

Fast oxygen-enhanced multislice imaging of the lung using parallel acquisition techniques.

The purpose of this study was to evaluate an optimized multislice acquisition technique for oxygen-enhanced MRI of the lung using slice-selective inversion and refocusing pulses in combination with parallel imaging. An inversion recovery HASTE sequence was implemented with respiratory triggering to perform imaging in end-expiration and with ECG triggering to avoid image acquisition during the systolic phase. Inversion pulses and the readout of echo trains could be interleaved to decrease acquisition time. The sequence was evaluated in 15 healthy volunteers, comparing three acquisition schemes: (1) acquisition of four slices without parallel imaging; (2) acquisition of four slices with parallel imaging; (3) acquisition of six slices with parallel imaging. These multislice acquisitions were repeated 80 times with alternating inhalation of room air and oxygen. The oxygen-induced signal increase showed no significant difference with and without parallel imaging. However, only with parallel imaging did the interleaved acquisition of six or more slices become possible, thus enabling a more complete anatomic coverage of the lung. The average required end-expiration time per repetition to acquire six slices could be significantly reduced from 4112 ms without to 2727 ms with parallel imaging. Total acquisition time varied between 8 and 13 min depending on the respiratory frequency.     

Estimation of k‐space trajectories in spiral MRI

For non‐Cartesian data acquisition in MRI, k‐space trajectory infidelity due to eddy current effects and other hardware imperfections will blur and distort the reconstructed images. Even with the shielded gradients and eddy current compensation techniques of current scanners, the deviation between the actual k‐space trajectory and the requested trajectory remains a major reason for image artifacts in non‐Cartesian MRI. It is often not practical to measure the k‐space trajectory for each imaging slice. It has been reported that better image quality is achieved in radial scanning by correcting anisotropic delays on different physical gradient axes. In this article the delay model is applied in spiral k‐space trajectory estimation to reduce image artifacts. Then a novel estimation method combining the anisotropic delay model and a simple convolution eddy current model further reduces the artifact level in spiral image reconstruction. The root mean square error and peak error in both phantom and in vivo images reconstructed using the estimated trajectories are reduced substantially compared to the results achieved by only tuning delays. After a one‐time calibration, it is thus possible to get an accurate estimate of the spiral trajectory and a high‐quality image reconstruction for an arbitrary scan plane. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Myocardial perfusion MRI with sliding‐window conjugate‐gradient HYPR

First‐pass perfusion MRI is a promising technique for detecting ischemic heart disease. However, the diagnostic value of the method is limited by the low spatial coverage, resolution, signal‐to‐noise ratio (SNR), and cardiac motion‐related image artifacts. In this study we investigated the feasibility of using a method that combines sliding window and CG‐HYPR methods (SW‐CG‐HYPR) to reduce the acquisition window for each slice while maintaining the temporal resolution of one frame per heartbeat in myocardial perfusion MRI. This method allows an increased number of slices, reduced motion artifacts, and preserves the relatively high SNR and spatial resolution of the “composite images.” Results from eight volunteers demonstrate the feasibility of SW‐CG‐HYPR for accelerated myocardial perfusion imaging with accurate signal intensity changes of left ventricle blood pool and myocardium. Using this method the acquisition time per cardiac cycle was reduced by a factor of 4 and the number of slices was increased from 3 to 8 as compared to the conventional technique. The SNR of the myocardium at peak enhancement with SW‐CG‐HYPR (13.83 ± 2.60) was significantly higher (P < 0.05) than the conventional turbo‐FLASH protocol (8.40 ± 1.62). Also, the spatial resolution of the myocardial perfection images was significantly improved. SW‐CG‐HYPR is a promising technique for myocardial perfusion MRI. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Compatible dual‐echo arteriovenography (CODEA) using an echo‐specific K‐space reordering scheme

An improved dual‐echo sequence magentic resonance (MR) imaging technique was developed to simultaneously acquire a time‐of‐flight MR angiogram (MRA) and a blood oxygenation level‐dependent MR venogram (MRV) in a single MR acquisition at 3 T. MRA and MRV require conflicting scan conditions (e.g., excitation RF profile, flip angle, and spatial presaturation pulse) for their optimal image quality. This conflict was not well counterbalanced or reconciled in previous methods reported for simultaneous acquisition of MRA and MRV. In our dual‐echo sequence method, an echo‐specific K‐space reordering scheme was used to uncouple the scan parameter requirements for MRA and MRV. The MRA and MRV vascular contrast was enhanced by maximally separating the K‐space center regions acquired for the MRA and MRV, and by adjusting and applying scan parameters compatible between the MRA and MRV. As a preliminary result, we were able to acquire a simultaneous dual‐echo MRA and MRV with image quality comparable to that of the conventional single‐echo MRA and MRV that were acquired separately at two different sessions. Furthermore, integrated with tilted optimized nonsaturating excitation and multiple overlapping thin‐slab acquisition techniques, our dual‐echo MRA and MRV provided seamless vascular continuity over a large coverage volume of the brain anatomy. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Free‐breathing myocardial perfusion MRI using SW‐CG‐HYPR and motion correction

First‐pass perfusion MRI is a promising technique to detect ischemic heart disease. Sliding window (SW) conjugate‐gradient (CG) highly constrained back‐projection reconstruction (HYPR) (SW‐CG‐HYPR) has been proposed to increase spatial coverage, spatial resolution, and SNR. However, this method is sensitive to respiratory motion and thus requires breath‐hold. This work presents a non‐model‐based motion correction method combined with SW‐CG‐HYPR to perform free‐breathing myocardial MR imaging. Simulation studies were first performed to show the effectiveness of the proposed motion correction method and its independence from the pattern of the respiratory motion. After that, in vivo studies were performed in six healthy volunteers. From all of the volunteer studies, the image quality score of free breathing perfusion images with motion correction (3.11 ± 0.34) is improved compared with that of images without motion correction (2.27 ± 0.32), and is comparable with that of successful breath‐hold images (3.12 ± 0.38). This result was further validated by a quantitative sharpness analysis. The left ventricle and myocardium signal changes in motion corrected free‐breathing perfusion images were closely correlated to those observed in breath‐hold images. The correlation coefficient is 0.9764 for myocardial signals. Bland–Altman analysis confirmed the agreement between the free‐breathing SW‐CG‐HYPR method with motion correction and the breath‐hold SW‐CG‐HYPR. This technique may allow myocardial perfusion MRI during free breathing. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Visualization of inert gas wash‐out during high‐frequency oscillatory ventilation using fluorine‐19 MRI

High‐frequency oscillatory ventilation is looked upon as a lung‐protective ventilation strategy. For a further clarification of the physical processes promoting gas transport, a visualization of gas flow and the distribution of ventilation are of considerable interest. Therefore, fluorine‐19 magnetic resonance imaging of the imaging gas octafluorocyclobutane (C₄F₈) during high‐frequency oscillatory ventilation was performed in five healthy pigs. For that, a mutually compatible ventilation‐imaging system was set up and transverse images were acquired every 5 sec using FLASH sequences on a 1.5 T scanner. Despite a drop in signal‐to‐noise ratio after the onset of high‐frequency oscillatory ventilation, for each pig, the four experiments could be analyzed. A mean wash‐out time (τ) at 5 Hz of 52.7 ± 18 sec and 125.9 ± 39 sec at 10 Hz, respectively, were found for regions of interest including the whole lung. This is in agreement with the clinical findings, in that wash‐out of respiratory gases is significantly prolonged for increased high‐frequency oscillatory ventilation frequencies. Our study could be a good starting‐point for a further optimization of high‐frequency oscillatory ventilation. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Accelerated cardiac perfusion imaging using k‐t SENSE with SENSE training

In k‐t sensitivity encoding (SENSE), MR data acquisition performed in parallel by multiple coils is accelerated by sparsely sampling the k‐space over time. The resulting aliasing is resolved by exploiting spatiotemporal correlations inherent in dynamic images of natural objects. In this article, a modified k‐t SENSE reconstruction approach is presented, which aims at improving the temporal fidelity of first‐pass, contrast‐enhanced myocardial perfusion images at high accelerations. The proposed technique is based on applying parallel imaging on the training data in order to increase their spatial resolution. At a net acceleration of 5.8 (k‐t factor = 8, training profiles = 11) accurate representations of dynamic signal‐intensities were achieved. The efficacy of this approach as well as limitations due to noise amplification were investigated in computer simulations and in vivo experiments. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Quantitative 19F imaging of nmol‐level F‐nucleotides/‐sides from 5‐FU with T2 mapping in mice at 9.4T

A unique acquisition method is proposed for quantitative, high‐sensitivity ¹⁹F MR spectroscopic imaging for the study of drug distribution aiming at nmol‐level metabolite information in mice. The use of fast spin echo (FSE) at 9.4T allowed us to obtain whole‐body images with minimal effect of magnetic susceptibility and to acquire several metabolite signals simultaneously by the method of interleaved multifrequency selection. Modified 2‐shot FSE was designed for simultaneous, high‐sensitivity ¹⁹F imaging and T₂ mapping. A time course study including all the main metabolites at 10‐minute resolution was attained with an oral dose of 1–2 mmol 5‐fluorouracil (5‐FU) (130–260 mg)/kg in mice. With acquisition parameters optimized for in vivo T₂ of 40 ms, images of F‐nucleotides/‐sides, effective anabolites of the anticancer drug 5‐FU, were obtained at the level of 200 nmol in the tumor for all the mice studied with a linear correlation (R = 0.96) between image intensity and the quantity determined in the excised tissue. The method exhibits potential capability of molecular imaging with a variety of ¹⁹F‐labeled compounds and drug evaluation. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.