Quantitative assessment of emphysema using hyperpolarized 3He magnetic resonance imaging.

In this experiment, Sprague-Dawley rats with elastase-induced emphysema were imaged using hyperpolarized (3)He MRI. Regional fractional ventilation r, the fraction of gas replaced with a single tidal breath, was calculated from a series of images in a wash-in study of hyperpolarized gas. We compared the regional fractional ventilation in these emphysematous rats to the regional fractional ventilations we calculated from a previous baseline study in healthy Sprague-Dawley rats. We found that there were differences in the maps of fractional ventilation and its associated frequency distribution between the healthy and emphysematous rat lungs. Fractional ventilation tended to be much lower in emphysematous rats than in normal rats. With this information, we can use data on fractional ventilation to regionally distinguish between healthy and emphysematous portions of the lung. The successful implementation of such a technique on a rat model could lead to work toward the future implementation of this technique in human patients.     

Comparison of myocardial perfusion estimates from dynamic contrast‐enhanced magnetic resonance imaging with four quantitative analysis methods

Dynamic contrast‐enhanced MRI has been used to quantify myocardial perfusion in recent years. Published results have varied widely, possibly depending on the method used to analyze the dynamic perfusion data. Here, four quantitative analysis methods (two‐compartment modeling, Fermi function modeling, model‐independent analysis, and Patlak plot analysis) were implemented and compared for quantifying myocardial perfusion. Dynamic contrast‐enhanced MRI data were acquired in 20 human subjects at rest with low‐dose (0.019 ± 0.005 mmol/kg) bolus injections of gadolinium. Fourteen of these subjects were also imaged at adenosine stress (0.021 ± 0.005 mmol/kg). Aggregate rest perfusion estimates were not significantly different between all four analysis methods. At stress, perfusion estimates were not significantly different between two‐compartment modeling, model‐independent analysis, and Patlak plot analysis. Stress estimates from the Fermi model were significantly higher (～20%) than the other three methods. Myocardial perfusion reserve values were not significantly different between all four methods. Model‐independent analysis resulted in the lowest model curve‐fit errors. When more than just the first pass of data was analyzed, perfusion estimates from two‐compartment modeling and model‐independent analysis did not change significantly, unlike results from Fermi function modeling. Magn Reson Med 64:125–137, 2010. © 2010 Wiley‐Liss, Inc.     

Non‐contrast‐enhanced perfusion and ventilation assessment of the human lung by means of fourier decomposition in proton MRI

Assessment of regional lung perfusion and ventilation has significant clinical value for the diagnosis and follow‐up of pulmonary diseases. In this work a new method of non‐contrast‐enhanced functional lung MRI (not dependent on intravenous or inhalative contrast agents) is proposed. A two‐dimensional (2D) true fast imaging with steady precession (TrueFISP) pulse sequence (TR/TE = 1.9 ms/0.8 ms, acquisition time [TA] = 112 ms/image) was implemented on a 1.5T whole‐body MR scanner. The imaging protocol comprised sets of 198 lung images acquired with an imaging rate of 3.33 images/s in coronal and sagittal view. No electrocardiogram (ECG) or respiratory triggering was used. A nonrigid image registration algorithm was applied to compensate for respiratory motion. Rapid data acquisition allowed observing intensity changes in corresponding lung areas with respect to the cardiac and respiratory frequencies. After a Fourier analysis along the time domain, two spectral lines corresponding to both frequencies were used to calculate the perfusion‐ and ventilation‐weighted images. The described method was applied in preliminary studies on volunteers and patients showing clinical relevance to obtain non‐contrast‐enhanced perfusion and ventilation data. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Quantification of pulmonary microcirculation by dynamic contrast‐enhanced magnetic resonance imaging: Comparison of four regularization methods

Tissue microcirculation can be quantified by a deconvolution analysis of concentration–time curves measured by dynamic contrast‐enhanced magnetic resonance imaging. However, deconvolution is an ill‐posed problem, which requires regularization of the solutions. In this work, four algebraic deconvolution/regularization methods were evaluated: truncated singular value decomposition and generalized Tikhonov regularization (GTR) in combination with the L‐curve criterion, a modified LCC (GTR‐MLCC), and a response function model that takes a‐priori knowledge into account. To this end, dynamic contrast‐enhanced magnetic resonance imaging data sets were simulated by an established physiologically reference model for different signal‐to‐noise ratios and measured on a 1.5‐T system in the lung of 10 healthy volunteers and 20 patients. Analysis of both the simulated and measured dynamic contrast‐enhanced magnetic resonance imaging datasets revealed that GTR in combination with the L‐curve criterion does not yield reliable and clinically useful results. The three other deconvolution/regularization algorithms resulted in almost identical microcirculatory parameter estimates for signal‐to‐noise ratios > 10. At low signal‐to‐noise ratios levels (<10) typically occurring in pathological lung regions, GTR in combination with a modified L‐curve criterion approximates the true response function much more accurately than truncated singular value decomposition and GTR in combination with response function model with a difference in accuracy of up to 76%. In conclusion, GTR in combination with a modified L‐curve criterion is recommended for the deconvolution of dynamic contrast‐enhanced magnetic resonance imaging curves measured in the lung parenchyma of patients with highly heterogeneous signal‐to‐noise ratios. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

Prostate cancer detection with 3 T MRI: Comparison of diffusion‐weighted imaging and dynamic contrast‐enhanced MRI in combination with T2‐weighted imaging

Purpose:

To evaluate the diagnostic ability of diffusion‐weighted imaging (DWI) and dynamic contrast‐enhanced imaging (DCEI) in combination with T2‐weighted imaging (T2WI) for the detection of prostate cancer using 3 T magnetic resonance imaging (MRI) with a phased‐array body coil.

Materials and Methods:

Fifty‐three patients with elevated serum levels of prostate‐specific antigen (PSA) were evaluated by T2WI, DWI, and DCEI prior to needle biopsy. The obtained data from T2WI alone (protocol A), a combination of T2WI and DWI (protocol B), a combination T2WI and DCEI (protocol C), and a combination of T2WI plus DWI and DCEI (protocol D) were subjected to receiver operating characteristic (ROC) curve analysis.

Results:

The sensitivity, specificity, accuracy, and area under the ROC curve (Az) for region‐based analysis were: 61%, 91%, 84%, and 0.8415, respectively, in protocol A; 76%, 94%, 90%, and 0.8931, respectively, in protocol B; 77%, 93%, 89%, and 0.8655, respectively, in protocol C; and 81%, 96%, 92%, and 0.8968, respectively in protocol D. ROC analysis revealed significant differences between protocols A and B (P = 0.0008) and between protocols A and D (P = 0.0004).

Conclusion:

In patients with elevated PSA levels the combination of T2WI, DWI, DCEI using 3 T MRI may be a reasonable approach for the detection of prostate cancer. J. Magn. Reson. Imaging 2010;31:625–631. © 2010 Wiley‐Liss, Inc.     

Nuclear magnetic resonance imaging of airways in humans with use of hyperpolarized 3He

The nuclear spin polarization of noble gases can be enhanced strongly by laser optical pumping followed by electron-nuclear polarization transfer. Direct optical pumping of metastable ³He atoms has been shown to produce enormous polarization on the order of 0.4–0.6. This is about 10⁵ times larger than the polarization of water protons at thermal equilibrium used in conventional MRI. We demonstrate that hyper-polarized ³He gas can be applied to nuclear magnetic resonance imaging of organs with air-filled spaces in humans. In vivo ³He MR experiments were performed in a whole-body MR scanner with a superconducting magnet ramped down to 0.8 T. Anatomical details of the upper respiratory tract and of the lungs of a volunteer were visualized with the FLASH technique demonstrating the potential of the method for fast imaging of airways in the human body and for pulmonary ventilation studies.     

High‐resolution magnetic resonance colonography and dynamic contrast‐enhanced magnetic resonance imaging in a murine model of colitis

Inflammatory bowel disease, including ulcerative colitis, is characterized by persistent or recurrent inflammation and can progress to colon cancer. Colitis is difficult to detect and monitor noninvasively. The goal of this work was to develop a preclinical imaging method for evaluating colitis. Herein, we report improved MRI methods for detecting and characterizing colitis noninvasively in mice, using high‐resolution in vivo MR images and dynamic contrast‐enhanced MRI studies, which were confirmed by histologic studies in a murine model of colitis. C57Bl6/J male mice were treated with 2.5% dextran sulfate sodium in their drinking water for 5 days to induce colitis. MR images were acquired using a 9.4‐T Bruker scanner from 5–25 days following dextran sulfate sodium treatment. In dynamic contrast‐enhanced MRI studies, Gd uptake (K^trans) and its distribution (v_e) were measured in muscle and normal and inflamed colons after administering Gd‐diethyltriaminepentaacetic acid (Gd‐DTPA). T₂‐weighted MR images distinguished normal colon from diffusely thickened colonic wall occurring in colitis (P <0.0005) and correlated with histologic features. Values of K^trans and v_e obtained from dynamic contrast‐enhanced MRI were also significantly different in inflamed colons compared to normal colon (P < 0.0005). The results demonstrate that both T₂‐weighted anatomic imaging and quantitative analysis of dynamic contrast‐enhanced MRI data can successfully distinguish colitis from normal colon in mice. Magn Reson Med 63:922–929, 2010. © 2010 Wiley‐Liss, Inc.     

Determination of regional VA/Q by hyperpolarized 3He MRI.

Alveolar ventilation/perfusion ratio (VA/Q) is a key parameter in functional imaging of the lung. Herein, regional VA/Q was calculated from regional values of alveolar partial pressure of oxygen (PAO2) measured by hyperpolarized 3He gas MRI (HP 3He MRI). Yorkshire pigs (n = 7, mean weight = 25 kg) were paralyzed and maintained under isoflurane anesthesia. Animals were placed into a birdcage coil, then transferred to the bore of a 1.5 T MRI unit. Prior to imaging, animals were manually ventilated with room air for 5 min, then a 3He gas mixture was administered during breathhold and imaging performed. PAO2 was measured based on the decay rate of 3He signal. Subjects' blood gas concentrations were measured and these values and PAO2 values entered into a system of four equations with four unknowns. Calculated VA/Q values were analyzed by preparing frequency distributions for the entire lung and compared to VA/Q frequency distributions previously established in the literature as normal using other diagnostic techniques. Distributions were consistent with those in the literature, indicating that HP 3He MRI may be an accurate, quantitative, noninvasive, and nonradioactive method for acquiring VA/Q for small regions of the lung.     

Motion compensated generalized reconstruction for free‐breathing dynamic contrast‐enhanced MRI

The analysis of abdominal and thoracic dynamic contrast‐enhanced MRI is often impaired by artifacts and misregistration caused by physiological motion. Breath‐hold is too short to cover long acquisitions. A novel multipurpose reconstruction technique, entitled dynamic contrast‐enhanced generalized reconstruction by inversion of coupled systems, is presented. It performs respiratory motion compensation in terms of both motion artefact correction and registration. It comprises motion modeling and contrast‐change modeling. The method feeds on physiological signals and x‐f space properties of dynamic series to invert a coupled system of linear equations. The unknowns solved for represent the parameters for a linear nonrigid motion model and the parameters for a linear contrast‐change model based on B‐splines. Performance is demonstrated on myocardial perfusion imaging, on six simulated data sets and six clinical exams. The main purpose consists in removing motion‐induced errors from time–intensity curves, thus improving curve analysis and postprocessing in general. This method alleviates postprocessing difficulties in dynamic contrast‐enhanced MRI and opens new possibilities for dynamic contrast‐enhanced MRI analysis. Magn Reson Med, 2011. © 2010 Wiley‐Liss, Inc.