Stan Fichele

Dynamic radial projection MRI of inhaled hyperpolarized 3He gas.

A radial projection sliding‐window sequence has been developed for imaging the rapid flow of 3He gas in human lungs. The short echo time (TE) of the radial sequence lends itself to fast repetition times, and thus allows a rapid update in the image when it is reconstructed with a sliding window. Oversampling in the radial direction combined with angular undersampling can further reduce the time needed to acquire a complete image data set, without significantly compromising spatial resolution. Controlled flow phantom experiments using hyperpolarized 3He gas exemplify the temporal resolution of the method. In vivo studies on three healthy volunteers, one patient with chronic obstructive pulmonary disease (COPD), and one patient with hemiparalysis of the right diaphragm demonstrate that it is possible to accurately resolve the passage of gas down the trachea and bronchi and into the peripheral lung. Magn Reson Med 49:991–997, 2003.

3D volume-localized pO2 measurement in the human lung with 3He MRI

A method for 3D volume‐localized quantification of pO2 in the lungs is presented that uses repetitive frame 3D gradient‐echo imaging of 3He. The method was demonstrated by experiments on 3He phantoms containing known concentrations of O2 and in vivo on a group of three healthy human volunteers. The results were compared with those obtained by equivalent 2D thin‐slice and 2D projection methodologies, and were found to be consistent with published results from the 2D projection methodologies (pO2 = 0.09–0.18 bar). Studies performed on the same subject, on three separate occasions, demonstrated a repeatability of pO2 measurement to within 14% using the 3D technique. Experimental differences between the 2D and 3D methods were substantiated with theoretical and numerical analyses of the signal decay, which took into account the effects of out‐of‐slice diffusion as a source of error in the thin‐slice 2D experiments. It is shown that the 2D thin‐slice technique systematically underestimates pO2 when there is significant gas diffusion (factor of 4 underestimate for D = 0.9 cm2s−1 representative of free 3He in air). Magn Reson Med 53:1055–1064, 2005.

Quantitative analysis of regional airways obstruction using dynamic hyperpolarized 3He MRI—Preliminary results in children with cystic fibrosis

To investigate regional airways obstruction in patients with cystic fibrosis (CF) with quantitative analysis of dynamic hyperpolarized (HP) 3He MRI.

Comparison between 2D and 3D gradient-echo sequences for MRI of human lung ventilation with hyperpolarized 3He.

Images of hyperpolarized 3He were acquired during breath‐hold in four healthy volunteers with the use of an optimized 3D gradient‐echo sequence. The images were compared with existing 2D gradient‐echo methods. The average SNR from a 13‐mm‐thick slice in the peripheral lung was 1.4 times greater with 3D. In the airways the average SNR was 1.7 times greater with 3D. The higher SNR of 3D was particularly evident when regions of unimpeded gas diffusion, such as the major airways, were imaged with thin slices. This is because diffusion dephasing due to the slice‐encoding gradient is minimized with a 3D sequence. The in vivo experimental findings were substantiated with experiments on phantoms of free gas, which showed more than four times the SNR with 3D compared to 2D. Theoretical simulations of the 2D and 3D k‐space filters were also performed to predict the SNR and spatial resolution observed in the experimental images. Magn Reson Med 52:673–678, 2004.

Rapid lung volumetry using ultrafast dynamic magnetic resonance imaging during forced vital capacity maneuver: correlation with spirometry

Introduction: Dynamic magnetic resonance imaging (MRI) has the potential for rapid noninvasive evaluation of changes in lung volume. The aim of this study was to perform rapid lung volumetry using ultrafast dynamic MRI to capture a forced vital capacity (FVC) maneuver. Materials and methods: Nine healthy volunteers underwent 2-dimensional spoiled gradient echo imaging in coronal and sagittal planes during FVC maneuvers. An elliptical model of the axial cross section of the lungs was used to generate rapid volume-time curves. Spirometric indices were correlated with MR volumetry findings. Results: Total lung volume calculated from static MRI correlated well with the dynamic MR scans (r = 0.83; P < 0.01). Spirometric indices (first second of forced expiration and FVC) calculated from our MR volumetry technique correlated well with conventional spirometry (P < 0.01). Conclusion: The technique provides a means of sampling lung volume change during the rapid subsecond movements that take place during a FVC maneuver.

Assessment and compensation of susceptibility artifacts in gradient echo MRI of hyperpolarized 3He gas

The effects of macroscopic background field gradients upon 2D gradient echo images of inhaled 3He in the human lung were investigated at 1.5 T. Effective compensation of in‐slice signal loss in 3He gradient echo images was then demonstrated using a multiple acquisition interleaved single gradient echo sequence. This method restores signal dephasing through a combination of separate images acquired with different slice refocusing gradients. In vivo imaging of volunteers with the sequence shows substantial restoration of signal at the lung periphery and close to blood vessels. The technique presented may be useful when using 3He MRI for volumetric measurements of lung ventilation and in studies using 3He combined with intravenous contrast as a means of assessing lung ventilation/perfusion (V/Q). Magn Reson Med 50:417–422, 2003.