Neil Woodhouse

Combined helium-3/proton magnetic resonance imaging measurement of ventilated lung volumes in smokers compared to never-smokers.

To use a combination of helium‐3 (3‐He) magnetic resonance imaging (MRI) and proton single‐shot fast spin echo (SSFSE) to compare ventilated lung volumes in groups of “healthy” smokers, smokers diagnosed with moderate chronic obstructive pulmonary disease (COPD), and never‐smokers.

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.

MRI of Helium-3 Gas in Healthy Lungs: Posture Related Variations of Alveolar Size

To probe the variation of alveolar size in healthy lung tissue as a function of posture using diffusion‐weighted helium‐3 hyperpolarized gas imaging.

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.

Ventricular mass index correlates with pulmonary artery pressure and predicts survival in suspected systemic sclerosis-associated pulmonary arterial hypertension

OBJECTIVE The ventricular mass index (VMI) has been proposed as a diagnostic tool for the assessment of patients with suspected pulmonary hypertension (PH). We hypothesized that in patients with SSc it may predict the presence or absence of PH. METHODS Details of all consecutive SSc patients undergoing MRI and right heart catheterization were collected prospectively. Subsequently, the VMI for all patients was calculated, and further baseline data were collected. RESULTS Data for 40 patients, 28 of whom were diagnosed with PH at rest (PH(REST)), were analysed. VMI correlated strongly with mean pulmonary artery pressure (mPAP; r = 0.79). Using a VMI threshold of 0.56, positive predictive value (PPV) for PH(REST) was 88% and negative predictive value (NPV) was 100%. Using a threshold of 0.7, PPV was found to be 100% and NPV 53%. Echocardiographically obtained tricuspid gradient (TG) also demonstrated a strong correlation with mPAP. Two-year survival in patients with VMI <0.7 and > or =0.7 was 91 and 43%, respectively (P < 0.001). CONCLUSION VMI correlates well with mPAP in patients with SSc and may have a role in non-invasively excluding clinically significant PH in breathless SSc patients in whom echocardiographic screening has failed. Further study in larger groups of patients is justified.

Assessment of hyperpolarized 3He lung MRI for regional evaluation of interventional therapy: A pilot study in pediatric cystic fibrosis

To determine whether regional changes in lung ventilation in a group of pediatric cystic fibrosis (CF) patients following a course of chest physiotherapy could be detected with 3He MRI.

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.

Finite‐difference simulations of 3He diffusion in 3D alveolar ducts: Comparison with the “cylinder model”

Time‐dependent measurements of 3He diffusion in the lung could provide an accurate method to quantify alveolar length scales and the progression of diseases such as emphysema. However, the apparent diffusion coefficient (ADC) presents a complex problem to model and solve analytically. Here, finite‐difference methods were used to simulate diffusion in 3D alveolar ducts. The results were compared to the only available analytical model—the “cylinder model”—from which it is possible to estimate the average radii of the alveolar ducts from in vivo data. The trend in data observed from simulations was found to agree well with the cylinder model. However, the cylinder model always overestimated the average radii of the simulated alveolar ducts. The simulations also demonstrated that the measurement of the longitudinal ADC (along the alveolar ducts) should be sensitive to early emphysematous changes, whereas the measured radii should be far less sensitive. Magn Reson Med 52:917–920, 2004.