E.E. de Lange

Merging parametric active contours within homogeneous image regions for MRI-based lung segmentation

Inhaled hyperpolarized helium-3 (/sup 3/He) gas is a new magnetic resonance (MR) contrast agent that is being used to study lung functionality. To evaluate the total lung ventilation from the hyperpolarized /sup 3/He MR images, it is necessary to segment the lung cavities. This is difficult to accomplish using only the hyperpolarized /sup 3/He MR images, so traditional proton (/sup 1/H) MR images are frequently obtained concurrent with the hyperpolarized /sup 3/He MR examination. Segmentation of the lung cavities from traditional proton (/sup 1/H) MRI is a necessary first step in the analysis of hyperpolarized /sup 3/He MR images. In this paper, we develop an active contour model that provides a smooth boundary and accurately captures the high curvature features of the lung cavities from the /sup 1/H MR images. This segmentation method is the first parametric active contour model that facilitates straightforward merging of multiple contours. The proposed method of merging computes an external force field that is based on the solution of partial differential equations with boundary condition defined by the initial positions of the evolving contours. A theoretical connection with fluid flow in porous media and the proposed force field is established. Then by using the properties of fluid flow we prove that the proposed method indeed achieves merging and the contours stop at the object boundary as well. Experimental results involving merging in synthetic images are provided. The segmentation technique has been employed in lung /sup 1/H MR imaging for segmenting the total lung air space. This technology plays a key role in computing the functional air space from MR images that use hyperpolarized /sup 3/He gas as a contrast agent.

MR grid-tagging using hyperpolarized helium-3 for regional quantitative assessment of pulmonary biomechanics and ventilation.

A new technique is demonstrated in six healthy human subjects that combines grid‐tagging and hyperpolarized helium‐3 MRI to assess regional lung biomechanical function and quantitative ventilation. 2D grid‐tagging, achieved by applying sinc‐modulated RF‐pulse trains along the frequency‐ and phase‐encoding directions, was followed by a multislice fast low‐angle shot (FLASH)‐based acquisition at inspiration and expiration. The displacement vectors, first and second principal strains, and quantitative ventilation were computed, and mean values were calculated for the upper, middle, and lower lung regions. Displacements in the lower region were significantly greater than those in either the middle or upper region (P < 0.005), while there were no significant differences between the three regions for the two principal strains and quantitative ventilation (P = 0.11–0.92). Variations in principal strains and ventilation were greater between subjects than between lung zones within individual subjects. This technique has the potential to provide insight into regional biomechanical alterations of lung function in a variety of lung diseases. Magn Reson Med 58:373–380, 2007.

MRI ventilation analysis by merging parametric active contours

A novel technique that combines MR imaging of hyperpolarized helium gas and conventional MR imaging facilitates, high resolution imaging of lung functionality for the first time. We put forth a segmentation method for measuring the total lung air space and a classification approach to computing the functional air space. For segmentation, we introduce a parametric active contour that allows automated merging of multiple contours. The active contour technique uses gradient vector flow modified and strengthened by a boundary condition that inhibits contour crossover. The active contour approach is computationally inexpensive and is independent of initial contour placement. For classification of the functional lung air space in the helium images, a fuzzy c-means technique is applied. The classification results, in conjunction with the segmentation, allow the analysis of ventilation. The resultant biomedical image analysis tool can used in determining the efficacy of certain respiratory treatments.

RM con gases hiperpolarizados: Nuevas perspectivas en el estudio de enfermedades pulmonares

Hyperpolarized (HP) gases are a new class of contrast agents that permit to obtain high temporal and spatial resolution magnetic resonance images (MRI) of the lung airspaces. HP gas MRI has become important research tool not only for morphological and functional evaluation of normal pulmonary physiology but also for regional quantification of pathologic changes occurring in several lung diseases. The purpose of this work is to provide an introduction to MRI using HP noble gases, describing both the basic principles of the technique and the new information about lung disease provided by clinical studies with this method. The applications of the technique in normal subjects, smoking related lung disease, asthma, and cystic fibrosis are reviewed.

Renal Artery Stenosis and Accessory Renal Arteries: Accuracy of Detection and Visualization With Gadolinium-Enhanced Breath-Hold MR Angiography

PURPOSE To determine the accuracy of gadolinium-enhanced breath-hold magnetic resonance (MR) angiography in the diagnosis of renal artery stenosis and visualization of accessory renal arteries. MATERIALS AND METHODS Forty-four patients suspected of having renal artery stenosis and 10 potential kidney donors, all of whom were scheduled to undergo elective intraarterial digital subtraction angiography (DSA), were studied. Three-dimensional gradient-echo gadolinium-enhanced MR angiography was performed at 1.5 T with the following parameters: repetition time, 13.5 msec; echo time, 3.5 msec; flip angle, 60 degrees; 195 x 512 matrix; 400-mm field of view; and 6-cm imaging volume consisting of 15 4-mm-thick partitions reconstructed every 2 mm. Gadopentetate dimeglumine (30 mL) was injected with a power injector. MR angiograms were assessed before the standard of reference, intraarterial DSA, was performed. RESULTS Four MR angiograms were not evaluable because of poor image quality. MR angiography enabled visualization of all but one of the 121 arteries. In four small accessory arteries, a stenosis could not be excluded owing to inadequate spatial resolution. MR angiography enabled the correct diagnosis in 30 of the 31 arteries with a grade 2 (50%-99%) stenosis and in seven of the 10 occluded arteries. Sensitivity and specificity for correct identification of a grade 2 stenosis were 97% and 92%, respectively. CONCLUSION Gadolinium-enhanced MR angiography is an accurate, minimally invasive method for detecting renal artery stenosis and is reliable for visualizing accessory renal arteries.

PULMONARY KINEMATICS FROM HYPERPOLARIZED HELIUM-3 TAGGED MAGNETIC RESONANCE IMAGING

Recent innovations in hyperpolarized helium-3 magnetic resonance imaging (MRI) include the employment of MR tagging techniques for assessment of pulmonary deformation. Historically, such tagging methods have been successfully applied to cardiac research inspiring the development of computational techniques for the quantitative analysis of myocardial deformation. We present related research which concerns the calculation of kinematic quantities, such as displacement and strain, in the lung. Utilizing the high contrast tag lines as landmarks in the images and a recently developed fast n-D B-spline approximation algorithm, we fit a parametric object to the sparse tag line data to smoothly interpolate the underlying deformation field and, subsequently, extract lung kinematic information. We present results from a single human volunteer

SU-FF-J-24: Functional Planning for Tomotherapy-Based Stereotactic Body Radiotherapy (SBRT) for Peripheral Lung Tumors

Purpose: To investigate the impact of incorporating hyperpolarized heliume‐3 (HP He‐3) MRI ventilation images to Tomotherapy‐based stereotactic body radiation therapy(SBRT) planning for peripheral lungtumors.Method and Materials:CT and HP He‐3 MRI ventilation images of 6 subjects were co‐registered for segmentation. Highly functional lungs (HFL) were defined as the 70‐percentile hyperventilation lungs and less functional lungs (LFL) were subsequently calculated. A cylinder‐shaped artificial object was created in peripheral lungs to mimic planning‐target‐volume (PTV). Two Tomotherapy‐based IMRT plans, a anatomical plan (Plan 1) and a functional plan (Plan 2), were designed with SBRT‐type prescription (60Gy in 5 fractions) and normal tissue constrains. The following dosimetric parameters were compared between two plans: total lung V20 (TLV20), highly functional lungs V20 (HFLV20), less functional lungs V20 (LFLV20), mean total lungdose (MTLD), mean highly functional lungdose (MHFLD), mean less functional lungdose (MLFLD), max dose to organs at risk (OARs) and conformality index (CI). Results: Compared to Plane 1, Plan 2 significantly reduced HFLV20 (median reduction 2.1%, range 0.7–2.9%, p‐value=0.031), TLV20 (median reduction 1.6%, range 0.5–2.1%, p‐value=0.031), MHFLD (median reduction 0.8Gy, range 0.4–1.0Gy, p‐value=0.031), and MTLD (median reduction 0.7Gy, range 0.1–1.0Gy, p‐value=0.031). There was no significant difference in LFLV20 and MLFLD (p‐value is 0.438 and 0.156 respectively). Dose constrains for OARs were satisfied in all plans and max doses to OARs were not significantly changed in Plan 2 (p‐values range: 0.063–0.563). CI was generally reduced in Plan 2 (median reduction 0.02) but the difference is insignificant (p‐value=0.125). Conclusions: The incorporation of HP He‐3 MRI ventilation information to the Tomotherapy‐based SBRT planning for peripheral lungcancer improved the sparring of radiation dose to highly functional lungs and can potentially preserve more highly functional lungs. Conflict of Interest: Dr. Paul W. Read serves as a consultant for Tomotherapy Inc.

Point-set registration of tagged HE-3 images using a structurally-based Jensen-Shannon divergence measure within a deterministic annealing framework

Helium-3 tagged magnetic resonance imaging has demonstrated potential for calculating pulmonary deformation from medical imagery. Such measurements are useful for determining the biomechanical properties of the lung. Unfortunately, the relative facility of visually tracking deformation via the high contrast tag lines has not transferred readily to the algorithmic domain of automatically establishing tag-line correspondences. We proffer a solution to this dilemma by translating the problem into a unique point-set registration scenario. Not only does this permit capitalizing on certain spectral aspects of tagged MRI but registration can be performed within a deterministic annealing framework for decreased susceptibility to local minima.