Med Phys
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Comparative Study
Simultaneous segmentation and iterative registration method for computing ADC with reduced artifacts from DW-MRI.
Apparent diffusion coefficient (ADC), derived from diffusion-weighted magnetic resonance images (DW-MRI), measures the motion of water molecules in vivo and can be used to quantify tumor response to therapy. The accurate measurement of ADC can be adversely affected by organ motion and imaging artifacts. In this paper, the authors' goal was to develop an automated method for reducing artifacts and thereby improve the accuracy of ADC measurements in moving organs such as liver. ⋯ The authors developed a novel approach for reducing artifacts in ADC maps through simultaneous registration and segmentation of multiple b-value DW images. The authors' method explicitly employs a registration quality metric to align images. When compared to basic affine and no image registrations, the authors' approach produces registrations of greater accuracy with lowest artifact ratio and median standard deviation of the computed mean ADC values for a wide range of displacements.
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Most clinically deployed strategies for respiratory motion management in lung radiotherapy (e.g., gating and tracking) use external markers that serve as surrogates for tumor motion. However, typical lung phantoms used to validate these strategies are based on a rigid exterior and a rigid or a deformable-interior. Such designs do not adequately represent respiration because the thoracic anatomy deforms internally as well as externally. In order to create a closer approximation of respiratory motion, the authors describe the construction and experimental testing of an externally as well as internally deformable, programmable lung phantom. ⋯ The authors have developed a realistic externally and internally deformable, programmable lung phantom that will serve as a valuable tool for clinical and investigational motion management studies in thoracic and abdominal radiation therapies.
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Comparative Study
Ultrashort echo-time MRI versus CT for skull aberration correction in MR-guided transcranial focused ultrasound: In vitro comparison on human calvaria.
Transcranial magnetic resonance-guided focused ultrasound (TcMRgFUS) brain treatment systems compensate for skull-induced beam aberrations by adjusting the phase and amplitude of individual ultrasound transducer elements. These corrections are currently calculated based on a preacquired computed tomography (CT) scan of the patient's head. The purpose of the work presented here is to demonstrate the feasibility of using ultrashort echo-time magnetic resonance imaging (UTE MRI) instead of CT to calculate and apply aberration corrections on a clinical TcMRgFUS system. ⋯ The authors have demonstrated that transcranial focal heating can be significantly improved in vitro by using UTE MRI to compute skull-induced ultrasound aberration corrections. Their results suggest that UTE MRI could be used instead of CT to implement such corrections on current 0.7 MHz clinical TcMRgFUS devices. The MR image acquisition and segmentation procedure demonstrated here would add less than 15 min to a clinical MRgFUS treatment session.
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Clinical Trial
Cyst-based measurements for assessing lymphangioleiomyomatosis in computed tomography.
To investigate the efficacy of a new family of measurements made on individual pulmonary cysts extracted from computed tomography (CT) for assessing the severity of lymphangioleiomyomatosis (LAM). ⋯ The proposed family of CT-based cyst measurements have better correlation with spirometric measures than previously used density based CT measurements. They show potential as a sensitive tool for quantitatively assessing the severity of LAM.
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In radiation therapy of pancreatic cancer, tumor alignment prior to each treatment fraction is improved when intratumoral gold fiducial markers (from here onwards: markers), which are visible on computed tomography (CT) and cone beam CT, are used. Visibility of these markers on magnetic resonance imaging (MRI) might improve image registration between CT and magnetic resonance (MR) images for tumor delineation purposes. However, concomitant image artifacts induced by markers are undesirable. The extent of visibility and artifact size depend on MRI-sequence parameters. The authors' goal was to determine for various markers their potential to be visible and to generate artifacts, using measures that are independent of the MRI-sequence parameters. ⋯ Changes in T2 (∗) and ΔB0 are sequence-independent measures for potential visibility and artifact size, respectively. Improved visibility of markers correlates strongly to signal shift artifacts; therefore, marker choice will depend on the clinical purpose. When visibility of the markers is most important, markers that contain iron are optimal, preferably in a folded configuration. For artifact sensitive imaging, small ironless markers are best, preferably in a stretched configuration.