Ashley G. Anderson

Endoscopic optic nerve decompression for the treatment of traumatic optic nerve neuropathy.

Objective: We aimed to investigate the efficacy of endoscopic optic nerve decompression in patients with traumatic optic neuropathy. Methods: We performed a retrospective analysis of 46 patients with traumatic optic neuropathy in the Shanghai Eye, Ear, Nose and Throat Hospital between March 2002 and September 2005. All patients were first treated with methylprednisolone for 6 days. Forty-four patients (46 eyes) that did not improve with methylprednisolone treatment were offered endoscopic optic nerve decompression. Results: In 38 eyes with no light perception vision preoperatively, 21 eyes (45.6%) had improvement in visual acuity. These patients had postoperative light perception in 17 eyes, hand movement in 3 eyes and 60/200 in 1 eye. Four of 5 eyes with light perception preoperatively had postoperative vision for hand movement in 2 eyes, finger counting in 1 eye and 20/200 in 1 eye. For 3 eyes with preoperative visual acuity of hand movement, the postoperative visual acuities were 60/200, 60/200 and 120/200. Neither worsening of vision nor major complications was encountered in our series. Conclusions: We conclude that endoscopic optic nerve decompression in experienced surgeons’ hands can improve visual acuity in traumatic optic nerve neuropathy with minimal morbidity. Our results also demonstrate that even patients initially without light perception may benefit from optic nerve decompression.

Adaptive retrospective correction of motion artifacts in cranial MRI with multicoil three-dimensional radial acquisitions: Adaptive 3D Motion Correction

Despite reduction in imaging times through improved hardware and rapid acquisition schemes, motion artifacts can compromise image quality in magnetic resonance imaging, especially in three‐dimensional imaging with its prolonged scan durations. Direct extension of most state‐of‐the‐art two‐dimensional rigid body motion compensation techniques to the three‐dimensional case is often challenging or impractical due to a significant increase in sampling requirements. This article introduces a novel motion correction technique that is capable of restoring image quality in motion corrupted two‐dimensional and three‐dimensional radial acquisitions without a priori assumptions about when motion occurs. The navigating properties of radial acquisitions—corroborated by multiple receiver coils—are exploited to detect actual instances of motion. Pseudorandom projection ordering provides flexibility of reconstructing navigator images from the obtained motion‐free variable‐width subsets for subsequent estimation of rigid body motion parameters by coregistration. The proposed approach does not require any additional navigators or external motion estimation schemes. The capabilities and limitations of the method are described and demonstrated through simulations and representative volunteer cranial acquisitions. Magn Reson Med 69:1094–1103, 2013.

Respiratory‐induced venous blood flow effects using flexible retrospective double‐gating

To demonstrate a novel velocity sensitive acquisition and retrospective cardiorespiratory double‐gated reconstruction scheme to examine respiratory effect on venous blood flow in healthy volunteers.

Respiratory effects on phase contrast imaging of the jugular vein.

An analysis of the effect of respiratory function on MR flow measures of the internal jugular vein (IJV) is presented. A novel 2D radial acquisition and reconstruction method allows for retrospective gating to both the cardiac and respiratory cycle. In-vivo scans of human volunteers verify the efficacy of the algorithm, showing increased IJV flow during inspiration and decreased flow during expiration for each cardiac time frame.

3D respiratory resolved phase contrast imaging of the aorta

Background Respiratory motion compensation is essential for reproducible and robust cardiovascular MRI. Traditionally, breathholds or prospective gating by bellows or navigator signals limit data acquisition to the quiescent phase of respiration [1]. These approaches do not capture any variations of blood flow over the respiratory cycle, yet respiration has been shown to significantly affect flow in the great vessels [2]. The purpose of this pilot study was to adapt a 3D radially undersampled PC MR sequence (PC VIPR [3,4]) for use with our retrospective dual-gated (cardiac and respiratory) reconstruction to evaluate respiratory effects on net flow and cardiac flow waveforms.

Retrospective registration-based MRI motion correction with interleaved radial trajectories

Despite reduction in imaging times through improved hardware and rapid acquisition schemes, motion artifacts can compromise image quality in magnetic resonance imaging (MRI). This is especially true for 3D imaging, where scan durations are prolonged and the assumptions of most state-of-the-art 2D rigid body motion compensation techniques break down. This paper introduces a novel motion correction technique that is capable of restoring image quality in motion corrupted 2D/3D radial acquisitions. First, the available set of projections is subdivided into motion-free subsets of data using a novel center of mass based motion detection approach. For acquisitions with multiple receiver coils, both rotational and translational motion are detected. Next, the motion parameters are estimated on a sub-pixel level by co-registration of the data subsets. This approach does not require any additional navigators or external motion estimation schemes. The capabilities and limitations of the method are described and demonstrated on an application in cranial imaging.

Technique for retrospective respiratory and cardiac-gated phase contrast flow measurements

Summary A technique for evaluation of respiratory impact on cardiac-gated phase contrast flow acquisitions is proposed. An example study was performed showing the effect of active respiration on CSF flow through the spinal canal. Background The effect of the respiratory cycle on flow is well documented for cerebrospinal venous return [1] and CSF flow [2]. However, cranial phase contrast (PC) MR flow measurements neglect the influence of respiration. Breath-held acquisitions are possible, but mask physiological flow changes that occur during active respiration. Here we demonstrate a technique to evaluate the effects of active respiration on CSF flow measurements throughout the cardiac cycle for 2 respiration states. Methods Our approach relies on pseudo-random sampling of radial projections, which allows reconstruction of subsets with little artifact due to even filling of k-space (Fig. 1a). Cardiac triggers and respiratory position are recorded throughout the acquisition. Each projection then has a corresponding cardiac position (time since last trigger) and respiratory position. In the current implementation, all projections are sorted into 2 respiratory phases based on the median respiratory position. Each phase corresponds to the plateau surrounding endinspiration or -expiration. Each respiratory phase is represented by a cardiac gated image series that is reconstructed using a temporal filtering similar to view sharing in Cartesian acquisitions [3]. Three volunteers were scanned on a clinical 3T system with 2D radial PC acquisitions [4] between the C2 and C3 vertebrae: TR/TE = 9.4/6.1 ms, tip = 5°, resolution = 0.9x0.9x5 mm, and Venc = 8cm/s. Data were acquired during inspiration and expiration breath holds (1500 projections, 30 s), and during regular free and deep breathing (8000 projections, 2:32 min). Triggering was accomplished with pulse oximeter and bellow signals. Results Fig. 2 shows the resulting flow waveforms acquired during deep breathing for two volunteers. Though the waveforms show variation, the trend of increased flow during inspiration holds in both examples. Average forward (Qf), reverse (Qr), and net (Qnet) flow were calculated for both phases in the free breathing scans. For the inspiration phase, these values were: Qf = 3.06, Qr = 1.53, and Qnet = 1.53 ml/min. For the bin surrounding end-expiration, these values were: Qf = 2.53, Qr = 2.02, Qnet = 0.51 ml/min. Conclusions