Echo Slices Research Articles

Interrupted-Sampling Repeater Jamming Countermeasure Based on Intrapulse Frequency–Coded Joint Frequency Modulation Slope Agile Waveform

Interrupted-sampling repeater jamming (ISRJ) is widely used in the field of electronic countermeasures, and can severely affect radar detection. Therefore, the problem of ISRJ suppression is a compelling task. In this paper, we propose an ISRJ suppression method based on an intrapulse frequency-coded joint frequency modulation (FM) slope agile waveform. The intrapulse frequency-coded joint FM slope agile waveform is first designed. The delay inserted between subpulses makes the waveform easy to implement in engineering, and the ambiguity function diagram of the waveform approximates the ideal thumbtack type. Next, the echo slices are classified in the fractional domain utilizing the discontinuity of ISRJ and the focusing property of fractional Fourier transform for chirp signals. Then, the target and interference in the interfered echo slices are reconstructed by compressed sensing, and a time-domain filter is constructed based on interference-free echo slices. Finally, the echo signal after interference suppression is further filtered in the time domain to degrade range sidelobes. Simulation results show that the proposed method can effectively suppress three typical types of ISRJ. Moreover, the probability of target detection after interference suppression exceeds 90% when the jamming-to-signal ratio equals 50 dB.

Left Atrial Appendage Analysis from Echocardiographic Images: Relevance in Left Atrial Appendage Occlusion

Abstract Atrial fibrillation, a prevalent cardiac arrhythmia, disrupts the normal path of electrical signals within the heart. To address this issue, the left atrial appendage closure is often considered. This involves using a closure instrument named the Watchman to obstruct the left atrial appendage (LAA) ostium. The wide variety of LAA shapes, sizes, and forms in individuals makes selecting the correct Watchman size crucial. This study first isolates the LAA from echocardiographic images and then recommends the appropriate Watchman size. The 3-D echocardiographic images used in this study are from 32 male and female patients who underwent successful LAA closure at Kings College Hospital London over two years. For each patient, there are 208 cardiac echo slices in the imaging mode. This study presents an image processing-based model to separate LAA regions and extract relevant features. These features are then inputted into a classification platform in which a neural network determines the suitable Watchman size. The average and mode Hausdorff distances, calculated between the proposed method and the traditional manual calculation for the 501 analyzed LAA images, are approximately 0.2467 and 0.0587, respectively. Because of limited data, a 10-fold cross-validation was used to assess the classifier, yielding an accuracy of 74.07 %. The proposed model effectively isolated the LAA from the corresponding slices of the 3-D echocardiographic images. However, the classifier’s accuracy is not ideal because of insufficient data, which could be improved by expanding the database. This research’s outcomes could aid physicians in selecting the proper Watchman size.

Anti-interrupted sampling repeater jamming based on intra-pulse frequency modulation slope agile radar waveform joint FrFT

Interrupted sampling repeater jamming (ISRJ) is coherent with the radar-transmitted signal, which can form multi-false targets at the radar receiver. Therefore, ISRJ suppression is a compelling task in electronic counter-countermeasure. Intra-pulse frequency coded signals are not well energy-concentrated in the time-frequency (TF) domain, resulting in interference and target overlapping in the TF domain when the number of intermittent samplings and the number of forwarding times is large. To solve this problem, an anti-ISRJ method is proposed based on intra-pulse frequency modulation (FM) slope agile radar waveform joint fractional Fourier transform (FrFT). Firstly, the radar transmits the intra-pulse FM slope agile signal, and the adjacent sub-pulses are modulated with positive and negative FM slopes. Next, the echo signals are divided into multiple slices with the same sub-pulse timing as the transmitted signals. Then, utilizing the characteristics of transceiver time-sharing and energy suppression of the ISRJ, the FrFT is performed on each slice of the echo, and the interfered echo slices can be identified by fractional search and fractional order comparison. Finally, the interference in interfered echo slices is suppressed by fractional filtering. Simulation results show that the proposed method can recognize the interfered echo slice 100 % when the jamming-to-noise ratio and jamming-to-signal ratio (JSR) are both greater than 0 dB and do not generate false alarms when the signal-to-noise ratio is greater than 0 dB and JSR is greater than 10 dB. Fractional filtering reduces the loss of target energy in the process of interference suppression. Simulation results also verify the effectiveness of the proposed method against three typical types of synchronous ISRJ and the compound interferences formed by the combination of different types of synchronous ISRJ.

Assessment of knee pain from MR imaging using a convolutional Siamese network.

It remains difficult to characterize the source of pain in knee joints either using radiographs or magnetic resonance imaging (MRI). We sought to determine if advanced machine learning methods such as deep neural networks could distinguish knees with pain from those without it and identify the structural features that are associated with knee pain. We constructed a convolutional Siamese network to associate MRI scans obtained on subjects from the Osteoarthritis Initiative (OAI) with frequent unilateral knee pain comparing the knee with frequent pain to the contralateral knee without pain. The Siamese network architecture enabled pairwise learning of information from two-dimensional (2D) sagittal intermediate-weighted turbo spin echo slices obtained from similar locations on both knees. Class activation mapping (CAM) was utilized to create saliency maps, which highlighted the regions most associated with knee pain. The MRI scans and the CAMs of each subject were reviewed by an expert radiologist to identify the presence of abnormalities within the model-predicted regions of high association. Using 10-fold cross-validation, our model achieved an area under curve (AUC) value of 0.808. When individuals whose knee WOMAC pain scores were not discordant were excluded, model performance increased to 0.853. The radiologist review revealed that about 86% of the cases that were predicted correctly had effusion-synovitis within the regions that were most associated with pain. This study demonstrates a proof of principle that deep learning can be applied to assess knee pain from MRI scans. • Our article is the first to leverage a deep learning framework to associate MR images of the knee with knee pain. • We developed a convolutional Siamese network that had the ability to fuse information from multiple two-dimensional (2D) MRI slices from the knee with pain and the contralateral knee of the same individual without pain to predict unilateral knee pain. • Our model achieved an area under curve (AUC) value of 0.808. When individuals who had WOMAC pain scores that were not discordant for knees (pain discordance < 3) were excluded, model performance increased to 0.853.

Magnetic Resonance Imaging of the Spine at the Douala General Hospital (Cameroon)

Objectives: The objective of this study was to evaluate the interest of MRI in the diagnosis of spinal disorders in our area. Method: It was a cross-sectional, descriptive and retrospective study during a nine-month period from January to September 2015 involving all patients who performed a spine MRI in the Imaging Department of Douala General Hospital. All the patients were scanned using an open-sided mid-field MRI APERTO LUCENT (0.4 T) using sagittal and axial slices in T1-weighted and T2-weighted FSE spin echo and STIR sagittal slices and T1 gado. Water-fat saturation (WFS) slices were obtained after injection of a contrast agent. All the data collected were analyzed using Microsoft Excel 2010 and Sphinx version 4.0. Results: 220 patients were recruited. The mean age was 46.34. There was male predominance with a sex ratio of 1.5. The main indication was lumbar spine pain (36.8%), followed by cervical spine pain, sensory and motor disorder. Neurosurgeon (33.6%), neurologist (23.1%) and rheumatologist (13.6%) were the main referring physicians. The lumbar spine was the most explored (53.2%). Discal hernia (46.6%), arthrosis (31.3%) and degenerative disc disease (25.5%) were the main observed lesion. Infectious disorders were mainly represented by spondylitis (5%); Traumatic disorders by spondylolisthesis (8.6%). Tumors were mainly metastasis (4%). 21.3% of MRI were normal. MRI-clinical concordance was 78.63%. Conclusion: MRI allows an accurate assessment of spinal and spinal cord pathologies without exposing patients to radiation. It helped to confirm or refute the diagnosis suspected by clinics. However, its availability is limited in our country.

MO‐G‐18C‐08: Increasing Throughput of a Clinical MR Protocol for Prostate Cancer with a Factor of Two Using Multiband Imaging

Purpose:To increase throughput of a clinical, multi‐parametric, prostate MRI protocol by individual scan acceleration using multiband excitation, in which multiple slices are excited simultaneously, and CAIPIRINHA.Methods:A healthy subject was scanned on a 3T clinical MR‐system with a 16‐channel torso receive array. A T2w‐TSE scan from a clinical prostate MR protocol was acquired to simulate three acceleration Methods: (1) traditional in‐plane parallel imaging (SENSE) (R=2), (2) multi‐slice parallel imaging (MS‐SENSE, R=2), in which two slices are acquired simultaneously and (3) multi‐slice CAIPIRINHA (R=2), in which one of the simultaneously acquired slices is shifted with FOV/2 with respect to the other slice. The normalized expected SNR was calculated within an ROI in the center of the slice. To demonstrate the feasibility of multiband MRI for the prostate, two 2D gradient echo slices (TE/TR=2.4ms/5.0ms, FA=20°, FOV=250×405mm2, voxelsize=0.5×0.5×4mm3, slice gap=20mm) were excited simultaneously using a numerically designed multiband RF pulse. The slices were acquired either with or without shifting the second slice by FOV/2 (i.e. CAIPIRINHA).Results:Simulations showed an expected relative SNR of 0.67 for in‐plane two‐fold SENSE acceleration, 0.14 for multi‐slice SENSE, and 0.94 for multi‐slice CAIPIRINHA within the ROI (SNR=1 for non‐accelerated acquisition). In‐vivo multiband experiments demonstrated that separation of the simultaneously acquired slices was practically impossible when slices folded on top of each other. However, the multi‐slice CAIPIRINHA experiment, showed low g‐factors and good image quality after unfolding.Conclusion:We demonstrated that the twofold multiband acceleration with CAIPIRINHA technique is the most SNR beneficial compared to the other acceleration techniques with only a moderate SNR penalty compared to the non‐accelerated acquisition. In‐vivo experiments demonstrated the feasibility of two‐fold CAIPIRINHA acceleration for pelvic MRI. This can be used to e.g. increase patient throughput, SNR or temporal resolution of the scans included in the multiparametric prostate MR protocol.

Application Accuracy of Automatic Registration in Frameless Stereotaxy

Objective: We compared the application accuracy of an infrared-based neuronavigation system when used with a novel automatic registration with its application accuracy when standard fiducial-based registration is performed. Methods: The automatic referencing tool is based on markers that are integrated in the headrest holder we routinely use in our intraoperative magnetic resonance imaging (MRI) setting and can be detected by the navigation software automatically. For navigation targeting we used a Plexiglas phantom with 32 notched rods of different heights. The phantom was fixed in the head holder and multiple optimized gradient echo slices containing the clamp-integrated markers were acquired. After that we measured a T₁ MPRAGE sequence with a slice thickness of 1.0 mm for navigation. The deepest points of the surface of the rods were defined as target points in image space. In three measurement series we referenced the phantom once with 4, once with 7 fiducials and twice automatically. In one series we performed only one automatic registration. The localization error was measured 3 times per rod and registration. Results: The median localization errors for standard registration with 7 fiducials were between 1.2 and 3.05 mm. With 4 fiducials, medians were in the range from 1.87 to 2.21 mm. For the automatic registration we obtained median localization errors between 0.88 and 2.13 mm. In 6 of the 8 samples that were compared the automatic registration showed an application accuracy that was highly significantly better (p < 0.001 in most cases) than that of fiducial-based standard registration. Conclusion: The application accuracy found for automatic referencing is at least not worse than that for standard registration no matter whether 4 or 7 fiducial markers were used. Therefore, its use in the operating room is feasible. In combination with intraoperative MRI it may become a favorable alternative to standard fiducial-based registration especially when an intraoperative update of navigation data is necessary.

Reliability of atlas-derived coordinates in deep brain stimulation

In deep brain stimulation the way to define and localize the optimal target for the individual patient is still under debate. The objective of our study was to investigate the reliability of atlas derived data by comparing them with direct targeting on MR images. We investigated 28 STN targets in 14 volunteers. The stereotactic coordinates of the dorso-lateral subthalamic nucleus (STN), were determined in 5 different ways for both STNs of each individual volunteer: 1. directly, on axial T2WI spin echo slices, 2. directly, on coronal T2WI spin echo slices and after fusion of data sets: 3. indirectly, on an axial atlas plate, 4. indirectly, on a coronal atlas plate, 5. indirectly, 12 mm lateral, 3 mm posterior and 3 mm inferior to mid-AC-PC. The differences between MRI derived targets on axial vs. coronal slices were not statistically significant. After detection of the atlas derived targets the resulting x-coordinates were found more lateral than after direct detection on both, axial and coronal T2-weighted images (p < 0.001). On axial images y-coordinates were located more anterior (p = 0.240) on atlas derived targets and more posterior when target localizations were compared on coronal slices (p < 0.001). z-Coordinates were more superior after atlas targeting compared to MRI targeting (p < 0.001). Differences up to 6.21 mm occurred. Despite the limitations concerning image distortions and slice thickness, direct target planning on MRI, regarding our results, is more reliable than targeting solely based on atlas derived data. Only MRI gives us detailed information about the individual configurations of central structures in every single patient. However, targets, which are not detectable on MRI like the nucleus ventralis intermedius have to be planned using stereotactic atlas information. In these cases intra-operative micro-electrode recording might help to better define the target region.

Imaging of the epilepsies

Imaging of epilepsy patients is challenging, since epileptogenic lesions (defined as structural lesions causally related to the epilepsy syndrome) may be small and often do not change during life. Prior clinical information about the epilepsy syndrome and the semiology of the seizures is needed in order to plan the examination properly. The effort to detect an epileptogenic lesion is directed to partial (focal) epilepsy syndromes whereas--by definition--no lesion is identified in idiopathic epilepsies. Most patients with partial epilepsies suffer from mesial temporal lobe epilepsies. In these patients, 2- to 3-mm-thick T2-weighted and fluid-attenuated inversion-recovery (FLAIR) fast spin echo slices along or perpendicular to the temporal lobe length axis have the highest diagnostic efficacy. In contrast, in patients with extratemporal lobe epilepsies perpendicular FLAIR slices through the anatomic region, from which, due to clinical and EEG criteria, the seizures are likely to originate, are preferred. The imaging features of common epileptogenic lesions (hippocampal sclerosis, long-term epilepsy-associated tumours, focal cortical dysplasias, vascular malformations, encephalitis including limbic and Rasmussen's encephalitis, gyral scarring including ulegyria) are detailed in the second section of this paper.