Identifying Lymph Nodes and Their Statuses from Pretreatment Computer Tomography Images of Patients with Head and Neck Cancer Using a Clinical-Data-Driven Deep Learning Algorithm.

BACKGROUND: Head and neck cancer is highly prevalent in Taiwan. Its treatment mainly relies on clinical staging, usually diagnosed from images. A major part of the diagnosis is whether lymph nodes are involved in the tumor. We present an algorithm for analyzing clinical images that integrates a deep learning model with image processing and attempt to analyze the features it uses to classify lymph nodes. METHODS: We retrospectively collected pretreatment computed tomography images and surgery pathological reports for 271 patients diagnosed with, and subsequently treated for, naïve oral cavity, oropharynx, hypopharynx, and larynx cancer between 2008 and 2018. We chose a 3D UNet model trained for semantic segmentation, which was evaluated for inference in a test dataset of 29 patients. RESULTS: We annotated 2527 lymph nodes. The detection rate of all lymph nodes was 80%, and Dice score was 0.71. The model has a better detection rate at larger lymph nodes. For those identified lymph nodes, we found a trend where the shorter the short axis, the more negative the lymph nodes. This is consistent with clinical observations. CONCLUSIONS: The model showed a convincible lymph node detection on clinical images. We will evaluate and further improve the model in collaboration with clinical physicians.

A specific absorption rate reduction method for simultaneous multislice magnetic resonance imaging.

This study proposes a modified Shinnar-Le Roux method to synthesize the excitation radio frequency (RF) pulse for a 2D gradient echo (GRE) based simultaneous multi-slice (SMS) magnetic resonance imaging (MRI) with features of low specific absorption rate (SAR) and small out-of-slice ripple. This synthesis method for SMS RF pulses employs thinner slice bandwidth and lower multislice offset frequencies to reduce SAR values and adopts a weighted Parks-McClellan algorithm to reduce sidelobes. Formulas for estimating relative SAR values of the SMS pulses are also introduced. Relative SAR values and out-of-slice ripples of the proposed and typical RF pulses with different parameters are presented. In simultaneous 5-slice phantom and 3-slice human brain imaging, SMS pulses synthesized with the proposed method achieve 32% and 28% SAR values of standard pulses while providing similar image qualities. Typical RF pulses such as sinc x cos can also take advantage of the proposed method and offer lower SAR values for SMS imaging. The RF pulse synthesized using the proposed method features low SAR, small sidelobes, and consistent image quality for 2D GRE-based SMS MRI. This method is applicable to the synthesis of typical SMS RF pulses for significant SAR reduction.

Single-frequency excitation wideband MRI (SE-WMRI).

PURPOSE: In this study, single-frequency excitation wideband magnetic resonance imaging (MRI) (SE-WMRI) was proposed to obtain high-quality accelerated images by reducing phase-encoding steps while applying separation gradients. METHODS: A zig-zag k-space trajectory with reduced phase-encoding steps and an increased readout sampling rate was proposed. A unique gradient design with buffer intervals near the trajectory turns was employed to avoid undersampling and image artifacts. A gridding method and Fourier transform were used for image reconstruction. Quantitative analysis was performed on phantom images to investigate the characteristics of the acceleration method. RESULTS: The proposed method showed evident improvements in the accelerated phantom images, substantially reducing the ringing and blurring artifacts found using previous methods. Furthermore, the accelerated images exhibited the same signal-to-noise ratio as standard imaging. The accelerated in vivo experiment also produced the same quality as standard imaging. CONCLUSIONS: The proposed SE-WMRI method can effectively remove image artifacts and acquire images of higher temporal or spatial resolutions with less compromise.

Multiple-frequency excitation wideband MRI (ME-WMRI).

PURPOSE: In this study multiple-frequency excitation wideband MRI (ME-WMRI), a technique designed to acquire simultaneously excited images without blurring was proposed. METHODS: ME-WMRI consists of (a) a coherent acquisition sequence that applies refocusing gradient during readout to mitigate signal dephasing, and (b) a signal enhancement procedure that further reduces image blurring. This two-step method was tested on phantom imaging andin vivo imaging with up to 3.84 pixel blur. RESULTS: Imaging results in both phantom andin vivo show that the lost details were successfully restored in the blur-mitigated images, and the accelerated images were comparable to standard images. CONCLUSIONS: The proposed ME-WMRI method can effectively undo the image blurring, and thus removes the limitation on fast simultaneous multislice MRI systems with a large acceleration factor.

Development of NTU standard Chinese Brain Template: morphologic and functional comparison with MNI template using magnetic resonance imaging.

BACKGROUND AND PURPOSE: The brain structure mismatch between western and eastern people may lead to an inappropriate interpretation of neurocognitive studies. To minimize this interracial misinterpretation, we developed the National Taiwan University Chinese Brain Template (NTU-CBT). METHODS: 102 (M/F = 55/47) healthy Chinese subjects were recruited and received 3T MR brain scans. The template development processes were based on the construction process of Montreal Neurological Institute (MNI) template. Further pilot functional magnetic resonance imaging (fMRI) studies with blocked design visual stimulation and foot tapping task were performed on 3 volunteers and applied to both MNI template and NTU-CBT for analyses. RESULTS: 7 subjects were excluded due to motion artifacts. The average brain size of 95 (M/F = 50/45) subjects was 16.0 cm in length, 13.9 cm in width and 11.3 cm in height, which was 88.9%, 97.9% and 84.3% of the size of MNI template, respectively. Maximum dimensional differences came from the height of superior brain and the length of posterior brain. The average activation voxel volume of the fMRI studies applying to NTU-CBT was 80.7% of that to MNI template in visual stimulation, and 72.8% in foot tapping task. Noticeable mismatches were noted between interpolating original data to NTU-CBT and MNI template. CONCLUSIONS: Morphologic differences between MNI template and NTU-CBT do lead to spatial mismatch in functional studies, especially at cortical regions of superior and posterior brain. With the development of NTU-CBT, we look forward to more accurate interpretation in neurocognitive studies for Chinese subjects.

Localized high-resolution MR imaging of rat brain architecture using micro-fabricated receive-only RF coil.

This study introduced a localized approach for magnetic resonance microscopy (MRM) of the rat brain. A single-loop radiofrequency (RF) receiver coil designed for micro-imaging was developed by using electromagnetic simulation software widely used in communication fields. With transmit-only and receive-only (TORO) configuration, receive-only surface coil can achieve higher signal-to-noise ratio (SNR) at localized brain region. Corpus callosum and hippocampus were landmarks to evaluate the capacity of the proposed coil. On a 3T MRI system, high-resolution MRI of the dissected rat brain was acquired with spatial resolution of 117x117x500 microm3. The achieved high local SNR and spatial resolution will provide valuable information for resolving the architecture of the rat brain.

Ultra-fast brain MR imaging using simultaneous multi-slice acquisition (SMA) technique.

Whole-brain images were acquired with a 2X acceleration factor by using Simultaneous Multi-slice Acquisition (SMA). Utilizing a Sinc pulse modulated by cosine/sine functions combined with an extra gradient along the slice-selection direction during acquisition, we are able to take multiple magnetic resonance images of different slice simultaneously. 2-slice and 4-slice SMA experiments were also conducted to demonstrate the feasibility of this method; also a volumetric image of the phantom was taken, achieving an overall 3X acceleration.

Preliminary study of planar RF coils for Magnetic Resonance Microscopy.

In this study, we attempt to do a preliminary study of planar RF coils that are aimed for the application of Magnetic Resonance Microscopy (MRM). We will discuss the requirements and considerations for designing such a device. And at last, we conducted a small experiment to show that the design solution we propose is in the correct direction.