Approaching one nanosecond temporal resolution with square-wave-based control signals for interference gating.

Temporal resolution in time-resolved cone-beam CT (TR-CBCT) imaging is often limited by the time needed to acquire a complete dataset for image reconstruction. With the recent developments of performing nearly limited-view artifact-free reconstruction from data in a limited-view angle range and a prior image, temporal resolution of TR-CBCT imaging can be improved from the initial 0.2 frame per second (fps) to 1 fps which indicated a factor of five improvement in temporal resolution. In this paper, a new technique was introduced to further improve temporal resolution from 1.0 fps to about 7.5 fps which indicates a factor of more than 30 times improvement in temporal resolution for slow C-arm CBCT acquistions. This new technique was developed for multi-sweep data acquistion protocol and it is referred to as enhanced SMART-RECON (eSMART-RECON) in this paper. Numerical phantoms with ground truth and in vivo human subject data were used to validate the proposed eSMART-RECON method.

Purpose: To sample the breathing cycle and obtain accurate target volumes, 4DCT requires the entire field of view (FOV) to be illuminated during one breathing period. However, interplay effects between internal motion and couch pitch may adversely impact the temporal resolution, thereby blurring object edges. This work performs a characterization of exponential 4DCT reconstruction to highlight potential gains over standard cos2 weighted reconstruction algorithm. Methods: A respiratory motion platform translated several objects in the superior-inferior direction at varied breathing rates (8–20 breaths/minute) and couch pitches (0.06–0.1 A.U.) to evaluate the interplay between parameters. Ten-phase 4DCTs were acquired (0.5s rotation) and data were reconstructed with cos2 and exponential weighting factors. To isolate a metric to quantify temporal resolution (i.e. remove couch interplay effects), a small object was translated in the anterior-posterior direction. Full-width half maximum (FWHM) intensity distributions were quantified between reconstruction algorithms and a static case. 4DCT sinogram data for fifteen lung and abdomen patients were retrospectively reconstructed using cos2 and exponential weighting factors. Image subtractions were generated to elucidate intensity and boundary differences. Results: After taking the static object size into account, the FWHM of exponential weighting was 1.5±1.2 mm (range: 0.1–4.1) as compared to the FWHM of cos2 3.4±2.4 mm (range: 0.3–8.0). This translated to estimated improvements in temporal resolution of 33.5±48.2 ms (range: 0.03–170.9). Slower breathing periods, faster couch pitches, and intermediate 4DCT phases where velocity is highest showed a tendency to have the largest improvements in temporal resolution with exponential reconstruction. For patient cases, coronal views showed less blurring at object boundaries and local intensity differences near moving features. Conclusion: Exponential weighted 4DCT offers potential for improving temporal resolution in 4DCT, thus improving the image sharpness near the boundaries. Understanding the potential implications on delineation ability is an important next step of this work. The submitting institution holds research agreements with Philips Healthcare.

Lagrangian trajectories are frequently used to trace air parcels from the troposphere to the stratosphere through the tropical tropopause layer (TTL), and the coldest temperatures of these trajectories have been used to reconstruct water vapor variability in the lower stratosphere, where water vapor’s radiative impact on Earth’s surface is strongest. As such, the ability of these trajectories to accurately capture temperatures encountered by parcels in the TTL is crucial to water vapor reconstructions and calculations of water vapor’s radiative forcing. A potential source of error for trajectory calculations is the resolution of the input data. Here, we explore how improving the temporal and spatial resolution of model input data impacts the temperatures measured by Lagrangian trajectories that cross the TTL during boreal winter using ERA5 reanalysis data. We do so by comparing the temperature distribution of trajectories computed with data downsampled in either space or time to those computed with ERA5's maximum resolution. We find that improvements in temporal resolution from 6 hour to 3 or 1 hour lower the cold point temperature distribution, with the mean cold point temperature decreasing from 185.9 K to 185.0 K or 184.5 K for trajectories run during boreal winters of 2010 to 2019, while improvements to vertical resolution from that of MERRA2 data (the GEOS5 model grid) to full ERA5 resolution also lower the distribution but are of secondary importance, and improvements in horizontal resolution from 1° x 1° to 0.5° x 0.5° or 0.25° x 0.25° have negligible impacts. We suggest that this is caused by excess vertical dispersion near the tropopause when temporal resolution is degraded, which allows trajectories to cross the TTL without passing through the coldest regions, and by undersampling of the four--dimensional temperature field when either temporal or vertical resolution is reduced.

Lagrangian trajectories are frequently used to trace air parcels from the troposphere to the stratosphere through the tropical tropopause layer (TTL), and the coldest temperatures of these trajectories have been used to reconstruct water vapor variability in the lower stratosphere, where water vapor’s radiative impact on Earth’s surface is strongest. As such, the ability of these trajectories to accurately capture temperatures encountered by parcels in the TTL is crucial to water vapor reconstructions and calculations of water vapor’s radiative forcing. A potential source of error for trajectory calculations is the resolution of the input data. Here, we explore how improving the temporal and spatial resolution of model input data impacts the temperatures measured by Lagrangian trajectories that cross the TTL during boreal winter using ERA5 reanalysis data. We do so by comparing the temperature distribution of trajectories computed with data downsampled in either space or time to those computed with ERA5's maximum resolution. We find that improvements in temporal resolution from 6 hour to 3 or 1 hour lower the cold point temperature distribution, with the mean cold point temperature decreasing from 185.9 K to 185.0 K or 184.5 K for trajectories run during boreal winters of 2010 to 2019, while improvements to vertical resolution from that of MERRA2 data (the GEOS5 model grid) to full ERA5 resolution also lower the distribution but are of secondary importance, and improvements in horizontal resolution from 1° x 1° to 0.5° x 0.5° or 0.25° x 0.25° have negligible impacts. We suggest that this is caused by excess vertical dispersion near the tropopause when temporal resolution is degraded, which allows trajectories to cross the TTL without passing through the coldest regions, and by undersampling of the four--dimensional temperature field when either temporal or vertical resolution is reduced.

Lagrangian trajectories are frequently used to trace air parcels from the troposphere to the stratosphere through the tropical tropopause layer (TTL), and the coldest temperatures of these trajectories have been used to reconstruct water vapor variability in the lower stratosphere, where water vapor’s radiative impact on Earth’s surface is strongest. As such, the ability of these trajectories to accurately capture temperatures encountered by parcels in the TTL is crucial to water vapor reconstructions and calculations of water vapor’s radiative forcing. A potential source of error for trajectory calculations is the resolution of the input data. Here, we explore how improving the temporal and spatial resolution of model input data impacts the temperatures measured by Lagrangian trajectories that cross the TTL during boreal winter using ERA5 reanalysis data. We do so by comparing the temperature distribution of trajectories computed with data downsampled in either space or time to those computed with ERA5's maximum resolution. We find that improvements in temporal resolution from 6 hour to 3 or 1 hour lower the cold point temperature distribution, with the mean cold point temperature decreasing from 185.9 K to 185.0 K or 184.5 K for trajectories run during boreal winters of 2010 to 2019, while improvements to vertical resolution from that of MERRA2 data (the GEOS5 model grid) to full ERA5 resolution also lower the distribution but are of secondary importance, and improvements in horizontal resolution from 1° x 1° to 0.5° x 0.5° or 0.25° x 0.25° have negligible impacts. We suggest that this is caused by excess vertical dispersion near the tropopause when temporal resolution is degraded, which allows trajectories to cross the TTL without passing through the coldest regions, and by undersampling of the four--dimensional temperature field when either temporal or vertical resolution is reduced.

Lagrangian trajectories are frequently used to trace air parcels from the troposphere to the stratosphere through the tropical tropopause layer (TTL), and the coldest temperatures of these trajectories have been used to reconstruct water vapor variability in the lower stratosphere, where water vapor’s radiative impact on Earth’s surface is strongest. As such, the ability of these trajectories to accurately capture temperatures encountered by parcels in the TTL is crucial to water vapor reconstructions and calculations of water vapor’s radiative forcing. A potential source of error for trajectory calculations is the resolution of the input data. Here, we explore how improving the temporal and spatial resolution of model input data impacts the temperatures measured by Lagrangian trajectories that cross the TTL during boreal winter using ERA5 reanalysis data. We do so by comparing the temperature distribution of trajectories computed with data downsampled in either space or time to those computed with ERA5's maximum resolution. We find that improvements in temporal resolution from 6 hour to 3 or 1 hour lower the cold point temperature distribution, with the mean cold point temperature decreasing from 185.9 K to 185.0 K or 184.5 K for trajectories run during boreal winters of 2010 to 2019, while improvements to vertical resolution from that of MERRA2 data (the GEOS5 model grid) to full ERA5 resolution also lower the distribution but are of secondary importance, and improvements in horizontal resolution from 1° x 1° to 0.5° x 0.5° or 0.25° x 0.25° have negligible impacts. We suggest that this is caused by excess vertical dispersion near the tropopause when temporal resolution is degraded, which allows trajectories to cross the TTL without passing through the coldest regions, and by undersampling of the four--dimensional temperature field when either temporal or vertical resolution is reduced.

Abstract. Lagrangian trajectories are frequently used to trace air parcels from the troposphere to the stratosphere through the tropical tropopause layer (TTL), and the coldest temperatures of these trajectories have been used to reconstruct water vapor variability in the lower stratosphere, where water vapor's radiative impact on Earth's surface is strongest. As such, the ability of these trajectories to accurately capture temperatures encountered by parcels in the TTL is crucial to water vapor reconstructions and calculations of water vapor's radiative forcing. A potential source of error for trajectory calculations is the resolution of the input data. Here, we explore how improving the spatial and temporal resolution of model input data impacts the temperatures measured by Lagrangian trajectories that cross the TTL during boreal winter using ERA5 reanalysis data. We do so by comparing the temperature distribution of trajectories computed with data downsampled in either space or time to those computed with ERA5's maximum resolution. We find that improvements in temporal resolution from 6 to 3 and 1 h lower the cold point temperature distribution, with the mean cold point temperature decreasing from 185.9 to 185.0 and 184.5 K for reverse trajectories initialized at the end of February for each year from 2010 to 2019, while improvements to vertical resolution from that of MERRA2 data (the GEOS5 model grid) to full ERA5 resolution also lower the distribution but are of secondary importance, and improvements in horizontal resolution from 1∘ × 1∘ to 0.5∘ × 0.5∘ or 0.25∘ × 0.25∘ have negligible impacts to trajectory cold points. We suggest that this is caused by excess vertical dispersion near the tropopause when temporal resolution is degraded, which allows trajectories to cross the TTL without passing through the coldest regions, and by undersampling of the four-dimensional temperature field when either temporal or vertical resolution is reduced.

In a recently published paper by Li et al (2018 Phys. Med. Biol. 63 075001), reconstruction parameters were optimized for the so-called synchronized multiArtifact reduction with tomographic reconstruction (SMART-RECON) method to enable time-resolved Cone beam computed tomography angiography (TR-CBCTA) from a single short-scan CBCT data set. However, the paper did not quantitatively address how much temporal resolution can be improved by using the SMART-RECON algorithm in TR-CBCTA. The purpose of this note was to present a method to quantify this temporal resolution improvement factor and to use that method to quantify the improvement in temporal resolution using SMART-RECON and optimized reconstruction parameters. In the method proposed in this note, the potential temporal blurring caused by SMART-RECON was modeled as a convolution between a temporal Gaussian blurring kernel and the ground truth temporal enhancement curve. The width parameter of the resulting Gaussian blurring kernel was used as a surrogate metric for temporal resolution to quantify the achievable temporal resolution for the conventional filtered backprojection (FBP) and SMART-RECON methods. The ratio of the surrogate temporal resolutions for the two reconstruction methods was calculated to quantify the factor of temporal resolution improvement. The quantitative results show that the temporal resolution is improved by a factor of 4.5 using SMART-RECON compared with FBP.

To improve the temporal resolution in an optical delay system that uses a conventional mechanical delay stage, we integrate an in-line liquid crystal (LC) wave retarder. Previous implementations of LC optical delay methods are limited due to the small temporal window provided. Using a conventional mechanical delay stage system in series with the LC wave retarder, the temporal window is lengthened. Additionally, the limitation on temporal resolution resulting from the minimum optical path alteration (resolution of 400 nm) of the conventionally used mechanical delay stage is reduced via the in-line wave retarder (resolution of 50 nm). Interferometric autocorrelation measurements are conducted at multiple laser emission frequencies (349, 357, 375, 394, and 405 THz) using the in-line LC and conventional mechanical delay stage systems. The in-line LC system is compared to the conventional mechanical delay stage system to determine the improvements in temporal resolution relating to maximum resolvable frequency. This work demonstrates that the integration of the in-line LC system can extend the maximum resolvable frequency from 375 to 3000 THz. The in-line LC system is also applied for measurement of terahertz pulses.

Cardiac Computed Tomography Technology and Dose-reduction Strategies

Velocity imaging with phase contrast (PC) MRI is a noninvasive tool for quantitative blood flow measurement in vivo. A shortcoming of conventional PC imaging is the reduction in temporal resolution as compared to the corresponding magnitude imaging. For the measurement of velocity in a single direction, the temporal resolution is halved because one must acquire two differentially flow-encoded images for every PC image frame to subtract out non-velocity-related image phase information. In this study, a high temporal resolution PC technique which retains both the spatial resolution and breath-hold length of conventional magnitude imaging is presented. Improvement by a factor of 2 in the temporal resolution was achieved by acquiring the differentially flow-encoded images in separate breath-holds rather than interleaved within a single breath-hold. Additionally, a multiecho readout was incorporated into the PC experiment to acquire more views per unit time than is possible with the single gradient-echo technique. A total improvement in temporal resolution by approximately 5 times over conventional PC imaging was achieved. A complete set of images containing velocity data in all three directions was acquired in four breath-holds, with a temporal resolution of 11.2 ms and an in-plane spatial resolution of 2 mm x 2 mm.

Review of recent advances in analytical techniques for the determination of neurotransmitters

Phase-correlated CT, as it is used for cardiac imaging, is the most popular and the most important but also the most demanding special CT application in the clinical routine, today. Basically, it fulfills the four-dimensional imaging task of depicting a quasiperiodically moving object at any desired motion phase with significantly reduced motion artifacts. Although image quality with phase-correlated reconstruction is far better than with standard reconstruction, there are motion artifacts remaining and improvements of temporal resolution are required. As a well-known alternative to simply decreasing rotation time, we consider a spiral cone-beam CT scanner that has G x-ray guns and detectors mounted. We call this a multisource or a multithreaded CT scanner. Aiming for improved temporal resolution the relative temporal resolution tau, which measures the fraction of a motion period that enters the image, is studied as a function of the motion rate (heart rate) and the degree of scan overlap (pitch value) for various configurations. The parameters to optimize are the number of threads G and the interthread parameters delta alpha and delta z, which are the angular and the longitudinal separation between adjacent threads, respectively. To demonstrate the improvements approximate image reconstruction of multithreaded raw data is performed by using a generalization of the extended parallel back projection cone-beam reconstruction algorithm [Med. Phys. 31(6), 1623-1641 (2004)] to the case of multithreaded CT. Reconstructions of a simulated cardiac motion phantom and of simulated semi-antropomorphic phantoms are presented for two and three threads and compared to the single-threaded case to demonstrate the potential of multithreaded cardiac CT. Patient data were acquired using a clinical double-threaded CT scanner to validate the theoretical results. The optimum angle delta alpha between the tubes is 90 degrees for a double-threaded system, and for triple-threaded scanners it is 60 degrees or 120 degrees. In all cases, delta z = 0 results as an optimum, which means that the threads should be mounted in the same transversal plane. However, the dependency of the temporal resolution on delta z is very weak and a longitudinal separation delta z not = 0 would not deteriorate image quality. The mean temporal resolution achievable with an optimized multithreaded CT scanner is a factor of G better than the mean temporal resolution obtained with a single-threaded scanner. The standard reconstructions showed decreased cone-beam artifacts with multithreaded CT compared to the single-threaded case. Our phase-correlated reconstructions demonstrate that temporal resolution is significantly improved with multithreaded CT. The clinical patient data confirm our results.

Recent Technologic Advances in Multi-Detector Row Cardiac CT

Optimized auditory transcranial alternating current stimulation improves individual auditory temporal resolution