Minutes Of Scan Time Research Articles

Efficient functional localization of language regions in the brain

Important recent advances in the cognitive neuroscience of language have been made using functional localizers to demarcate language-selective regions in individual brains. Although single-subject localizers offer insights that are unavailable in classic group analyses, they require additional scan time that imposes costs on investigators and participants. In particular, the unique practical challenges of scanning children and other special populations has led to less adoption of localizers for neuroimaging research with these theoretically and clinically important groups. Here, we examined how measurements of the spatial extent and functional response profiles of language regions are affected by the duration of an auditory language localizer. We compared how parametrically smaller amounts of data collected from one scanning session affected (i) consistency of group-level whole-brain parcellations, (ii) functional selectivity of subject-level activation in individually defined functional regions of interest (fROIs), (iii) sensitivity and specificity of subject-level whole-brain and fROI activation, and (iv) test-retest reliability of subject-level whole-brain and fROI activation. For many of these metrics, the localizer duration could be reduced by 50-75% while preserving the stability and reliability of both the spatial extent and functional response profiles of language areas. These results indicate that, for most measures relevant to cognitive neuroimaging studies, the brain's language network can be localized just as effectively with 3.5 min of scan time as it can with 12 min. Minimizing the time required to reliably localize the brain's language network allows more effective localizer use in situations where each minute of scan time is particularly precious.

Multiresolution radial MRI to reduce IDLE time in pre-beam imaging on an MR-Linac (MR-RIDDLE)

Online adaptive MR-guided radiation therapy improves treatment quality at the expense of considerable longer treatment time. The treatment lengthening partially originates from the preparatory (pre-beam) MR imaging required to encode all the information needed for contour propagation, contour adaptation and replanning. MRI requires several minutes of scan time before the encoded information is converted to usable images, which results in long idle times before the first clinical tasks are performed. In this study we propose a novel imaging sequence, called MR-RIDDLE, that reduces the idle time and therefore speeds-up the workflow in online MR-guided radiation therapy. MR-RIDDLE enables multiresolution image reconstruction to commence during data acquisition where low resolution images are available within one minute, after which the data collection continuous for subsequent high-resolution image updates. We demonstrate that the low resolution images can be used to accurately propagate contours from the pre-treatment scan. For abdominothoracic tumours MR-RIDDLE inherently captures a motion-blurred representation of the mid-position, which we were able to deblur using a combination of an internal motion surrogate and auto-adaptive soft-gating filters. Our results demonstrate that MR-RIDDLE provides a robust, flexible and time-efficient strategy for pre-beam imaging, even for cases with large respiratory movements or baseline shifts within the acquisition. We anticipate that this novel concept of parallelising the MR imaging and the clinical tasks has the potential to considerably speed-up and streamline the online MR-guided radiation therapy workflow.

Design and Validation of Synchronous QCT Calibration Phantom: Practical Methodology

IntroductionQuantitative computed tomography (QCT) can supplement dual x-ray absorptiometry by enabling geometric and compartmental bone assessments. Whole-body spiral CT scanners are widely available and require a short scanning time of seconds, in contrast to peripheral QCT scanners, which require several minutes of scanning time. This study designed and evaluated the accuracy and precision of a homemade QCT calibration phantom using a whole-body spiral CT scanner. Materials and MethodsThe QCT calibration phantom consisted of K2HPO4 solutions as reference. The reference material with various concentrations of 0, 50, 100, 200, 400, 1000, and 1200 mg/cc of K2HPO4 in water were used. For designing the phantom, we used the ABAQUS software. ResultsThe phantoms were used for performance assessment of QCT method through measurement of accuracy and precision errors, which were generally less than 5.1% for different concentrations. The correlation between CT numbers and concentration were close to one (R2 = 0.99). DiscussionBecause whole-body spiral CT scanners allow central bone densitometry, evaluating the accuracy and precision for the easy to use calibration phantom may improve the QCT bone densitometry test. ConclusionThis study provides practical directions for applying a homemade calibration phantom for bone mineral density quantification in QCT technique.

A simple way to higher speed atomic force microscopy by retrofitting with a novel high-speed flexure-guided scanner

A typical line-scan rate for a commercial atomic force microscope (AFM) is about 1 Hz. At such a rate, more than four minutes of scanning time is required to obtain an image of 256 × 256 pixels. Despite control electronics of most commercial AFMs permit faster scan rates, default piezoelectric X–Y scanners limit the overall speed of the system. This is a direct consequence of manufacturers choosing a large scan range over the maximum operating speed for a X–Y scanner. Although some AFM manufacturers offer reduced-scan area scanners as an option, the speed improvement is not significant because such scanners do not have large enough reduction in the scan range and are mainly targeted to reducing the overall cost of the AFM systems. In this article, we present a simple parallel-kinematic substitute scanner for a commercial atomic force microscope to afford a higher scanning speed with no other hardware or software upgrade to the original system. Although the scan area reduction is unavoidable, our modified commercial XE-70 AFM from Park Systems has achieved a line scan rate of over 50 Hz, more than 10 times faster than the original, unmodified system. Our flexure-guided X–Y scanner can be a simple drop-in replacement option for enhancing the speed of various aging atomic force microscopes.

Subtle blood-brain barrier leakage rate and spatial extent: Considerations for dynamic contrast-enhanced MRI.

Dynamic contrast-enhanced (DCE) MRI can be used to measure blood-brain barrier (BBB) leakage. In neurodegenerative disorders such as small vessel disease and dementia, the leakage can be very subtle and the corresponding signal can be rather noisy. For these reasons, an optimized DCE-MRI measurement and study design is required. To this end, a new measure indicative of the spatial extent of leakage is introduced and the effects of scan time and sample size are explored. Dual-time resolution DCE-MRI was performed in 16 patients with early Alzheimer's disease (AD) and 17 healthy controls. The leakage rate (Ki ) and volume fraction of detectable leaking tissue (vL ) to quantify the spatial extent of BBB leakage were calculated in cortical gray matter and white matter using noise-corrected histogram analysis of leakage maps. Computer simulations utilizing realistic Ki histograms, mimicking the strong effect of noise and variation in Ki values, were performed to understand the influence of scan time on the estimated leakage. The mean Ki was very low (order of 10-4 min-1 ) and highly influenced by noise, causing the Ki to be increasingly overestimated at shorter scan times. In the white matter, the Ki was not different between patients with early AD and controls, but was higher in the cortex for patients, reaching significance after 14.5 min of scan time. To detect group differences, vL proved more suitable, showing significantly higher values for patients compared with controls in the cortex after 8 minutes of scan time, and in white matter after 15.5 min. Several ways to improve the sensitivity of a DCE-MRI experiment to subtle BBB leakage were presented. We have provided vL as an attractive and potentially more time-efficient alternative to detect group differences in subtle and widespread blood-brain barrier leakage compared with leakage rate Ki . Recommendations on group size and scan time are made based on statistical power calculations to aid future research.

TU‐A‐BRA‐01: A Robotic Multi‐Pinhole SPECT System for Onboard and Other Region‐Of‐Interest Imaging

Purpose: Radiation therapy beam guidance and modulation at treatment time could be substantially supported by onboard molecular and functional imaging capability. Currently there is very little range of technology available for this. Herein we propose and investigate a robotic multi‐pinhole SPECT system for this purpose. Methods: A 49‐pinhole system is designed with 7 pods and 7 pinholes per pod. Pod geometry is such that the full target region‐of‐interest (ROI) is within the FOV of all 7 pinholes for all pod distances exceeding a minimum distance from the ROI. Motion of the pods relative to one another can involve just 1 or 2 degrees of freedom per pod. Motion of the entire, composite 49‐pinhole system is provided by a robot. This design enables all 49 pinholes to view the full ROI throughout detector trajectories that can achieve sampling objectives, e.g. on line integrals measured, while also providing good resolution and sensitivity via close proximity to the ROI. The design is evaluated through computer simulation studies in which 7 and 10 mm diameter structures of 6‐to‐1 radiotracer uptake are added to the XCAT phantom. Results are compared to imaging with a compact parallel‐hole collimated detector, which is utilized as a reference for conventional SPECT imaging configurations. Results: For the 7 cm‐diameter target region of interest, the 49‐pinhole system shows markedly improved imaging as compared to the reference, parallel‐hole collimated detector. Most 7 mm and 10 mm diameter structures are readily visualized with 4 minute scans. Conclusions: In only a few minutes of scan time, the designed multi‐pinhole SPECT system can provide molecular and functional information about the target region as patients are in position for radiation therapy. This work is supported by NIH grant R21‐CA156390‐01A1.

Vessel encoded arterial spin labeling with cerebral perfusion: preliminary study

Objective To evaluate a noninvasive vessel encoded imaging for selective mapping of the flow territories of the left and right internal carotid arteries and vertebral-basilar arteries. Methods Seven volunteers [(33.5±4.1) years ; 3 men, 4 women] and 6 patients [(55.2 ± 3.2) years; 2 men,4women] were given written informed consent approved by the institutional review board before participating in the study. A pseudo-continuous tagging pulse train is modified to encode all vessels of interest. The selectivity of this method was demonstrated. Regional perfusion imaging was developed on the same arterial spin labeling sequence. Perfusion-weighted images of the selectively labeled cerebral arteries were obtained by subtraction of the labeled from control images. The CBF values of hemisphere, white matter, and gray matter of volunteers were calculated. The vessel territories on patients were compared with DSA. The low perfusion areas were compared with high signal areas on T2-FLAIR. Results High SNR maps of left carotid, right carotid, and basilar territories were generated in 8 minutes of scan time. Cerebral blood flow 100 g-1 were in agreement with data in the literature. Vessel encoded imaging in patients had a good agreement with DSA. The low perfusion areas were larger than high signal areas on T2-FLAIR. Conclusion We present a new method capable of evaluating both quantitatively and qualitatively the individual brain-feeding arteries in vivo. Key words: Magnetic resonance imaging; Perfusion; Cerebral arteries

SU-EE-A3-06: Onboard SPECT: Functional-Image-Based Target Localization

Purpose: To investigate clinical feasibility for functional‐image‐based target localization via onboard single photon emission computed tomography (onboard SPECT). Specifically, to understand lesion visibility and signal‐to‐noise ratio (SNR) of onboard SPECTimaging with the following simulated variables: lesion size, target‐to‐background radiotracer uptake, and scan time. Method and Materials: We simulated onboard SPECTimaging for a patient in treatment position who had received a diagnostic‐level dose of hypoxia radiotracer. The planning CT of a typical breast cancer patient with lung mets was segmented into bone, lung, and soft tissue. Lesions were simulated in the right lung that varied in diameter (0.5cm, 1cm, 1.5cm, 2cm, 3cm) and radiotracer uptake (lesion:lung:soft tissue — 6:1:3, 12:1:3, 18:1:3). Radiotracer concentration was 1.4μCi/g in aerobic soft tissue. Attenuation was modeled for 140 keV photons. Projection images were simulated for a gamma camera with parallel collimation, and Poisson noise was added to projections to simulate several scan times: 1min, 2min, 5min, 10min, 20min. Noisy projection images were reconstructed by OSEM (10 subsets, 5 iterations). Post‐filtered reconstructed images were then analyzed by plotting image profiles across each lesion and calculating SNR.Results: One minute scan time provided good visualization of a 2cm lesion with 12:1:3 uptake ratio. When scan time remained constant at 5 minutes, 2cm lesions were visible for each uptake ratio. In another simulation, a 1cm lesion (18:1:3) was clearly visible following 5 minutes of scan time. As expected, SNR generally improved with increased lesion size, scan time, and relative radiotracer uptake. Conclusion: Scan times on the order of a few minutes yield sufficient information to visualize lesions as small as 1cm in the lung. These results suggest that onboard SPECT may be effective for real‐time and functional‐image‐based target localization.

Le « de Sèze » magnétique

The authors propose that a coronal STIR sequence with large FOV, similar to the de Sèze projection, including lumbar spine, sacrum, pelvis and hips should be obtained in all patients as part of the lumbar spine MRI protocol. For an additional few minutes of scanning time, this additional sequence could demonstrate the presence of lesions (hips, pelvis, sacrum, SI joints, retroperitoneum…) that would otherwise go undetected on standard sagittal and axial MRI images of the lumbar spine.

Technique for rapid in vitro single-cell elastography

Statistically meaningful assays require scanning a large number of cells in a short time. Here we present a technique for rapid in vitro single-cell elastography. The technique is based on atomic force acoustic microscopy but (1) requires only a few minutes of scan time, (2) can be used on live cells briefly removed from most of the nutrient fluid, (3) does negligible harm or damage to the cell, (4) provides semiquantitative information on the distribution of modulus across the cell and (5) yields data with 1- to 10-nm resolution. We describe the new technique in detail, apply it to baby hamster kidney cells, verify the results and calibrate the images with atomic force microscope force-distance measurements. The technique enables rapid assessment of physical/biochemical signals on the cell modulus and contributes to current understanding of cell mechanics.

Improving the Efficiency of Gynecologic Sonography With 3-Dimensional Volumes

The purpose of this study was to determine whether 3-dimensional (3D) sonography can provide a rapid, efficient, and accurate way to do a transvaginal gynecologic scan compared with traditional 2-dimensional (2D) sonography. Thirty-five consecutive patients who underwent gynecologic sonography formed the study cohort. After a standard 2D transvaginal scan was done, including measurements of the endometrium and abnormalities, 4 volume acquisitions were obtained, encompassing the uterus (2 volumes) and the ovaries. These volumes were reviewed offline without any patient information. Endometrium and other measurements were performed on the volumes. The 2D and 3D results were compared by paired t tests. The mean time needed for the standard 2D scan was 2.6 minutes compared with 1.07 minutes for the 3D volume acquisitions. The mean time for the reconstruction, measurement, and interpretation of the volumes offline was 1.19 minutes. The mean time for the entire 3D examination (both parts) was 2.26 minutes (P = .047, comparing 2D with total 3D). There was no significant difference between the measurements of the endometrium, fibroids, and ovarian cysts when comparing 2D and reconstructed 3D images. Two-dimensional and 3D sonography differed little in their ability to identify the organs and the abnormalities on the scans. This study shows that a complete transvaginal gynecologic examination can be done in 1.07 minutes of scan time and interpreted offline in an additional 1.19 minutes. The 35 cases were scanned and interpreted with the use of 3D sonography in 79.17 minutes total compared with 91.46 minutes of 2D scan time (P = .047). The accuracy of the scan was similar for both techniques.

OC4.03: Just images: The shadows of the IUD

Objective: To determine whether 3D ultrasound can provide a rapid and efficient way to do a transvaginal GYN scan compared to the traditional 2D ultrasound. Methods: 35 consecutive patients presenting for GYN sonography formed the study cohort. After doing standard 2D transvaginal scan including measurements of the endometrium and abnormalities, 3–4 volume acquisitions were obtained, encompassing the uterus (1–2 volumes) and the ovaries. These volumes were reviewed off line without any patient information. The endometrium and other measurements were performed on the volumes. The 2D and 3D results were compared. Results: The mean time needed for the standard 2-D scan was 2.61 minutes compared with 1.07 minutes for the 3-D volume acquisitions. The mean time for the reconstruction, measurement and interpretation of the volumes off-line was 1.19 minutes. The mean time for the entire 3D exam (both parts) was 2.26 minutes (p = 0.047 comparing 2D to total 3D). The mean measurement of the endometrium was 6.69 mm and 6.64 mm using 2D and 3D respectively (p = 0.8). The mean measurements of the 27 ovarian cysts were 2.24 cm and 2.21 cm using 2D and 3D respectively (p = 0.7). The mean measurements of 9 fibroids were 4.3 cm and 3.98 cm using 2D and 3D respectively (p = 0.08). Discrepancies between the interpretation of the 2D and 3D exams: one ovary was seen better on 3D, one ovary was seen better on 2D. One endometrium was only measurable on 3D and one polyp seen only on 2D. Patients with dermoids, endometriomas, cysts, fibroids etc. were detected equally well using both methods. Conclusion: This study shows that a complete transvaginal GYN exam can be done in 1.07 minutes of scan time and interpreted off line in an additional 1.19 minutes. The 35 cases were scanned and interpreted using 3D in 79.14 minutes total compared to 91.46 minutes of 2D scan time. The accuracy of the scan was similar using both techniques. Adoption of this approach brings ultrasound into the era of volume imaging.