Purpose: To determine the impact of constrained reconstruction techniques on quantitative CT (qCT) of the lung parenchyma and airways for low x-ray radiation dose. Methods: Measurement of small airways with qCT remains a challenge, especially for low x-ray dose protocols. Images of the COPDGene quality assurance phantom (CTP698, The Phantom Laboratory, Salem, NY) were obtained using a GE discovery CT750 HD scanner for helical scans at x-ray radiation dose-equivalents ranging from 1 to 4.12 mSv (12-100 mA s current-time product). Other parameters were 40 mm collimation, 0.984 pitch, 0.5 s rotation, and 0.625 mm thickness. The phantom was sandwiched between 7.5 cm thick water attenuating phantoms for a total length of 20 cm to better simulate the scatter conditions of patient scans. Image data sets were reconstructed using STANDARD (STD), DETAIL, BONE, and EDGE algorithms for filtered back projection (FBP), 100% adaptive statistical iterative reconstruction (ASIR), and Veo reconstructions. Reduced (half) display field of view (DFOV) was used to increase sampling across airway phantom structures. Inner diameter (ID), wall area percent (WA%), and wall thickness (WT) measurements of eight airway mimicking tubes in the phantom, including a 2.5 mm ID (42.6 WA%, 0.4 mm WT), 3 mm ID (49.0 WA%, 0.6 mm WT), and 6 mm ID (49.0 WA%, 1.2 mm WT) were performed with Airway Inspector (Surgical Planning Laboratory, Brigham and Women's Hospital, Boston, MA) using the phase congruency edge detection method. The average of individual measures at five central slices of the phantom was taken to reduce measurement error. Results: WA% measures were greatly overestimated while IDs were underestimated for the smaller airways, especially for reconstructions at full DFOV (36 cm) using the STD kernel, due to poor sampling and spatial resolution (0.7 mm pixel size). Despite low radiation dose, the ID of the 6 mm ID airway was consistently measured accurately for all methods other than STD FBP. Veo reconstructions showed slight improvement over STD FBP reconstructions (4%-9% increase in accuracy). The most improved ID and WA% measures were for the smaller airways, especially for low dose scans reconstructed at half DFOV (18 cm) with the EDGE algorithm in combination with 100% ASIR to mitigate noise. Using the BONE + ASIR at half BONE technique, measures improved by a factor of 2 over STD FBP even at a quarter of the x-ray dose. Conclusions: The flexibility of ASIR in combination with higher frequency algorithms, such as BONE, provided the greatest accuracy for conventional and low x-ray dose relative to FBP. Veo provided more modest improvement in qCT measures, likely due to its compatibility only with the smoother STD kernel. C
Purpose To determine the effects of iterative reconstruction (IR) and high frequency kernels on quantitative computed tomography (qCT) density measures at reduced X-ray dose. Materials and Methods The COPDGene 2 Phantom (CTP 698, The Phantom Laboratory, Salem, NY) with four embedded lung mimicking foam densities (12lb, 20lb, and 4lb), as well as water, air, and acrylic reference inserts was imaged using a GE 64 slice CT750 HD scanner in helical mode with four current-time products ranging from 12–100 mAs. The raw acquired data was reconstructed using standard (STD – low frequency) and Bone (high frequency) kernels with filtered back projection (FBP), 100% ASIR, and Veo reconstruction algorithms. The reference density inserts were manually segmented using Slicer3D (www.slicer.org) and the mean, standard deviation, and histograms of the segmented regions were generated using Fiji (http://fiji.sc/Fiji) for each reconstruction. Measurements of threshold values placed on the cumulative frequency distribution of voxels determined by these measured histograms at 5%, PD5phant, and 15%, PD15phant, (analogous to the relative area below −950 HU (RA950) and percent density 15 (PD15) in human lung emphysema quantification, respectively), were also performed. Results The use of high-resolution kernels in conjunction with ASIR, and Veo did not significantly affect the mean Hounsfield units (HU) of each of the density standards (<4 HU deviation) and current-time products within the phantom when compared with the STD+FBP reconstruction conventionally used in clinical applications. A truncation of the scanner reported HU values at −1024 that shifts the mean towards more positive values was found to cause a systematic error in lower attenuating regions. Use of IR drove convergence toward the mean of measured histograms (~100–137% increase in the number measured voxels at the mean of the histogram) while the combination of Bone+ASIR preserved the standard deviation of HU values about the mean compared to STD+FBP, with the added effect of improved spatial resolution and accuracy in airway measures. PD5phant and PD15phant were most similar between the Bone+ASIR and STD+FBP in all regions except those affected by the −1024 truncation artifact. Conclusions Extension of the scanner reportable HU values below the present limit of −1024 will mitigate discrepancies found in qCT lung densitometry in low-density regions. The density histogram became more sharply peaked and standard deviation was reduced for IR, directly effecting density thresholds, PD5phant and PD15phant, placed on the cumulative frequency distribution of each region in the phantom, which serve as analogs to RA950 and PD15 typically used in lung density quantitation. The combination of high frequency kernels (Bone) with ASIR mitigates this effect and preserves density measures derived from the image histogram. Moreover, previous studies have shown improved accuracy of qCT airway measures of wall thickness (WT) and wall area percentage (WA%) when using high frequency ...
Objective We reduced the CT-reconstructed field of view (FOV), increasing pixel density across airway structures and reducing partial volume effects, to determine whether this would improve accuracy of airway wall thickness quantification. Methods We performed CT imaging on a lung phantom and 29 subjects. Images were reconstructed at 30, 15, and 10 cm FOV using a medium-smooth kernel. Cross-sectional airway dimensions were compared at each FOV with repeated-measures analysis of variance. Results Phantom measurements were more accurate when FOV decreased from 30 to 15 cm (p<0.05). Decreasing FOV further to 10 cm did not significantly improve accuracy. Human airway measurements similarly decreased by decreasing FOV (p<0.001). Percent changes in all measurements when reducing FOV from 30 to 15 cm were less than 3%. Conclusions Airway measurements at 30 cm FOV are near the limits of CT resolution using a medium-smooth kernel. Reducing reconstructed FOV would minimally increase sensitivity to detect differences in airway dimensions.
An English springer spaniel developed laryngeal paralysis immediately after a ventral slot decompression surgery to treat an intervertebral disc extrusion that was causing a C1–T2 myelopathy with cervical hyperaesthesia. Postsurgical stabilisation in the intensive care unit is described. This included mechanical ventilation, tracheostomy tube placement and care, and laryngeal tie-back surgery aftercare. Common complications after ventral slot decompression include pain, severe haemorrhage and deterioration in the neurological status. Laryngeal paralysis has not yet been reported in dogs after a ventral slot.
A 14‐year‐old Irish sport horse presented to our institution with a history of right forelimb lameness and left‐sided back pain. Radiography and nuclear scintigraphy were performed under sedation and the horse was diagnosed with overriding dorsal spinous processes, also known as kissing spine syndrome. Surgical treatment consisted of dorsal spinous process ostectomy and desmotomy under general anaesthesia. This case report summarises the perianaesthetic management, which included an erector spinae plane block as part of a multimodal analgesic approach.
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