Mm In Magnitude Research Articles

Reproducibility of Deep-Inspiration Breath Hold treatments on Halcyon™ performed using the first clinical version of AlignRT InBore™: Results of CYBORE study

Background and purposeTo investigate the reproducibility of deep-inspiration breath hold (DIBH) breast cancer treatments on Halcyon™ performed using the first clinical version of AlignRT InBore™ (Vision RT Ltd., London, UK), a Halcyon’s SGRT dedicated solution. Materials and methodsThe ease and feasibility of DIBH treatments was retrospectively investigated for the initial 22 left breast cancer patients treated on Halcyon™ using AlignRT InBore™. Setup time, Cone beam computed tomography (CBCT) imaging and analysis time as well as overall treatment time were recorded. Online and offline review of CBCT images was undertaken to verify the compliance of breast, heart, spine, sternum and diaphragmatic domes positions. ResultsMean duration of patient setup, CBCT analysis and overall treatment time were 4 min, 1.1 min and 14 min respectively. Online review of 520 CBCT acquisitions by therapists showed minimal positioning shifts with AlignRT InBore™ guidance with mean value of vertical, longitudinal, and lateral shifts of 1.7 mm, −1.7 mm, and −0.2 mm respectively. Meanwhile, offline review of 115 CBCTs by the radiation oncologist, showed reproducible breath hold (BH) with average deviation of breast, heart, spine, sternum and diaphragmatic domes respectively within 2.4 mm, 2.9 mm, 3.3 mm, 3.2 mm and 4.5 mm in magnitude. ConclusionAlignRT InBore™ allows for accurate and reproducible DIBH on Halcyon™ with breast and heart organs’ positions within 3 mm in magnitude of expected position and fully compliant with planning margins (5 mm anisotropic CTV-PTV margins).

Extremely Sensitive Anomaly Detection in Pipe Networks Using a Higher-Order Paired-Impulse Response Function with a Correlator

Detection of anomalies in pipe networks (leaks, blockages, and wall deterioration) is critical for targeted pipe section replacement and maintenance in water distribution systems. A hydraulic signal-processing approach, termed the paired-impulse response function (paired-IRF), has been previously proposed for anomaly detection by transforming the persistent principal wave reflections by anomalies into distinctive paired spikes. In this paper, a new higher-order paired-IRF has been derived, which considers both principal and higher-order wave reflections by the anomalies. A correlator has then been designed (and incorporated into the higher-order paired-IRF) to highlight anomaly-induced spikes and suppress noise. A looped pipe network with realistic background noise was assembled in the laboratory to examine the efficacy of the new methods. According to the experimental results, it is observed that (1) the higher-order paired-IRF is an extremely sensitive detection technique and clearly identifies anomalies inducing wave reflections as small as 0.5% of the injected wave magnitude; (2) its sensitivity is sufficiently accurate when using micropressure waves as small as 20 mm in magnitude and contaminated by 2-m background pressure fluctuations; and (3) the proposed advanced correlator highlights the anomaly-induced spikes in the paired-IRF trace in a noisy environment.

Limitations in One‐Dimensional (an)Elastic Earth Models for Explaining GPS‐Observed M2 Ocean Tide Loading Displacements in New Zealand

AbstractGPS observations of ocean tide loading displacements can help infer the regional anelastic properties of the asthenosphere. We estimate M2 ocean tide loading displacements at 170 GPS sites in New Zealand and compare these to modeled values using a range of numerical tide and radially symmetric (1D) elastic and anelastic Earth models. Regardless of the model combination, we are unable to reduce the strong spatial coherence of the M2 residuals across the North Island where they reach 0.4 mm (2%). The best fit in the North Island is obtained when combining the FES2014b tide model with spatially variable ocean density and water compressibility, and the STW105 Earth model. The residuals exhibit a change of ∼0.3 mm in magnitude between the Taupo Volcanic Zone and the east coast (∼100 km), suggesting that this region's laterally varying, shallow rheological structure may need to be considered to explain these observations.

Effect of Teaching Session on Resident Ability to Identify Anatomic Landmarks and Anterior Cruciate Ligament Footprint: A Study Using 3-Dimensional Modeling.

Background:Femoral tunnel positioning in anterior cruciate ligament reconstruction (ACLR) is an intricate procedure that requires highly specific surgical skills.Purpose:To report the ability of residents to identify femoral landmarks and the native ACL footprint before and after a structured formal teaching session as a reflection of overall surgical skill training for orthopaedic surgery residents in Canada.Study Design:Controlled laboratory study.Methods:A total of 13 senior orthopaedic residents were asked to identify a femoral landmark and an ACL footprint on ten 3-dimensional (3D)–printed knee models before and after a teaching session during the fall of 2018. The 3D models were made based on actual patients with different anatomic morphologic features. ImageJ software was used to quantify the measurements, which were then analyzed through use of descriptive statistics.Results:Before and after the teaching session, residents attempted to identify a specific anatomic location (bifurcate and intercondylar ridge intersection) with a mean error per participant ranging from 5.00 to 10.95 mm and 4.79 to 12.13 mm in magnitude, respectively. Furthermore, before and after the teaching session, residents identified the specific position to perform the surgical procedure (ACL femoral footprint), with a mean error per participant ranging from 4.58 to 8.80 mm and 3.87 to 11.07 mm in magnitude, respectively. The teaching session resulted in no significant improvement in identification of either the intersection of the bifurcate and intercondylar ridges (P = .9343 in the proximal-distal axis and P = .8133 in the anteroposterior axis) or the center of the femoral footprint (P = .7761 in the proximal-distal axis and P = .9742 in the anteroposterior axis).Conclusion:Although a formal teaching session was combined with a hands-on session that entailed real surgical instrumentation and fresh cadaveric specimens, the intervention seemed to have no direct impact on senior residents’ performance or their ability to demonstrate the material taught. This puts into question the format and efficacy of present teaching methods. Also, it is possible that the 3D spatial perception required to perform these skills is not something that can be taught effectively through a teaching session or at all. Further investigation is required regarding the effectiveness and application of surgical skill laboratories and simulations on the competencies of orthopaedic residents.

Detection of land subsidence and its relationship with land cover types using ESA Sentinel satellite data: a case study of Quetta Valley, Pakistan

ABSTRACTThis paper presents the analysis of land subsidence as a result of excessive groundwater abstraction for irrigation and domestic supply in Quetta valley, Pakistan. The European Space Agency (ESA) Sentinel–1 and Sentinel–2 satellite data is used to identify and categorize the spatial distribution of land subsidence. The aquifer geology and observed groundwater table are used to establish the relationship between land subsidence and groundwater abstraction. For this, we performed Persistent Scattering Interferometry (PSIn) analysis using the Sentinel–1 Synthetic Aperture Radar (SAR) imagery to develop 28 maps of land subsidence covering a period of 16 October 2014 to 22 November 2016. The interferometry results matched well with the land subsidence values measured at the Global Positioning System (GPS) ground station with a mean absolute error of 5.7 mm and coefficient of determination of 0.94. The land subsidence values at each pixel of the map were classified according to the land cover types of the study area. Here, the map of land cover types was developed using the multispectral image of Sentinel–2A satellite. The results revealed that, during the 2–year period, the entire study area has suffered from varying degree of accumulated land subsidence ranging between 10 and 280 mm in magnitude, which was linearly proportional to the depth and drawdown of groundwater table observed at four piezometers located in the study area. The magnitude of land subsidence across the study area showed a strong correlation with land covers. The urban area and orchard vegetation with a large amount of groundwater abstraction showed an excessive amount of cumulative land subsidence, while the seasonally cultivated and barren land are slightly affected by land subsidence.

Air-kerma strength determination of an HDR 192 Ir source including a geometric sensitivity study of the seven-distance method.

To perform an in-air air-kerma strength (SK) calibration of the Bebig model Ir2.A85-2 192Ir high-dose rate (HDR) brachytherapy source manufactured by Mallinckrodt Medical (Westerduinweg, Germany) with the NIST-traceable seven-distance technique established by the University of Wisconsin. A comparison was made between the reference air-kerma rate (RAKR) reported on a certificate from the Physikalisch-Technische Bundesanstalt (Berlin, Germany) (PTB) primary laboratory and the SK determined at the University of Wisconsin Madison Radiation Research Center (UWMRRC). A theoretical sensitivity study was performed to investigate the impact that variations in the experimental setup have on the computed SK from the seven-distance algorithm in order to determine if the uncertainty budget for the seven-distance method should be expanded. The manufacturer-reported SK for the source was compared to the SK determined from the University of Wisconsin Accredited Dosimetry Calibration Laboratory (UWADCL) transfer standard well chambers and the seven-distance technique. Monte Carlo techniques (MCNP6) were employed to compare the theoretical SK calibration coefficients of a Standard Imaging (Middleton, WI) HDR1000 Plus well chamber using Standard Imaging model 70010 and model 70110 source holders to determine if a holder dependence was present. Radiochromic film (EBT3, Ashland) exposures were performed to assess the dose distribution of the source in phantom. The seven-distance algorithm was coded in MATLAB®(R2013b) and benchmarked with MCNP6 with the capacity to model distance offset behaviors among nominal positions. This offset model was used in a Monte Carlo simulation coded in MATLAB to determine the average uncertainty in the SK calculations from the seven-distance algorithm. The measured SK using the seven-distance technique at the UWMRRC agreed with the RAKR reported on the PTB source certificate and the SK on the Mallinckrodt source certificate to within 0.28% and -0.79%, respectively. It was found that the difference between the SK measured from the transfer standard well chambers at the UWADCL and the seven-distance method was between 0.13% and 0.30% at the 95% confidence level. Monte Carlo results showed negligible differences between the simulated SK calibration coefficient for an HDR1000 Plus well chamber using the model 70010 or model 70110 source holder. The autoradiographs from the source in Virtual WaterTM showed that the dose distribution is symmetric. Additionally, the sensitivity study performed in MATLAB showed that the SK calculated with the seven-distance algorithm could deviate by 0.24% from randomly generated distance offsets within 1mm in magnitude. The differences between the SK measurements determined from the seven-distance technique and the accredited UWADCL measurement results were within the k=2 uncertainty reported for an accredited calibration. Excellent agreement was found between the measured SK and RAKR methods used at the UWMRRC and PTB, respectively. Additionally, the sensitivity study has shown that the seven-distance algorithm accurately determines the SK of a source while having a variable chamber offset among nominal positions; the uncertainty budget for the seven-distance method does not need to be expanded at this time. It has been determined that the current standard used by the UWADCL for well chamber calibrations is valid for the Bebig model Ir2.A85-2 192Ir brachytherapy source.

Mathematical model and geometrical model of double pitch ZN-type worm gear set based on generation mechanism

The current researches on the tooth surface mathematical equations and the theory of gearing mainly pay attention to the ordinary type worm gear set (e.g., ZN, ZA, or ZK). The research of forming mechanism and three-dimensional modeling method for the double pitch worm gear set is not enough. So there are some difficulties in mathematical model deducing and geometry modeling of double pitch ZN-type worm gear set based on generation mechanism. In order to establish the mathematical model and the precise geometric model of double pitch ZN-type worm gear set, the structural characteristics and generation mechanism of the double pitch ZN-type worm gear set are investigated. Mathematical model of the ZN-type worm gear set is derived based on its generation mechanism and the theory of gearing. According to the mathematical model of the worm gear set which has been developed, a geometry modeling method of the double pitch ZN-type worm and worm gear is presented. Furthermore, a geometrical precision calculate method is proposed to evaluate the geometrical quality of the double pitch worm gear set. As a result, the maximum error is less than 6´10–4 mm in magnitude, thus the model of the double pitch ZN-type worm gear set is available to meet the requirements of finite element analysis and engineering application. The derived mathematical model and the proposed geometrical modeling method are helpful to guiding the design, manufacture and contact analysis of the worm gear set.

Vertical movements of the Murono mud volcano in Japan caused by the Naganoken Kamishiro Fault Earthquake in 2014

We observed vertical movements of the Murono mud volcano, Niigata, Japan, caused by the Naganoken Kamishiro Fault Earthquake (M = 6.7) on 22 November 2014. Precise levelling around the mud volcano was carried out on 27 November 2014, and the obtained elevation was compared with the data obtained for 11 November 2014. It was found that an elliptical uplift area, about 46 mm in magnitude and an order of magnitude smaller than that of the ones formed due to the past movements caused by the earthquakes in the same area, had been formed. It was considered that the structures of the shallow subsurface as well as the distance between the mud volcano and epicentre might play an important role in understanding the magnitude of vertical movements and distribution patterns.

Storage dynamics in hydropedological units control hillslope connectivity, runoff generation, and the evolution of catchment transit time distributions.

We examined the storage dynamics and isotopic composition of soil water over 12 months in three hydropedological units in order to understand runoff generation in a montane catchment. The units form classic catena sequences from freely draining podzols on steep upper hillslopes through peaty gleys in shallower lower slopes to deeper peats in the riparian zone. The peaty gleys and peats remained saturated throughout the year, while the podzols showed distinct wetting and drying cycles. In this region, most precipitation events are <10 mm in magnitude, and storm runoff is mainly generated from the peats and peaty gleys, with runoff coefficients (RCs) typically <10%. In larger events the podzolic soils become strongly connected to the saturated areas, and RCs can exceed 40%. Isotopic variations in precipitation are significantly damped in the organic-rich soil surface horizons due to mixing with larger volumes of stored water. This damping is accentuated in the deeper soil profile and groundwater. Consequently, the isotopic composition of stream water is also damped, but the dynamics strongly reflect those of the near-surface waters in the riparian peats. “pre-event” water typically accounts for >80% of flow, even in large events, reflecting the displacement of water from the riparian soils that has been stored in the catchment for >2 years. These riparian areas are the key zone where different source waters mix. Our study is novel in showing that they act as “isostats,” not only regulating the isotopic composition of stream water, but also integrating the transit time distribution for the catchment.Key PointsHillslope connectivity is controlled by small storage changes in soil unitsDifferent catchment source waters mix in large riparian wetland storageIsotopes show riparian wetlands set the catchment transit time distribution

TU‐C‐141‐01: The Development of a Set of Deformable Thermoplastic Materials That Mimic Tissue for Kilovoltage and Megavoltage Computed Tomography

Purpose: To construct a phantom designed to test deformable image registration algorithms, by developing a set of deformable thermoplastic materials that mimic tissue for both kilovoltage and megavoltage computed tomography. Methods: A material formulation was developed to represent muscle, water, and adipose using two polyurethanes capable of deforming in boiling water to produce anatomical deformations. The CT Hounsfield Units (HU) were tuned by doping the polyurethanes with a primary additive to increase the HU and a secondary additive to decrease it. To mimic actual bone, a plastic mixture whose HU was controlled by a tertiary additive was formulated to remain rigid in boiling water. A phantom prototype representing a central sagittal head and neck slice was constructed using the optimized materials. To ensure the phantom was anthropomorphic, its geometry was designed by contouring the major anatomical sites of a patient. The phantom was constructed so it could be opened along the sagittal midsection where a grid of 300 nonradioopaque markers were placed with 5mm spacing. The grid served as a nonradioopaque means of characterizing the 3D magnitude of a deformation with an optical camera. Results: The phantom materials were successfully tuned to be both kV and MV compatible and made to represent different tissues. The phantom constructed from these materials exhibited a similar HU contrast to an actual patient and was successfully deformed around the neck section, producing a clinically realistic deformation of several mm in magnitude. Conclusion: Using the formulated set of materials, an anthropomorphic phantom depicting different tissue types was built and deformed in 3D in a clinically realistic fashion. By measuring the positional changes of the optical markers, the constructed phantom can be used to physically verify deformable image registration algorithms. The work was supported in part by a UC Proof of Concept Program Commercialization Gap Grant.

TH‐C‐141‐09: A Comparison of MRI Distortion Between Scanners and Sequences for Radiotherapy Purposes

Purpose: To quantify the magnitude and distribution of system related geometric distortion present in MR images and determine the clinical radiotherapy sites for which this distortion is likely to have most impact. Methods: A commercially developed phantom conforming to AAPM standards for testing uniformity and linearity was imaged on 4 different MRI scanners. Similar T1 and T2 weighted clinical protocols were assessed. Each sequence and scanner had varying protocol parameters. Additionally, the direct impact of altering the receiver bandwidth (7.69 – 76.8kHz) on distortion and signal to noise was conducted on a standard spin echo sequence. The position of each phantom grid point was determined using in‐house MATLAB code, then compared to the known position as verified by a CT scan of the phantom to obtain the deformation matrix. Positions of anatomical sites (breast, lung, cervix, prostate and H&amp;N) were determined by analysing radiotherapy contoured data for 10 patients per site to establish the range of distortions occurring within these regions. Results: Distortions were observed to range from 0mm – 8.9mm in magnitude. Maximum distortion values measured across one of the similar clinical spin echo sequences tested varied from 2.75mm – 8.94mm. Similarly, comparison of a gradient echo sequence showed maximum distortions varied from 2.56mm – 3.33mm. Increasing the bandwidth reduced the maximum distortion present in the image by 3.49mm, at the cost of SNR. While distortion magnitudes and distributions varied, in most sequences the distortions began exceeding 2mm beyond a radial distance of 100mm from isocentre, where the oral cavity, lungs and breast lie. For regions where the prostate, cervix and brain stem lie, distortions were below 2mm. Conclusion: This work displays the variations in distortions present in MR images for different sequences and scanners. Distortions are of greatest magnitude in areas where the lung and breast would be located for radiotherapy purposes.

An Optimized System for Interventional Magnetic Resonance Imaging-Guided Stereotactic Surgery

Deep brain stimulation electrode placement with interventional magnetic resonance imaging (MRI) has previously been reported using a commercially available skull-mounted aiming device (Medtronic Nexframe MR) and native MRI scanner software. This first-generation method has technical limitations that are inherent to the hardware and software used. A novel system (SurgiVision ClearPoint) consisting of an aiming device (SMARTFrame) and software has been developed specifically for interventional MRI, including deep brain stimulation. To report a series of phantom and cadaver tests performed to determine the capability, preliminary accuracy, and workflow of the system. Eighteen experiments using a water phantom were used to determine the predictive accuracy of the software. Sixteen experiments using a gelatin-filled skull phantom were used to determine targeting accuracy of the aiming device. Six procedures in 3 cadaver heads were performed to compare the workflow and accuracy of ClearPoint with Nexframe MR. Software prediction experiments showed an average error of 0.9 ± 0.5 mm in magnitude in pitch and roll (mean pitch error, -0.2 ± 0.7 mm; mean roll error, 0.2 ± 0.7 mm) and an average error of 0.7 ± 0.3 mm in X-Y translation with a slight anterior (0.5 ± 0.3 mm) and lateral (0.4 ± 0.3 mm) bias. Targeting accuracy experiments showed an average radial error of 0.5 ± 0.3 mm. Cadaver experiments showed a radial error of 0.2 ± 0.1 mm with the ClearPoint system (average procedure time, 88 ± 14 minutes) vs 0.6 ± 0.2 mm with the Nexframe MR (average procedure time, 92 ± 12 minutes). This novel system provides the submillimetric accuracy required for stereotactic interventions, including deep brain stimulation placement. It also overcomes technical limitations inherent in the first-generation interventional MRI system.

Variability of Lung Tumor Measurements on Repeat Computed Tomography Scans Taken Within 15 Minutes

We use changes in tumor measurements to assess response and progression, both in routine care and as the primary objective of clinical trials. However, the variability of computed tomography (CT) -based tumor measurement has not been comprehensively evaluated. In this study, we assess the variability of lung tumor measurement using repeat CT scans performed within 15 minutes of each other and discuss the implications of this variability in a clinical context. Patients with non-small-cell lung cancer and a target lung lesion ≥ 1 cm consented to undergo two CT scans within a period of minutes. Three experienced radiologists measured the diameter of the target lesion on the two scans in a side-by-side fashion, and differences were compared. Fifty-seven percent of changes exceeded 1 mm in magnitude, and 33% of changes exceeded 2 mm. Median increase and decrease in tumor measurements were +4.3% and -4.2%, respectively, and ranged from 23% shrinkage to 31% growth. Measurement changes were within ± 10% for 84% of measurements, whereas 3% met criteria for progression according to Response Evaluation Criteria in Solid Tumors (RECIST; ≥ 20% increase). Smaller lesions had greater variability of percent measurement change (P = .005). Apparent changes in tumor diameter exceeding 1 to 2 mm are common on immediate reimaging. Increases and decreases less than 10% can be a result of the inherent variability of reimaging. Caution should be exercised in interpreting the significance of small changes in lesion size in the care of individual patients and in the interpretation of clinical trial results.

Evaluation of Targeting Errors in Ultrasound-Assisted Radiotherapy

A method for validating the start-to-end accuracy of a 3-D ultrasound (US)-based patient positioning system for radiotherapy is described. A radiosensitive polymer gel is used to record the actual dose delivered to a rigid phantom after being positioned using 3-D US guidance. Comparison of the delivered dose with the treatment plan allows accuracy of the entire radiotherapy treatment process, from simulation to 3-D US guidance, and finally delivery of radiation, to be evaluated. The 3-D US patient positioning system has a number of features for achieving high accuracy and reducing operator dependence. These include using tracked 3-D US scans of the target anatomy acquired using a dedicated 3-D ultrasound probe during both the simulation and treatment sessions, automatic 3-D US-to-US registration and use of infrared LED (IRED) markers of the optical position-sensing system for registering simulation computed tomography to US data. The mean target localization accuracy of this system was 2.5 mm for four target locations inside the phantom, compared with 1.6 mm obtained using the conventional patient positioning method of laser alignment. Because the phantom is rigid, this represents the best possible set-up accuracy of the system. Thus, these results suggest that 3-D US-based target localization is practically feasible and potentially capable of increasing the accuracy of patient positioning for radiotherapy in sites where day-to-day organ shifts are greater than 1 mm in magnitude. (E-mail: mikew@ece.ubc.ca)

How does nose blowing effect the computed tomography of paranasal sinuses in chronic sinusitis?

Objective: Our aim was to determine whether inward or outward movement of the secretions in the paranasal sinuses due to nose blowing after nasal decongestion has any effect on the paranasal sinus computed tomography (CT) images in patients with sinusitis and to asses whether nose blowing may result in misdiagnosis or overdiagnosis in radiological evaluation of sinusitis. Materials and methods: Twenty-four patients with chronic sinusitis were evaluated in an academic tertiary care hospital and data were collected prospectively. After coronal sinus computed tomography scans were performed at 100 mA setting which was half the value of the standard radiation dose suggested by the manufacturer, topical decongestion was applied to each nostril followed by nose blowing 10 min later. Sinus CT scans were then repeated at the same setting. We evaluated the mucosal thickness of medial, lateral, superior and inferior maxillary and frontal sinus walls and the maximal thickness in anterior ethmoidal cells. The measurements prior to and following nose blowing were compared with Wilcoxon signed ranks test. The obtained images were also staged using Lund–McKay staging system separately and the scores were compared with Student’s t-test. Results: We observed a tendency towards reduction in mucosal thickness after nose blowing. There were statistically significant differences between maxillary sinus inferior wall and frontal sinus inferior wall mucosal thickness values prior to and after nose blowing. The difference however was very small, about 0.5 mm in magnitude and Lund–McKay score did not change in any of the patients after nose blowing. Conclusion: Nose blowing and topical nasal decongestion does not have any effect on the diagnostic accuracy of sinus CT in chronic sinusitis patients.

CT image-guided intensity-modulated therapy for paraspinal tumors using stereotactic immobilization

Purpose: To design and implement a noninvasive stereotactic immobilization technique with daily CT image-guided positioning to treat patients with paraspinal lesions accurately and to quantify the systematic and random patient setup errors occurring with this method. Methods and Materials: A stereotactic body frame (SBF) was developed for “rigid” immobilization of paraspinal patients. The inherent accuracy of this system for stereotactic CT-guided treatment was evaluated with phantom studies. Seven patients with thoracic and lumbar spine lesions were immobilized with the SBF and positioned for 33 treatment fractions using daily CT scans. For all 7 patients, the daily setup errors, as assessed from the daily CT scans, were corrected at each treatment fraction. A retrospective analysis was also performed to assess what the impact on patient treatment would have been without the CT-based corrections (i.e., if patient setup had been performed only with the SBF). Results: The average magnitude of systematic and random errors from uncorrected patient setups using the SBF was approximately 2 mm and 1.5 mm (1 SD), respectively. For fixed phantom targets, the system accuracy for the SBF localization and treatment was shown to be within 1 mm (1 SD) in any direction. Dose-volume histograms incorporating these uncertainties for an intensity-modulated radiotherapy plan for lumbar spine lesions were generated, and the effects on the dose-volume histograms were studied. Conclusion: We demonstrated a very accurate and precise method of patient immobilization and treatment delivery based on a noninvasive SBF and daily image guidance for paraspinal lesions. The SBF provides excellent immobilization for paraspinal targets, with setup accuracy better than 2 mm (1 SD). However, for highly conformal paraspinal treatments, uncorrected systematic and random errors of 2 mm in magnitude can result in a significantly greater (>100%) dose to the spinal cord than planned, even though the planned target coverage may not change substantially. With daily CT guidance using the SBF, we showed that the maximal spinal cord dose is ensured to be within 10–15% of the planned value.

The Effect of Controlled Dynamization on Regenerate Bone Healing in Callotasis

We investigated whether controlled dynamization enhanced regenerate bone healing in callotasis of the tibia in 12 adult mongrel dogs. An average of 2 cm (≒ 10%) lengthening was obtained. The left hindlimb was allowed dynamization of 1 mm, 2 mm, and 3 mm in magnitude when 1 cm (≒ 5%) of lengthening was achieved, whereas the right hindlimb was not dynamized and served as a control. Bone mineral density (BMD) of the regenerate bone was measured periodically until nine weeks after the end of distraction. After sacrifice, uniaxial compression testing was performed. Relative BMD ratio and mechanical properties of the regenerate bone were significantly higher in the dynamization group than in the nondynamization group; no significant difference was found among dynamization subgroups, however. We conclude that 1 mm to 3 mm of elastic dynamization accelerates regenerate bone healing in callotasis of the canine tibia.

THE EFFECT OF CONTROLLED DYNAMIZATION ON REGENERATE BONE HEALING IN CALLOTASIS

We investigated whether controlled dynamization enhanced regenerate bone healing in callotasis of the tibia in 12 adult mongrel dogs. An average of 2 cm (≒ 10%) lengthening was obtained. The left hindlimb was allowed dynamization of 1 mm, 2 mm, and 3 mm in magnitude when 1 cm (≒ 5%) of lengthening was achieved, whereas the right hindlimb was not dynamized and served as a control. Bone mineral density (BMD) of the regenerate bone was measured periodically until nine weeks after the end of distraction. After sacrifice, uniaxial compression testing was performed. Relative BMD ratio and mechanical properties of the regenerate bone were significantly higher in the dynamization group than in the nondynamization group; no significant difference was found among dynamization subgroups, however. We conclude that 1 mm to 3 mm of elastic dynamization accelerates regenerate bone healing in callotasis of the canine tibia.

Transverse bending waves and the breaking broomstick demonstration

When a broomstick is supported at both ends by two wine glasses, a strong downward blow to the center will break the stick, leaving the wine glasses undisturbed, provided care is taken to cushion the wine glasses against an initial and brief downward motion of the ends of the broomstick. This downward motion is analyzed and estimated to be about 1 mm in magnitude. Qualitative experimental evidence of this motion is easily obtained using a force probe to monitor a light and nondestructive tap to a 2-m measuring stick. The method of analysis developed here leads to a simple derivation of the dispersion relation for transverse bending waves on a long rod.

Treatment strategies for daily life silent myocardial ischemia: A correlation with potential pathogenic mechanisms

Recent investigations of SMI occurring during daily life have advanced our understanding of the pathophysiology of myocardial ischemia. These contributions have directed our attention away from "chest pain" alone and physical exertion as the central provoking factor toward transient myocardial ischemia and its broader triggers and consequences. Transient myocardial ischemic episodes, the majority of which are silent, are found in a subset of patients with any clinical manifestations of CAD (eg, stable angina, unstable angina, myocardial infarction, and sudden death), as well as in those patients with CAD who are and have been totally asymptomatic. These episodes are an independent predictor of increased risk for future cardiac events. Most medical therapy and revascularization therapies have the potential to prevent or relieve these silent episodes; however, we do not yet know which method is superior in reducing SMI episodes or preventing future cardiac events. Furthermore, the benefit of reducing SMI versus the cost and potential morbidity of these chosen therapies is not known. At least three trials are now underway to examine some of these concerns (Table 2). Focus on pain relief alone does not appear to be an adequate approach to alter outcome in patients with CAD and may prove insufficient to control SMI. Until these issues are resolved, we believe a conservative approach to the management of patients with CAD is warranted. Documentation of ischemia (painful or painless) is essential. Three general principles should be kept in mind. First, the presence of detectable ischemia is of central importance. This information should be used in the overall risk assessment of the patient. Second, the level of concern or aggressiveness of treatment should be based on the risk associated with the ischemic abnormalities documented (Table 3). The exercise stress test is the most useful to begin this process. The detection of ischemic-type ST-segment depression, either silent or painful, at a low workload (eg, less than or equal to 120 beats per minute or less than or equal to 6.5 metabolic equivalents [METS]) implies high risk for adverse outcome. Likewise, these ST-segment changes occurring in leads that reflect multiple coronary artery distribution, of greater than 2 mm in magnitude and persisting for greater than 6 minutes, are all markers for high risk. Thallium redistribution defects occurring at low work loads, in multiple areas, associated with increased lung uptake and enlargement of the cardiac pool all imply high risk.(ABSTRACT TRUNCATED AT 400 WORDS)