Mathematical theory of stereotactic coordinate transformation: elimination of rotational targeting error by addition of a third reference point

2000 ◽  
Vol 92 (5) ◽  
pp. 884-888 ◽  
Author(s):  
Ethan Taub
Keyword(s):  
Coordinate Transformation ◽  
Reference Point ◽  
Magnetic Resonance Images ◽  
Reference Points ◽  
New Method ◽  
Midsagittal Plane ◽  
Content Type ◽  
Stereotactic Frame ◽  
Stereotactic Atlas ◽  
Source Of Error

✓ All frame-based stereotactic procedures require localization of an anatomical target within the coordinate system of the stereotactic frame. If the target is defined by its coordinates given in a stereotactic atlas (indirect localization), the neurosurgeon faces the mathematical task of transforming atlas coordinates into frame coordinates. In the method usually used, the frame coordinates of two reference points (the anterior and posterior commissures) are obtained from computerized tomography or magnetic resonance images, and serve as the basis for the coordinate transformation. This two-point algorithm relies on the additional assumption that the frame sits on the patient's head without exhibiting roll, that is, rotation about the anteroposterior axis (y axis). Usually this assumption is nearly, but not exactly, correct. An amount of roll as small as 3° can cause a targeting error on the order of 1 mm when a two-point algorithm is used. This potential source of error can be eliminated by using a new method of coordinate transformation, the derivation of which is mathematically reported in this article. The new method requires a third reference point located in the midsagittal plane, in addition to the two commissural reference points.

Aspirations or survival: decision modeling and the effect of focus of attention in risky choice

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Guy Moshe Ross
Keyword(s):  
Risk Taking ◽  
Reference Point ◽  
Effect Study ◽  
Focus Of Attention ◽  
Risky Choice ◽  
Reference Points ◽  
Aspiration Level ◽  
Content Type ◽  
Randomized Controlled Studies ◽  
Risky Option

Purpose This research aims to test focus of attention effects in risky choice. Design/methodology/approach As opposed to traditional aspiration-level theory, the shifting-focus concept introduces a second reference point, the survival point, and assumes a shifting focus of attention between the two reference points. In this conceptualization, risk-taking is a function of focus of attention on the survival reference point or the aspiration-level and resources relative to the two reference points. Four randomized controlled studies tested this concept. Findings Study 1 showed that with aspiration focus the probability of choosing a risky option was higher below an aspiration-level than above it. With survival focus, the effect was reversed. Study 2 found that close to the survival reference point, the probability of choosing a risky option was higher with aspiration focus relative to survival focus. Study 3 revealed that with scarce resources the risk taken was higher with aspiration focus than with survival focus, and the scarcer the resources the stronger was the effect. Study 4 demonstrated that with aspiration focus the risk taken was higher below an aspiration-level than above it. With survival focus the effect was reversed. Originality/value In addition to providing support for the validity of the shifting focus concept, this paper elaborates on the theoretical model by providing evidence for moderation effects. Risk-taking was affected by a focus of attention on one of two reference points, and the effect was moderated by resources relative to the two focal points. An advanced model is proposed to capture the effects of focus of attention and resources on risk-taking behavior.

Distortion in magnetic resonance images obtained for stereotactic localization

2000 ◽  
Vol 93 (supplement_3) ◽  
pp. 191-192 ◽  
Author(s):  
Lee Walton ◽  
Anna Hampshire ◽  
Paul Vaughan ◽  
David M. C. Forster ◽  
Andras A. Kemeny ◽  
...  
Keyword(s):  
Magnetic Resonance ◽  
Mr Imaging ◽  
Three Dimensional ◽  
Magnetic Resonance Images ◽  
Side Plate ◽  
Content Type ◽  
Potential Source ◽  
Minimal Distortion ◽  
Source Of Error ◽  
Fine Print

✓ The purpose of this paper was to note a potential source of error in magnetic resonance (MR) imaging. Magnetic resonance images were acquired for stereotactic planning for GKS of a vestibular schwannoma in a female patient. The images were acquired using three-dimensional sequence, which has been shown to produce minimal distortion effects. The images were transferred to the planning workstation, but the coronal images were rejected. By examination of the raw data and reconstruction of sagittal images through the localizer side plate, it was clearly seen that the image of the square localizer system was grossly distorted. The patient was returned to the MR imager for further studies and a metal clasp on her brassiere was identified as the cause of the distortion.

Reference points and method of payment in mergers

2018 ◽  
Vol 44 (2) ◽  
pp. 278-290
Author(s):  
Inga Chira ◽  
Jeff Madura
Keyword(s):  
Behavioral Finance ◽  
Reference Point ◽  
Reference Points ◽  
Content Type ◽  
Optimal Mix ◽  
Prefer Stock ◽  
Method Of Payment ◽  
The Impact ◽  
To Receive ◽  
Practical Implications

Purpose The purpose of this paper is to examine the impact of the target and bidder reference points on the method of payment in mergers. When considering initial and final results for target and bidder, the target appears to have more negotiating power than the bidder in achieving the financial mix preference that was initially articulated. Design/methodology/approach The authors examine the impact of target and bidder reference points on the consideration sought by the target and the consideration offered by the bidder. The authors test whether the target reference points has an impact on the final method of payment agreed upon by the target and the bidder. Findings The authors find that targets with a longer distance to their respective target reference points prefer to receive cash financing in the consideration sought, while bidders with a longer distance to their respective reference points prefer stock financing in consideration offered. The authors also find evidence that target’s longer distance to its reference point is associated with the use of cash over stock, while the bidder reference point has no impact on the final method of payment used in the merger. Practical implications These insights may be used by the management to formulate the optimal mix of financing in M&A transactions. Originality/value This is an original paper exploring the effect of behavioral finance on corporate decision making.

A Method to Center Extraction of Reference Point Algorithm in Reverse Engineering

2010 ◽  
Vol 142 ◽  
pp. 214-218
Author(s):  
Xiang Qian Che ◽  
Jun Ting Cheng ◽  
Sheng Bing Xiao ◽  
Jia Jun Ma
Keyword(s):  
Reverse Engineering ◽  
Computational Efficiency ◽  
Reference Point ◽  
Base Point ◽  
Recognition Algorithm ◽  
Reference Points ◽  
New Method ◽  
Sequential Algorithm ◽  
Object Surface ◽  
Point Data

In reverse engineering, in order to get the entire point data of the object surface, which must be merged from point data cloud obtained from different angles. And in order to acquire exactly merge effect, a method to stick reference points on object surface to acquire base point. Thus, the precision of center extraction of reference point affect the merge result. Firstly a new method to center extraction of reference point is presented based on the characteristics to the images in reverse engineering in this paper. And the new method is that the region recognition algorithm combining to least squares algorithm. Secondly, in order to improve the computational efficiency, the modified sequential algorithm is applied to optimize the region recognition. Lastly, the availability and accuracy to the new method are proved by the experiment.

Coordinate transformation uncertainty analysis and reduction using hybrid reference system for aircraft assembly

2018 ◽  
Vol 38 (4) ◽  
pp. 487-496 ◽  
Author(s):  
Zhengping Deng ◽  
Shuanggao Li ◽  
Xiang Huang
Keyword(s):  
Analytical Solution ◽  
Coordinate Transformation ◽  
Reference System ◽  
Solution Process ◽  
Simulation Method ◽  
Reference Points ◽  
Transformation Model ◽  
Content Type ◽  
Aircraft Assembly ◽  
Propagation Law

Purpose In aircraft assembly, standard reference points with nominal coordinates are commonly applied for coordinate transformation between multiple measurement stations and the assembly coordinate system. For several reasons in practical application, these points often fail to envelop the key assembly space, which leads to large transformation uncertainty. This paper aims to analyze and further reduce the coordinate transformation uncertainty by introducing a new hybrid reference system (HRS). Design/methodology/approach Several temporary extension points without known coordinates are added to enhance the tightness between different stations, especially at the weakness area in the network, thus constituting an HRS together with the existing standard reference points. The coordinate transformation model of the HRS-based measurement network is established based on an extend Gauss–Markov model. By using the geometrical differential property and variance-covariance propagation law, the covariance matrixes in the transformation model are calculated, and the analytical solution of the uncertainties of transformation parameters are ultimately derived. The transformation uncertainty of each check points is presented by Helmert error expression. Findings The proposed analytical solution of transformation uncertainty is verified using the state-of-the-art Monte Carlo simulation method, but the solution process is simpler and the computation expenses are much less. Practical implications The HRS with three temporary extension points is practically applied to a tail boom in-site measurement for assembly. The average transformation uncertainty has been reduced by 26 per cent to less than 0.05 mm. Originality/value The hybrid coordinate transformation model is proposed for the first time. The HRS method for transformation uncertainty reduction is more economical and practical than increasing the number of standard reference points.

A multi-block finite difference method for seismic wave equation in auxiliary coordinate system with irregular fluid–solid interface

2018 ◽  
Vol 35 (1) ◽  
pp. 334-362 ◽  
Author(s):  
Jianping Huang ◽  
Wenyuan Liao ◽  
Zhenchun Li
Keyword(s):  
Seismic Wave ◽  
Coordinate Transformation ◽  
Transformation Method ◽  
New Method ◽  
Content Type ◽  
Solid Interface ◽  
Viscoelastic Wave ◽  
Grid Scheme ◽  
Coordinate Transformation Method ◽  
Horizontal Interface

Purpose The purpose of this paper is to develop a new finite difference method for solving the seismic wave propagation in fluid-solid media, which can be described by the acoustic and viscoelastic wave equations for the fluid and solid parts, respectively. Design/methodology/approach In this paper, the authors introduced a coordinate transformation method for seismic wave simulation method. In the new method, the irregular fluid–solid interface is transformed into a horizontal interface. Then, a multi-block coordinate transformation method is proposed to mesh every layer to curved grids and transforms every interface to horizontal interface. Meanwhile, a variable grid size is used in different regions according to the shape and the velocity within each region. Finally, a Lebedev-standard staggered coupled grid scheme for curved grids is applied in the multi-block coordinate transformation method to reduce the computational cost. Findings The instability in the auxiliary coordinate system caused by the standard staggered grid scheme is resolved using a curved grid viscoelastic wave field separation strategy. Several numerical examples are solved using this new method. It has been shown that the new method is stable, efficient and highly accurate in solving the seismic wave equation defined on domain with irregular fluid–solid interface. Originality/value First, the irregular fluid–solid interface is transformed into a horizontal interface by using the coordinate transformation method. The conversion between pressures and stresses is easy to implement and adaptive to different irregular fluid–solid interface models, because the normal stress and shear stress vanish when the normal angle is 90° in the interface. Moreover, in the new method, the strong false artificial boundary reflection and instability caused by ladder-shaped grid discretion are resolved as well.

Cognitive Reflection Effects on Time Discounting

2018 ◽  
Vol 39 (2) ◽  
pp. 99-106 ◽  
Author(s):  
Michał Białek ◽  
Przemysław Sawicki
Keyword(s):  
Individual Differences ◽  
Individual Difference ◽  
Delay Discounting ◽  
Reference Point ◽  
Reference Points ◽  
Cognitive Reflection Test ◽  
Process Information ◽  
Time Discounting ◽  
Cognitive Reflection ◽  
The Way

Abstract. In this work, we investigated individual differences in cognitive reflection effects on delay discounting – a preference for smaller sooner over larger later payoff. People are claimed to prefer more these alternatives they considered first – so-called reference point – over the alternatives they considered later. Cognitive reflection affects the way individuals process information, with less reflective individuals relying predominantly on the first information they consider, thus, being more susceptible to reference points as compared to more reflective individuals. In Experiment 1, we confirmed that individuals who scored high on the Cognitive Reflection Test discount less strongly than less reflective individuals, but we also show that such individuals are less susceptible to imposed reference points. Experiment 2 replicated these findings additionally providing evidence that cognitive reflection predicts discounting strength and (in)dependency to reference points over and above individual difference in numeracy.

Functional stereotactic radiosurgery involving a dedicated linear accelerator and gamma unit: a comparison study

2004 ◽  
pp. 373-380 ◽  
Author(s):  
Timothy D. Solberg ◽  
Steven J. Goetsch ◽  
Michael T. Selch ◽  
William Melega ◽  
Goran Lacan ◽  
...  
Keyword(s):  
Stereotactic Radiosurgery ◽  
Linear Accelerator ◽  
Treatment Plan ◽  
Single Shot ◽  
Submillimeter Range ◽  
Primate Model ◽  
Content Type ◽  
Stereotactic Frame ◽  
Targeting Ability ◽  
Fine Print

Object. The purpose of this work was to investigate the targeting and dosimetric characteristics of a linear accelerator (LINAC) system dedicated for stereotactic radiosurgery compared with those of a commercial gamma knife (GK) unit. Methods. A phantom was rigidly affixed within a Leksell stereotactic frame and axial computerized tomography scans were obtained using an appropriate stereotactic localization device. Treatment plans were performed, film was inserted into a recessed area, and the phantom was positioned and treated according to each treatment plan. In the case of the LINAC system, four 140° arcs, spanning ± 60° of couch rotation, were used. In the case of the GK unit, all 201 sources were left unplugged. Radiation was delivered using 3- and 8-mm LINAC collimators and 4- and 8-mm collimators of the GK unit. Targeting ability was investigated independently on the dedicated LINAC by using a primate model. Measured 50% spot widths for multisource, single-shot radiation exceeded nominal values in all cases by 38 to 70% for the GK unit and 11 to 33% for the LINAC system. Measured offsets were indicative of submillimeter targeting precision on both devices. In primate studies, the appearance of an magnetic resonance imaging—enhancing lesion coincided with the intended target. Conclusions. Radiosurgery performed using the 3-mm collimator of the dedicated LINAC exhibited characteristics that compared favorably with those of a dedicated GK unit. Overall targeting accuracy in the submillimeter range can be achieved, and dose distributions with sharp falloff can be expected for both devices.

Lubricant compatibility of FKM seals in synthetic oils

2019 ◽  
Vol 72 (5) ◽  
pp. 557-565
Author(s):  
Dilek Bulut ◽  
Tatjana Krups ◽  
Gerhard Poll ◽  
Ulrich Giese
Keyword(s):  
Polyethylene Glycol ◽  
Design Methodology ◽  
Elevated Temperatures ◽  
Failure Mechanisms ◽  
Standard Test ◽  
New Method ◽  
Static Tests ◽  
Content Type ◽  
Lip Seals ◽  
First Results

Purpose Elastomer seals are used in many applications. They are exposed to lubricants and additives at elevated temperatures, as well as mechanical stresses. They can only provide good sealing function when they have resistance to those factors. There are many elastomer-lubricant compatibility tests based on DIN ISO 1817 in industry. However, they are insufficient and costly. Correlations between the tests and the applications are inadequate. The purpose of this study is investigating lubricant compatibility of fluoroelastomers (FKM) seals in polyethylene-glycol (PG)- and polyalphaolefin (PAO)- based synthetic oils and developing a methodology to predict seal service life. Design/methodology/approach A new compatibility test which is more sufficient in terms of time and cost was developed and compared with a standard test, currently used in industry. Compatibility of FKM radial lip seals with PG- and PAO-based synthetic oils with different additives was investigated chemically and dynamically. Failure mechanisms were examined. Findings The new method and the Freudenberg Flender Test FB 73 11 008 showed similar results concerning damages and similar tendencies regarding wear. The additive imidazole derivative was the most critical. Static tests give indications of possible chemically active additives, but alone they are insufficient to simulate the dynamic applications. Originality/value The paper describes a new method to investigate elastomer-lubricant compatibility and gives first results with a variety of lubricants.

Disposition effect at the market level: evidence from Indian stock market

2019 ◽  
Vol 12 (2) ◽  
pp. 69-82
Author(s):  
Sravani Bharandev ◽  
Sapar Narayan Rao
Keyword(s):  
Trading Volume ◽  
Stock Exchange ◽  
Reference Points ◽  
Disposition Effect ◽  
Content Type ◽  
Ex Post ◽  
Abnormal Trading Volume ◽  
The Difference ◽  
Trading Volumes ◽  
Indian Stock Market

Purpose The purpose of this paper is to test the disposition effect at market level and propose an appropriate reference point for testing disposition at market level. Design/methodology/approach This is an empirical study conducted on 500 index stocks of NSE500 (National Stock Exchange). Winning and losing days for each stock are calculated using 52-week high and low prices as reference points. To test disposition effect, abnormal trading volumes of stocks are regressed on their percentage of winning (losing) days. Further using ANOVA, the difference between mean of percentage of winning (losing) days of high abnormal trading volume deciles and low abnormal trading volume deciles is tested. Findings Results show that a stock’s abnormal trading volume is positively influenced by the percentage of winning days whereas percentage of losing days show no such effect. Findings are consistent even after controlling for volatility and liquidity. ANOVA results show the presence of high percentage of winning days in higher deciles of abnormal trading volumes and no such pattern in case of losing days confirms the presence of disposition effect. Further an ex post analysis indicates that disposition prone investors accumulate losses. Originality/value This is the first study, which proposes the use of 52-week high and low prices as reference points to test the market-level disposition effect. Findings of this study enhance the limited literature available on disposition effect in emerging markets by providing evidence from Indian stock markets.

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