PubMed · 8680316
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
D I Johnson. Using formulas and functions in spreadsheets.. https://pubmed.ncbi.nlm.nih.gov/8680316/
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
The objective of this present study was to develop a simple, easily understood methodology for solving biologically based models using a Microsoft Excel spreadsheet. The method involves the use of in-cell formulas in which Rows and Columns of new data are generated from data typed into the spreadsheet, but does not require any programming skills or use of the macro language. The approach involves entering the key parameter values into the spreadsheet and conducting the simulation by solving a set of equations based on these parameter values. The examples used in this paper are firstly, a simple voltage clamp simulation in which initial parameter values are used to calculate a system in steady state. The second example is a current clamp simulation where steady state is not reached and the solution of the equations for each time increment is used as the input for the next time increment in the simulation. The calculations are based on the Hodgkin Huxley mathematical equations that describe the voltage dependence of ion channel behavior. The problems and flexibility of the method are briefly discussed. The methodology developed in this present study should help novice modelers to create simple simulations without the need to learn a programming language or purchase expensive software.
BACKGROUND AND AIMS: In MR examinations of myocardial perfusion by the use of Snapshot-FLASH sequences it is of major importance that the achievable signal difference between pre- and normal postcontrast myocardium be maximized. METHODS: In ECG-triggered Snapshot-FLASH sequences the signal intensity of the myocardium depends on the flip angle alpha, the inversion time TI and the trigger delay TD (both depending on the cardiac frequency f) for unchanged slice thickness (SL), matrix size (MA), repetition time (TR) and echo time (TE). Therefore a simulation of the signal behavior of pre- and postcontrast myocardium based on Bloch's equations was performed by varying the flip angle alpha, TI and TD for different cardiac frequencies in order to determine an optimized combination of the measurement parameters. RESULTS: In normal heart rates (50-70 beats/min) maximal signal differences between pre- and normal postcontrast myocardium can be reached for inversion times TI = 170-200 ms and a flip angle alpha = 11 degrees. For higher heart rates again alpha = 11 degrees and TI = 200-220 ms with shortened TD (TD = 0 for f > 90 beats/min) were found to be optimal. The calculated values were semiquantitatively confirmed in phantom and volunteer measurements. CONCLUSIONS: The described method allows cardiac frequency dependent optimization of the Snapshot-FLASH measurement parameters alpha, TI and TD in order to reach a maximum in signal contrast between normal and malperfused myocardium.
We developed a pre-operative simulation and intra-operative navigation system with three-dimensional computer graphics (3D-CG). Because the 3D-CG created by the present system enables visualization of lesions via semitransparent imaging of the scalp surface and brain, the expected operative field could be visualized on the computer display pre-operatively. We used two different configurative navigators. One is assembled by an arciform arm and a laser pointer. The arciform arm consists of 3 joints mounted with rotary encoders forming an iso-center system. The distal end of the arm has a laser pointer, which has a CCD for measurement of the distance between the outlet of the laser beam, and the position illuminated by the laser pointer. Using this navigator, surgeons could accurately estimate the trajectory to the target lesion, and the boundaries of the lesion. Because the other navigator has six degrees of freedom and an interchangeable probe shaped like a bayonet on its tip, it can be used in deep structures through narrow openings. Our system proved efficient and yielded an unobstructed view of deep structures during microscopic neurosurgical procedures.