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Stone size calculator

With increasing frequency patients who present with kidney stones are undergoing computed tomography (CT) scans as an initial imaging study. Much of the management of kidney stones is based on stone size, but the same stone may appear larger on a conventional X-ray film (KUB) than on CT. The following Javascript calculator computes the apparent size of a kidney stone on KUB given the measured size on CT. Default values are given for the University of Illinois at Chicago KUB radiographic system (plate surface to film distance w is taken into account when measuring patient's dorsum to plate distance y2, hence the default value of 0 for w).

If you like, you may use Nakada's algorithm (Stephen Y. Nakada, Douglas G. Hoff, Sherwin Attai, Dennis Heisey, Donna Blankenbaker, and Myron Pozniak, "Determination of Stone Composition by Noncontrast Spiral Computed Tomography in the Clinical Setting", Urology 55 (6), 2000, pp. 816-819) to predict stone composition from Hounsfield unit density.

At the bottom of this page, you can download this calculator for a PalmPilot or Handspring device.

Diameter of stone on CT d1 = mm
X-ray source to plate distance p = cm
Stone to patient's dorsum distance y1 = cm
Patient's dorsum to plate distance y2 = cm
Plate surface to film distance w = mm
Maximum Hounsfield unit density =

Click here to download StoneCalc.prc, a PalmOS application for the PalmPilot or Handspring Visor device. (If you are using Netscape Navigator, and have trouble with this link, try clicking on it with the right mouse button, and choosing "Save Link As..." from the pop-up menu.)