# Water equivalent diameter

## Can the water-equivalent diameter be calculated from the central image?

Because patient dimension and attenuation can vary considerably along the longitudinal axis, the water-equivalent diameter be calculated for every slice or for all positions along that axis ( ). However, a previous study suggested that could be estimated from the central image in the scan range.

## Is it possible to calculate the water-equivalent diameter using all slices?

The calculation of water-equivalent diameter using all slices () gives an accurate result. However, it is not practical clinically because it requires a long time for calculation, especially in the case of modern CT scanners that produce more than 500 images (i.e., slices) for every examination.

## What is the difference between equivalent diameter and hydraulic diameter?

Note! – equivalent diameter is not the same as hydraulic diameter. The hydraulic diameter express the rate between the area section of the duct or tube, and the wetted perimeter of the duct or tube. Hydraulic diameter is used to determine if the flow is laminar or turbulent and to calculate the pressure loss.

## How to calculate equivalent diameter of duct?

The equivalent diameter of a rectangular tube or duct can be calculated as (Huebscher) de = 1.30 (a b)0.625 / (a + b)0.25 (1) where. de = equivalent diameter (mm, inches) a = length of major or minor side (mm, inches) b = length of minor or major side (mm, inches) Hydraulic diameter – the “characteristic length” used to calculate …

## What is water equivalent diameter?

The water-equivalent diameter (WED) is the diameter of a water cylinder with the same x-ray absorption as a specific patient and is used to determine absorbed dose (6,7) and to quantify patient size for the purpose of calculating SSDE (8).

## How do you find the equivalent diameter?

The equivalent diameter is given by deq = 4S/P, where S is the cross section and P the perimeter of the flow, L is the path length and ξ is a friction factor expressed as a function of Reynolds number and device geometry. Heat transfer and pressure drop calculations are interrelated.

## What is equivalent circle diameter?

The circular equivalent diameter, or area-equivalent diameter, is defined as the diameter of a circle with the same area as the particle. Thus, once the area of the particle, A, has been measured, the area-equivalent diameter (xA) can be calculated per Equation 3. It is most often expressed in units of m.

## What is meant by equivalent pipe?

An equivalent pipe is defined as the pipe of uniform diameter having loss of head and discharge equal to the loss of head and discharge of a compound pipe consisting of several pipes of different lengths and diameters.

## What is equivalent diameter of particle?

A concept used in evaluating the size of fine particles by a sedimentation process; it is defined as the diameter of a sphere that has the same density and the same freefalling velocity in any given fluid as the particle in question.

## How do you find the equivalent diameter of a square?

1:208:33Equivalent Diameter – Square Pitch vs Triangular Pitch – YouTubeYouTubeStart of suggested clipEnd of suggested clipAgain. So the equivalent diameter i just showed it is equal to four times four times the free areaMoreAgain. So the equivalent diameter i just showed it is equal to four times four times the free area divided by free area divided by the weighted perimeter weighted perimeter in this figure the free.

## What is equivalent diameter in sieve analysis?

Average equivalent diameter of particles = Tan θ5* D Where D is the diameter of the sample tube. After sizing silica sand by sieves, six samples were selected as shown in Table 1. Each of these samples was tested on the apparatus so as to calculate average equivalent diameter of particles.

## What is the equivalent diameter of a rectangular duct?

Rectangular equivalent diameter for air flows between 100 – 50000 cfm. The equivalent diameter is the diameter of a circular duct or pipe that gives the same pressure loss as an equivalent rectangular duct or pipe.

## What is the area and diameter of a cylinder of water referred to as?

The area and diameter of such a cylinder of water are referred to as the water equivalent area (A

## How to find the equivalent path length through water?

wis linearly dependent on the object attenuation, the equivalent path length through water can be found by normalizing the total attenuation by µ

## How to determine the overall water equiva- lent attenuation of the patient at a particular?

An estimate of the overall water equiva- lent attenuation of the patient at a particular position along the z-axis can be determined by summing the attenuation associated with each ray sample. That is, where the sum is taken over a horizontal line of a CT localizer radiograph. Having computed A

## What unit is used to calculate attenuation?

The attenuation values, or CT numbers, in the axial CT image are expressed using a special unit known as Hounsfield Units (HU): where µ(x,y)is the linear attenuation coefficient for a voxel in an axial CT image at position (x,y).

## How to calculate Wcan?

wcan be calculated using the mean CT number within a region of interest (ROI). The ROI must be large enough to include the entire patient cross section, but should not include irrelevant objects

## What is the DLP value?

vol) and dose length product (DLP) values are fre- quently used to represent radiation doses from a CT scan. The limitation of CTDI

## What is the equivalent diameter of a duct?

The equivalent diameter is the diameter of a circular duct or pipe that for equal flow gives the same pressure loss or resistance as an equivalent rectangular duct or pipe. A round shape results in lower pressure drops and less fan horsepower to move the air and, consequently, smaller equipment.

## What is hydraulic diameter?

Hydraulic diameter is used to determine if the flow is laminar or turbulent and to calculate the pressure loss. Fluid Mechanics – The study of fluids – liquids and gases. Involves velocity, pressure, density and temperature as functions of space and time.

## What is flat oval duct?

Flat oval ducts have smaller height requirements than round ducts and retain most of the advantages of the round ducts. Fittings for flat oval ducts are difficult to fabricate or modify in the field.

## Is equivalent diameter the same as hydraulic diameter?

Note! – equivalent diameter is not the same as hydraulic diameter. The hydraulic diameter express the rate between the area section of the duct or tube, and the wetted perimeter of the duct or tube. Hydraulic diameter is used to determine if the flow is laminar or turbulent and to calculate the pressure loss.

## Abstract

The purpose of this study is to accurately and effectively automate the calculation of the water-equivalent diameter () from 3D CT images for estimating the size-specific dose. is the metric that characterizes the patient size and attenuation. In this study, was calculated for standard CTDI phantoms and patient images.

## I. INTRODUCTION

CT dose is an important concept in the medical community, 1 – 4 especially due to the growing use of computed tomography (CT) examinations 5, 6 and concern over the relatively high dose from CT compared with other modalities. 7 – 9 There is an ongoing need to estimate the radiation dose from CT examinations accurately.

## II. MATERIALS AND METHODS

The objects for the calculations were standard CTDI phantoms (Leeds Test Objects (LTO) Medical Imaging Phantoms, Boroughbridge, UK) and patients. The phantoms consisted of two PMMA cylinders, one cylinder representing the head (16 cm diameter), and when nested inside the other representing the body (32 cm). The length of each cylinder was 14 cm.

## III. RESULTS

The results of contouring both automatically and manually are shown in Fig. 4. It can be seen visually that the results of automated contouring are similar to the manual contouring using free hand.

## IV. DISCUSSION

The aim of this study was to calculate the water-equivalent diameter () automatically from axial CT images. A number of authors have reported the calculation of the patient diameter. Cristianson et al.

## V. CONCLUSIONS

We have proposed and tested a new algorithm for the automated calculation of water-equivalent diameter ( ). The percentage differences of the automated results from the manual calculations were less than 0.5%, which is promising for the implementation of this method in the clinical environment.

## ACKNOWLEDGMENTS

The authors are grateful for the funding of this work by the Research and Innovation Program, Bandung Institute of Technology (ITB), No. 237h/I1.C01/PL/2015 and No. 006n/I1.C01/ PL/2016. The authors would like to thank Mr. Masdi from Prof. Dr. Margono Hospital, Purwokerto, Indonesia.