Dose Profile and Dose Index Analysis in Computed Tomography

Oliveira, A.D.; Alves, José L. D.; Carvalho, Alexandra; Carreiro, J.V.

doi:10.1093/oxfordjournals.rpd.a082566

Cited by 3 publications

(6 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…SSDPs measured in PMMA phantoms have previously been modeled as the sum of two Gaussians, 6 a combination of a Gaussian and a Lorentzian, 20 and a product of exponentials. 27 We found the sum of two modified Gaussians and an asymmetry term (see Appendix A) work best for modeling the raw SSDPs in the plasticwater phantom. The solid curves in Figs.…”

Section: B Single Scan Dose Profilesmentioning

confidence: 94%

See 1 more Smart Citation

Novel methods of measuring single scan dose profiles and cumulative dose in CT

2004

View full text Add to dashboard Cite

Computed tomography dose index (CTDI) is a conventional indicator of the patient dose in CT studies. It is measured as the integration of the longitudinal single scan dose profile (SSDP) by using a 100-mm-long pencil ionization chamber and a single axial scan. However, the assumption that most of the SSDP is contained within the chamber length may not be valid even for thin slices. We have measured the SSDPs for several slice widths on two CT scanners using a PTW diamond detector placed in a 300 mm x 200 mm x 300 mm water-equivalent plastic phantom. One SSDP was also measured using lithium fluoride (LiF) TLDs and an IC-10 small volume ion chamber, verifying the general shape of the SSDP measured using the diamond detector. Standard cylindrical PMMA CT phantoms (140 mm length) were also used to qualitatively study the effects of phantom shape, length, and composition on the measured SSDP. The SSDPs measured with the diamond detector in the water-equivalent phantom were numerically integrated to calculate the relative accumulated dose D(L)(0)calc at the center of various scan lengths L. D(L)(0)calc reached an equilibrium value for L > 300 mm, suggesting the need for phantoms longer than standard CT dose phantoms. We have also measured the absolute accumulated dose using an IC-10 small volume ion chamber, D(L)(0)SV, at three points in the phantom cross section for several beamwidths and scan lengths. For one CT system, these measurements were made in both axial and helical scanning modes. The absolute CTDI100, measured with a 102 mm active length pencil chamber, were within 4% of D(L)(0)SV measured with the small volume ion chamber for L approximately 100 mm suggesting that nonpencil chambers can be successfully used for CT dosimetry. For nominal beam widths ranging from 3 to 20 mm and for L approximately 250 mm, D(L)(0)SV values at the center of the water-equivalent phantom's elliptic cross section were approximately 25%-30% higher than the measured CTDI100. For small beamwidths, the difference in D(L)(0)SV for L approximately 250 mm and L approximately 14 x beamwidth (CTDI14nT) reached up to 50%. Peripheral point doses at 70 mm depth along the major axis of the phantom for L approximately 250 mm were up to 22% higher than for L approximately 100 mm. The differences between CTDI100 and D(L)(0)SV for L approximately 250 mm were in good agreement with the predictions made from the numerical integration of the measured SSDPs. Due to the considerable dose measured beyond the length of standard CT phantoms, CT dosimetry for longer body scan series should be performed in longer phantoms. Measurements could be made as we have shown, using a small volume chamber translating through the beam using multiple scans.

show abstract

Section: B Single Scan Dose Profilesmentioning

confidence: 94%

“…25 The inclusion of an imaging parameter ͑T͒ in a dosimetric quantity has previously been identified as problematic 23,26 and a potentially large source of error since the FWHMs of the sensitivity profile and SSDP can greatly differ. 19,27 Practical variations of CTDI commonly used are CTDI 100 (Refs. 8 and 9) and CTDI 14T (Ref.…”

Section: A Ctdimentioning

confidence: 99%

Novel methods of measuring single scan dose profiles and cumulative dose in CT

2004

View full text Add to dashboard Cite

show abstract

“…Others have argued that the using the FWHM is more appropriate that the collimation nT in the CTDI formula. Oliveira et.al [6] defined where nT is replaced by the FWHM, while Dixon and…”

Section: C4 Extension Of the Theory To Scbctmentioning

confidence: 99%

“…Beside this definition of the dose index, there were also mathematical descriptions of the dose profile produced by a CT beam in a phantom. These involved the use of a double Gaussian function [2], of Gaussian and Lorentzian functions [3,4], purely Gaussian function [5], and an exponential function [6]. Furthermore, a mathematical model that described the scatter contribution to the beam profile as a two-dimensional convolution between a primary function and an unknown blurring function was developed by Gagne in 1989 [3].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

A model of CT dose profiles in Banach space; with applications to CT dosimetry

Weir

2016

Phys. Med. Biol.

View full text Add to dashboard Cite

In this paper the scatter component of computed tomography dose profiles is modeled using the solution to a nonlinear ordinary differential equation. This scatter function is summed with a modeled primary function of approximate trapezoidal shape. The primary dose profile is modeled to include the analytic continuation of the Heaviside step function. A mathematical theory is developed in a Banach space. The modeled function is used to accurately fit data from a 256-slice GE Revolution scanner. A 60 cm long body phantom is assembled and used for data collection with both a pencil chamber and a Farmer-type chamber.

show abstract