Biomedical subjects

Akintunde Akangbe Okunade

Publications and source records attributed to Akintunde Akangbe Okunade.

8 recordsLinked to original sources

PubMed2006

Method for the evaluation of a average glandular dose in mammography.

This paper concerns a method for accurate evaluation of average glandular dose (AGD) in mammography. At different energies, the interactions of photons with tissue are not uniform. Thus, optimal accuracy in the estimation of AGD is achievable when the evaluation is carried out using the normalized glandular dose values, g(x,E), that are determined for each (monoenergetic) x-ray photon energy, E, compressed breast thickness (CBT), x, breast glandular composition, and data on photon energy distribution of the exact x-ray beam used in breast imaging. A generalized model for the values of g(x,E) that is for any arbitrary CBT ranging from 2 to 9 cm (with values that are not whole numbers inclusive, say, 4.2 cm) was developed. Along with other dosimetry formulations, this was integrated into a computer software program, GDOSE. FOR, that was developed for the evaluation of AGD received from any x-ray tube/equipment (irrespective of target-filter combination) of up to 50 kVp. Results are presented which show that the implementation of GDOSE. FOR yields values of normalized glandular dose that are in good agreement with values obtained from methodologies reported earlier in the literature. With the availability of a portable device for real-time acquisition of spectra, the model and computer software reported in this work provide for the routine evaluation of AGD received by a specific woman of known age and CBT.

Algorithms↗

PubMed2005

Effective dose as a limiting quantity for the evaluation of primary barriers for diagnostic x-ray facilities.

The National Council on Radiation Protection in Report 147 of NCRP has recommended that shielding design limit for diagnostic x-ray facilities must be consistent with the guidance specified in Report 116 of NCRP. In the latter report, it is specified that the limit of exposure must be in terms of effective dose received annually. New mathematical models that are different from those in Report 49 of NCRP are reported in the recently published Report 147 of NCRP, and the design limit is specified as kerma value. In this work, to provide a means of compliance with the recommendation in Report 116 of NCRP, the effective dose that is classified as the limiting quantity in Report 57 of ICRU has been incorporated into shielding algorithms for diagnostic x-ray facilities. Also, shielding models are presented using exposure, kerma-in-air, kerma-in-tissue and ambient dose equivalent as limiting quantities. A computer program, XSHIELD, was written in FORTRAN language to execute these models. With design limits set at 1 mSv y and 0.25 mSv y (as specified in Report 116 of NCRP) and using sample distribution of workload, age of patient, field sizes at image receptor, and types of projection, computations of shielding requirements were carried out for rooms designated adult and pediatric chest rooms. For same values of respective workload and design limit, the use of exposure, kerma-in-air, kerma-in-tissue, and ambient dose equivalent as limiting quantity produces thicker barriers than the use of effective dose. By the use of effective dose as limiting quantity, the shielding requirement for the same workload is independent of size of the individual to be shielded. However, irradiating the individual who is to be shielded in posterior-anterior projection requires a thicker barrier than when irradiation is in lateral projection.

Adolescent↗

PubMed2005

Evaluation of lead equivalence of patient and hardware materials in medical diagnostic x-ray shielding.

In the estimation of additional shielding requirements for primary beam apart from that provided by patient and hardware in the x-ray beam, there is the need to distinguish between attenuation and hardening properties of materials in comparison. In this work, numerical comparison of attenuation and hardening properties of phantom (Lucite, soft tissue, water) and hardware (aluminum and steel) materials with those of lead have been carried out. Results presented show that the shielding affordable by lead attenuation equivalent thicknesses (LAE) and lead hardening equivalent thicknesses (LHE) is not strictly equivalent to that affordable by thicknesses of substitutes (phantom materials, aluminum and steel) when there are differences in attenuation and hardening properties. Even though beams through LAE that are not "exact" have equal exposure values, the half value layers are higher than those through thicknesses of lead substitutes. Example calculations show that the use of lead thickness (LAE) that are not "exact" to account for the shielding afforded by the thickness of the patient (water phantom) produces lesser reduction of the primary radiation level in the area indicated for shielding. The "exact" LAE that will reduce the primary radiation level equally as the patient and radiographic table may be higher by close to 20% or more of that which is not "exact."

Aluminum↗

PubMed2005

Comparative study of the influence of anode and filter materials on primary shielding requirements for mammography.

Comparison of primary shielding requirements for mammography x-ray beams that are transmitted through different filter materials at equivalent thicknesses has been carried out. In this study, the primary shielding requirement is that which is additional to that provided by the compression paddle, breast tissue, grid and image receptor. Equivalent thickness is defined as the thickness of a filter material (with Z-value between 37 and 55) that will reduce either intensity or total energy or exposure of a given unfiltered incident beam by the same extent or produce equal hardening of the same unfiltered beam as a reference filter (0.03 g cm Mo). The unfiltered incident beams used are those generated by molybdenum (Mo) and tungsten (W) anodes at kVp's of 18, 20, 22,..,42. In most cases (especially for filter with Z-values greater than 42 and values of operating potential greater than 22 kVp), results show that no single thickness was found that could simultaneously match intensity, total energy, exposure, and hardening as the reference filter. There are significant disparities in the values of the additional primary shielding requirements for beams transmitted through the equivalent thicknesses. Structures of the computer software programs (MAFHAMS and MAXRAPS) used to execute the models developed for the computations of the additional primary shielding requirements for the 'equalized' beams are presented.

Algorithms↗

PubMed2005

Parameterized algorithms for quantitative differentials in spectrally equivalent medical diagnostic x-ray beams.

Qualitative and quantitative equivalence of spectra transmitted by two different elemental filters require a good match in terms of shape and size over the entire energy range of 0-150 keV used in medical diagnostic radiology. However, the photoelectric absorptions and Compton scattering involved in the interaction of x rays with matter at these relatively low photon energies differ in a nonuniform manner with energy and atomic number. By careful choice of thicknesses for filter materials with an atomic number between 12 and 39, when compared with aluminum, it is possible to obtain transmitted beams of the same shape (quality) but not of the same size (quantity). In this paper, calculations have been carried out for the matching of the shapes and sizes of beams transmitted through specified thicknesses of aluminium filter and spectrally equivalent thicknesses of other filter materials (different from aluminium) using FORTRAN source codes traceable to the American Association of Physics in Medicine (AAPM), College Park, MD, USA. Parametrized algorithms for the evaluation of quantitative differentials (deficit or surplus) in radiation output (namely, photon fluence, exposure, kerma, energy imparted, absorbed dose, and effective dose) from these transmitted spectrally equivalent beams were developed. These differentials range between 1%, and 4% at 1 mm Al filtration and between 8%, and 25% for filtration of 6 mm Al for different filter materials in comparison with aluminum. Also developed were models for factors for converting measures of photon fluence, exposure-area product, (EAP), and kerma-area product (KAP) to risk related quantities such as energy imparted, absorbed dose, and effective dose from the spectrally equivalent beams. The thicknesses of other filter materials that are spectrally equivalent to given thicknesses of aluminum filter were characterized using polynomial functions. The fact that the use of equivalent spectra in radiological practice can provide means of ranking the differentials in radiographic image quality and stochastic risk is discussed.

Algorithms↗

PubMed2004

Numerical models for the determination of primary structural barriers for diagnostic x-ray facilities.

In this work, numerical models are presented for the determination of additional shielding requirements apart from that afforded by patient and hardware devices (grid, cassette, cassette holder, and x-ray table) for diagnostic x-ray primary beams. The models provide an opportunity for the incorporation of appropriate transmission factors obtained by integration of incident radiation energy distribution and workload spectra for clinically realistic condition of varying thicknesses of patient. It was found that as a result of significant differences in the attenuation and hardening properties of water (which was used to represent patient) and lead, lead exposure attenuation equivalent thicknesses do not transmit beam of equivalent penetrating power (though of equivalent exposure) as corresponding patient thicknesses. Sample results are presented which show that ignoring these significant differences will result in underestimation of shielding afforded by patient and hardware devices in practice; thus installing in addition more thickness of lead than necessary. For different incident beam qualities (kVp), obtaining exposure attenuation equivalence of varying thicknesses of patients and hardware in terms of lead is a nontrivial phenomenon.

Humans↗

PubMed2004

Determination of shielding requirements for mammography.

Shielding requirements for mammography when considerations are to be given to attenuation by compression paddle, breast tissue, grid and image receptor (intervening materials) has been investigated. By matching of the attenuation and hardening properties, comparisons are made between shielding afforded by breast tissue materials (water, Lucite and 50%-50% adipose-glandular tissue) and some materials considered for shielding diagnostic x-ray beams, namely lead, steel and gypsum wallboard. Results show that significant differences exist between the thickness required to produce equal attenuation and that required to produce equal hardening of a given incident beam. While attenuation equivalent thickness produces equal exposure, it does not produce equal hardening. For shielding purposes, equivalence in exposure reduction without equivalence in penetrating power of an emerging beam does not amount to equivalence in shielding affordable by two different materials. Presented are models and results of sample calculations of additional shielding requirements apart from that provided by intervening materials. The shielding requirements for the integrated beam emerging from intervening materials are different from those for the integrated beam emerging from materials (lead/steel/gypsum wallboard) with attenuation equivalent thicknesses of these intervening materials.

Body Burden↗

PubMed2002

Comparison of lead attenuation and lead hardening equivalence of materials used in respect of diagnostic X-ray shielding.

Present interest is in the shielding of diagnostic X-ray units. Numerical comparison has been made of the attenuation and hardening properties of lead and some particular alternative materials: steel, plate glass and gypsum wallboard. Results show, for particular choices of thickness, that lead and steel can be made to provide closely similar attenuation and spectral hardening, values of lead attenuation equivalent (LAE) and lead hardening equivalent (LHE) thicknesses being nearly the same. Significant differences in the attenuation and hardening properties of lead are found in comparison with plate glass and gypsum wallboard. LAE produces better matching of exposure for lead-plate glass and lead-gypsum wallboard than LHE.

Diagnostic Imaging↗