MRI-based quantification of carbon and oxygen concentrations in human soft tissues for range verification in proton therapy

BACKGROUND

In-situ range verification of particle therapy based on the detection of secondary emitted radiation requires highly accurate assignment of elemental concentrations (particularly carbon and oxygen) in the human body.

PURPOSE

A method for quantitatively predicting carbon and oxygen concentrations in human soft tissues is proposed. This method relies on an empirical one-to-one correspondence between the mass fraction and water content (WC), which is a measurable tissue quantity based on magnetic resonance (MR) imaging (referred to as "MRWC-based method").

METHODS

A numerical analysis of the MRWC-based method was performed for 47 standard human soft tissues tabulated in the literature as objects of interest with unknown mass fractions of the four main elements-C, O, H, and N. Thereafter, the method was evaluated in terms of the mass-fraction quantification accuracy by comparing it with the gold-standard CT-based method developed by Schneider et al. The MRWC-based method was also applied to the MR imaging data of a virtual head phantom obtained from a three-dimensional MRI-simulated brain database.

RESULTS

The predicted mass fractions in a range of human soft tissues were in better agreement with the reference values than those predicted by the CT-based method. The mean absolute errors of the predicted mass% values for the overall standard soft tissues could be reduced from 4.8 percentage points (pp) (CT-based) to 0.5 pp (MRWC-based) for carbon and from 5.2 pp (CT-based) to 0.4 pp (MRWC-based) for oxygen. The application to the simulated MRI data confirmed the capability of the sufficient recognition of the boundaries between the white matter and gray matter in the brain that could not be realized by the CT-based method. Thus, the MRWC-based method exhibits superior performance in the prediction of carbon and oxygen concentrations in soft tissues.

CONCLUSIONS

This study is limited to a proof-of-concept scope but demonstrates the feasibility of the MRWC-based method for the generation of elemental images of human soft tissues from MRI-derived water-content images.

A herb is not just a small plant: what biomass allocation to rhizomes tells us about differences between trees and herbs

PREMISE

Biomass accumulation over years in vertical stems of trees leads to hypoallometric scaling between stem and leaf biomass within this growth form, while for herbaceous species, biomass allocation between these organ types typically exhibits isometry. However, biomass accumulation in herbs can occur in belowground perennating organs (e.g. rhizomes) that are, contrary to aboveground parts of herbs, long-lived. Although ecologically important, biomass allocation and accumulation in rhizomes (and similar organs) is mostly unknown.

METHODS

We assembled biomass investments into plant organs for 111 rhizomatous herbs based on a literature survey and greenhouse experiment. We estimated the proportion of whole plant biomass invested into rhizomes and, using allometric relationships, analyzed scaling between rhizome and leaf biomass and whether it is more variable than for other organs.

KEY RESULTS

On average, rhizomes comprise 30.2% total plant biomass. The proportion allocated to rhizomes does not change with plant size. Scaling between rhizome and leaf biomass is isometric and allocation to rhizomes is not more variable than allocation to other organs.

CONCLUSIONS

Rhizomatous herbs accumulate substantial biomass in rhizomes, and rhizome biomass is scaling isometrically with leaves, contrary to the hypoallometric relationship between stem and leaves in trees. This difference suggests that the rhizome biomass is in balance with aboveground biomass - a resource of carbon for rhizome formation that, at the same time, is dependent on carbon stored in rhizomes for its seasonal regrowth. This article is protected by copyright. All rights reserved.

Physical and elemental analysis of Middle East sands from recent combat zones

Objective: The lungs are uniquely exposed to the external environment. Sand and dust exposures in desert regions are common among deployed soldiers. A significant number of Veterans deployed to the Middle East report development of respiratory disorders and diseases.Materials and methods: Sand collected from Fallujah, Iraq and Kandahar, Afghanistan combat zones was analyzed and compared to a sand sample collected from an historic United States (U.S.) battle region (Fort Johnson, James Island, SC, Civil War battle site). Sand samples were analyzed to determine the physical and elemental characteristics that may have the potential to contribute to development of respiratory disease.Results: Using complementary scanning electron microscopy (SEM) imaging and analysis, and inductively coupled plasma mass spectrometry (ICP-MS), it was determined that Iraq sand contained elevated levels of calcium and first row transition metals versus Afghanistan and U.S. sand. Iraq sand particle texture was smooth and round, and particles were considerably smaller than Afghanistan sand. Afghanistan sand was elevated in rare earth metals versus Iraq or U.S. sands and had sharp edge features and larger particle size than Iraq sand.Conclusions: These data demonstrate significant differences in Iraq and Afghanistan sand particle size and characteristics. Middle East sands contained elevated levels of elements that have been associated with respiratory disease versus control site sand, suggesting the potential of sand/dust storm exposure to promote adverse respiratory symptoms. Data also demonstrate the potential for variation based on geographical region or site of exposure. The data generated provide baseline information that will be valuable in designing future exposure studies.

Averaging of Backscatter Intensities in Compounds

Low uncertainty measurements on pure element stable isotope pairs demonstrate that mass has no influence on the backscattering of electrons at typical electron microprobe energies. The traditional prediction of average backscatter intensities in compounds using elemental mass fractions is improperly grounded in mass and thus has no physical basis. We propose an alternative model to mass fraction averaging, based of the number of electrons or protons, termed "electron fraction," which predicts backscatter yield better than mass fraction averaging.