You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["AnatomicalEntity"].

Please return the output as a JSON object of the format: {"AnatomicalEntity": ["tumor cells", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Determination of As metabolites
We assessed As metabolism using the percentages of iAs, MMA, and DMA in urine, as well as two methylation indexes [i.e., primary methylation index (PMI), defined as the ratio between MMA and iAs, and secondary methylation index (SMI), defined as the ratio between DMA and MMA. We used total urinary As [U-As; the sum of As metabolites (iAs + MMA + DMA) in urine] as the measure of iAs exposure. Concentrations of As metabolites in urine were measured with an Agilent 1100 HPLC system (Agilent Technologies, Waldbronn, Germany), coupled with hydride generation (HG) inductively coupled plasma mass spectrometry (ICPMS) (Agilent 7500ce series; Agilent Technologies, Japan). The method measures metabolites of iAs [iAs(III), iAs(V), MMA, and DMA], but not organic As species (e.g., arsenobetaine, arsenocholine) originating from the diet, because those arsenicals do not form volatile arsines (hydride generation) like iAs and its metabolites do. The method was described in detail by Lindberg et al. (2006). Determination limits were 0.1 mug/L for arsenite [As(III)] and MMA and 0.2 mug/L for DMA and arsenate [As(V)]. We adjusted As concentrations for variations in dilution by specific gravity (to the mean value of 1.012 g/mL); U-Cre, which is commonly used for dilution adjustment, was influenced more by age and nutrition than was specific gravity, and U-Cre was also associated with urinary As (Nermell et al. 2007).
For quality control purposes, we analyzed the reference material (CRM No. 18; National Institute for Environmental Studies, Ibaraki, Japan) with a certified DMA concentration of 36 +/- 9 mug/L together with the collected urine samples. The concentration of DMA was 41 +/- 3.4 mug/L (mean +/- SD; n = 18). Urine samples were also analyzed for As metabolites by atomic fluorescence spectrometry (AFS) and for the sum of As metabolites by atomic absorption spectrometry (AAS), as reported by Lindberg et al. (2007a). The results of ICPMS and AFS showed good agreement for all metabolites; for iAs [As(III) + As(V)], MMA, and DMA, R2 = 0.91, 0.91, and 0.97, respectively (n = 221). Further, we obtained good agreement for the sum of As metabolites between the three different methods (for ICPMS vs. AFS, R2 = 0.97; for ICPMS vs. AAS, R2 = 0.96 (n = 221).
{"AnatomicalEntity": ["urine samples", "urine", "plasma", "Urine samples", "urinary"]}