Effect of dissolved organic nitrogen contamination on δ15 N-NH4 determination in water samples by modification of the diffusion method with gas-phase trapping.

RATIONALE: The isotopic tracer technique is widely used to identify the sources and fate of nitrogen (N) in order to understand the N cycle and contamination in water environments. The stable isotope ratio of ammonium is expected to greatly enhance the tracing analysis by combining it with the traditional nitrate isotope ratio. Diffusion followed by gas-phase trapping is the most commonly applied method for ammonium isotope ratio measurement. Although dissolved organic nitrogen (DON) is abundant in natural water and its breakdown in the diffusion procedure has been reported, the interference of DON with the measurement of ammonium isotope ratios has not been fully examined. METHODS: This study aims to test the effect of DON contamination by using organic N compounds, viz. humic acid and alanine. A series of diffusion experiments was conducted at a temperature of 80°C for a maximum of 7 days. Ammonia was transferred from alkaline solution and trapped with an acidic filter. This method was applied for samples with ammonium concentrations between 0.5 and 2.0 mg-N/L. RESULTS: There was no difference between the ammonium N stable isotope ratios for samples with and without added DON compounds; the fractionation between the observed value and the actual value was negligible, in the range of 0.2 to 1.0‰. The modifications of previous studies, i.e. shorter diffusion period, no vigorous shaking and using gas-phase trapping, successfully avoided any breakdown of DON in fresh water samples. CONCLUSIONS: The modified method provides high precision and accuracy and it is recommended for the analysis of anthropogenically influenced water samples, such as paddy fields, ground water, rivers and lakes.

Preoperative T staging of urinary bladder cancer: efficacy of stalk detection and diagnostic performance of diffusion-weighted imaging at 3T.

PURPOSE: We evaluated the ability of diffusion-weighted imaging (DWI) at 3 tesla for diagnosing T stage and detecting stalks in bladder cancer. METHODS: In total, 39 consecutive patients with bladder tumors underwent magnetic resonance (MR) imaging that included T2-weighted imaging (T2WI) and DWI using a 3T MR scanner. Two radiologists interpreted T2WI plus DWI and T2WI for diagnosis of T stage and for detection of stalks. We used McNemar's test to examine differences in diagnostic performance and Fisher's exact test to evaluate differences in stalk detection frequency. RESULTS: Specificity and accuracy in differentiating T1 tumors from T2 to T4 tumors were significantly better with T2WI plus DWI (83% [20/24] and 85% [33/39]) than T2WI (50% [12/24] and 67% [26/39]; P = 0.02), and accuracy for diagnosing tumor stage was significantly better with T2WI plus DWI (82% [32/39]) than T2WI alone (59% [23/39]; P = 0.03). The observers identified stalks in 11 tumors by T2WI (48% [11/23]) and 17 by DWI (74% [17/23]) (P < 0.03). CONCLUSION: DWI at 3T was superior to T2WI for evaluating the T stage of bladder cancer, particularly in differentiating T1 tumors from those T2 or higher, and in detecting stalks of papillary bladder tumors.

Utility of apparent diffusion coefficients in the evaluation of solid renal tumors at 3T.

PURPOSE: We assessed the usefulness of apparent diffusion coefficients (ADCs) for solid renal tumor imaging using diffusion-weighted magnetic resonance imaging (DWI) at 3T. METHODS: This retrospective study assessed ADCs of 31 patients with renal tumors that were imaged using preoperative DWI. DWI was performed with the b values of 50, 500, and 1000 s/mm(2), using a 3T magnetic resonance imaging (MRI) system (MAGNETOM Trio, 3T, Siemens Healthcare, Erlangen, Germany). The ADC map was calculated using the b values of 50 and 1000 s/mm(2). ADCs of the different tumors were compared according to the Tukey-Kramer test. RESULTS: The tumors were diagnosed as clear cell renal cell carcinoma (RCC; n = 20), papillary RCC (n = 1), infiltrating urothelial carcinoma (UC) of the kidney (n = 4), cystic RCC (n = 1), poorly differentiated carcinoma (n = 1), and angiomyolipoma (AML; n = 4). The mean ADC of clear cell RCC was significantly higher than that of infiltrating UC of the kidney (1.423 vs. 0.931 × 10(-3) mm(2)/s; P < 0.05), and the mean ADC of AML was significantly lower than that of clear cell RCC (0.674 vs. 1.423 × 10(-3) mm(2)/s; P < 0.01). CONCLUSION: ADCs used in DWI at 3T may be useful for differentiation of different types of solid renal tumors.

Diagnostic accuracy of ultra-high-b-value 3.0-T diffusion-weighted MR imaging for detection of prostate cancer.

PURPOSE: To investigate the diagnostic accuracy of 3.0-T diffusion-weighted imaging (DWI) for detection of prostate cancer by using different b-values. METHODS: Seventy-three patients underwent magnetic resonance imaging (MRI) at 3.0 T. Three MRI sets were reviewed by two radiologists: MRI and DWI (b = 500 s/mm(2)) (protocol A), MRI and DWI (b = 1000 s/mm(2)) (protocol B), and MRI and DWI (b = 2000s/mm(2)) (protocol C). Areas under the receiver operating characteristic curve (AUCs) were calculated. RESULTS: The mean of the AUCs in protocol C was larger than those in protocol A and in protocol B (P<.05). CONCLUSION: DWI (b = 2000s/mm(2)) at 3.0 T can improve the diagnostic accuracy for detection of prostate cancer.

MRI of the neck at 3 Tesla using the periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) (BLADE) sequence compared with T2-weighted fast spin-echo sequence.

PURPOSE: To evaluate motion artifacts, tissue contrasts, and lesion detectability in the neck with the periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) (BLADE) technique. MATERIALS AND METHODS: A total of 46 patients referred for MRI of the neck were included in a comparison of T2-weighted BLADE (T2W-BLADE) sequence and T2W fast spin-echo (T2W-FSE) sequence. All examinations were performed at 3T using the same parameters. Two observers evaluated unlabelled images for motion artifacts, the preferred image quality, and lesion detectability. Region of interest (ROI)-based quantitative measurements were performed to assess tissue contrasts. The frequency of occurrence of the different assessed artifacts and the lesion detectability was tested using McNemar's test. Tissue contrasts were compared using the Wilcoxon paired test. Reader agreement was assessed using kappa test. RESULTS: T2W-BLADE showed less ghosting and pulsation artifacts than T2W-FSE (P < 0.01). T2W-BLADE images were rated as better than or equal to T2W-FSE images in majority cases (93.5%; kappa = 0.64). There was not significant difference in tissue contrasts between T2W-BLADE and T2W-FSE. A total of 32 lesions were present in 32 patients and equally well seen on T2W-BLADE and T2W-FSE. CONCLUSION: T2W-BLADE can reduce motion artifacts and provide tissue contrasts and lesion detectability equivalent to T2W-FSE.