Intracellular water-specific MR of microbead-adherent cells: the HeLa cell intracellular water exchange lifetime

Quantitative characterization of tissue microstructure with temporal diffusion spectroscopy

The signals recorded by diffusion-weighted magnetic resonance imaging (DWI) are dependent on the micro-structural properties of biological tissues, so it is possible to obtain quantitative structural information non-invasively from such measurements. Oscillating gradient spin echo (OGSE) methods have the ability to probe the behavior of water diffusion over different time scales and the potential to detect variations in intracellular structure. To assist in the interpretation of OGSE data, analytical expressions have been derived for diffusion-weighted signals with OGSE methods for restricted diffusion in some typical structures, including parallel planes, cylinders and spheres, using the theory of temporal diffusion spectroscopy. These analytical predictions have been confirmed with computer simulations. These expressions suggest how OGSE signals from biological tissues should be analyzed to characterize tissue microstructure, including how to estimate cell nuclear sizes. This approach provides a model to interpret diffusion data obtained from OGSE measurements that can be used for applications such as monitoring tumor response to treatment in vivo.

Detection of apoptotic cell death in vitro in the presence of Gd-DTPA-BMA

Due to variability in patient response to cancer therapy, there is a growing interest in monitoring patient progress during treatment. Apoptotic cell death is one early marker of tumor response to treatment. Using known extracellular concentrations of gadolinium diethylenetriamine pentaacetic acid bismethylamide (Gd-DTPA-BMA) to vary the exchange regime, T(1) and T(2) relaxation data for acute myeloid leukemia (AML) cell samples were obtained and then analyzed using a two-pool model of relaxation with exchange. Leukemia cells treated with cisplatin to induce apoptosis exhibited a statistically significant (P < 0.05) decrease in intracellular longitudinal relaxation time, T(1I), from 1030 ms to 940 ms, a decrease (P < 0.001) in the intracellular water fraction, M(0I), from 0.86 to 0.68 and a statistically significant increase (P < 0.01) in transmembrane water exchange rate, k(IE), from 1.4 s(-1) to 6.8 s(-1). The changes in MR parameters correlated with quantitative histology, such as cellular cross-sectional area and average nuclear area measurements. The results of this study emphasize the importance of accounting for water exchange in dynamic contrast-enhanced MRI (DCE-MRI) studies, particularly those that examine tumor response to therapies in which apoptotic changes occur.

Diffusion-weighted MR imaging with background body signal suppression (DWIBS) for the diagnosis of malignant and benign breast lesions

The purpose of this study was to evaluate the efficacy of diffusion-weighted MR imaging with background body signal suppression (DWIBS) and a conventional DWI (cDWI) sequence for the detection of breast lesions. Fifty consecutive patients with suspected breast lesions underwent DWIBS and cDWI at 1.5 T. The routine protocol consisted of a short TI inversion recovery (STIR) sequence and a dynamic contrast-enhanced T1-weighted sequence. Apparent diffusion coefficient (ADC) and exponential ADC (eADC) values of the lesions were calculated. Receiver operating characteristic (ROC) analyses and qualitative evaluation of lesion detectability and conspicuity were performed. Thirty-six lesions were detected in 30 patients by using the routine protocol. DWIBS detected 34 lesions (94%) and cDWI detected 26 lesions (72%). The conspicuity of fibroadenomas was significantly (P = 0.007) better for DWIBS. ADC and eADC values of tumour were significantly different between DWIBS and cDWI. DWIBS is superior to cDWI in the visualization of malignant and benign lesions in the breast.

Intracellular water specific MR of microbead-adherent cells: HeLa cell intracellular water diffusion

The (1)H MR signal arising from flowing extracellular media in a perfused, microbead-adherent cultured cell system can be suppressed with a slice-selective, spin-echo pulse sequence. The signal from intracellular water can, thus, be selectively monitored. Herein, this technique was combined with pulsed field gradients (PFGs) to quantify intracellular water diffusion in HeLa cells. The intracellular water MR diffusion-signal attenuation at various diffusion times was well described by a biophysical model that characterizes the incoherent displacement of intracellular water as a truncated Gaussian distribution of apparent diffusion coefficients (ADCs). At short diffusion times, the water "free" diffusion coefficient and the surface-to-volume ratio of HeLa cells were estimated and were, 2.0 +/- 0.3 microm(2)/ms and 0.48 +/- 0.1 microm(-1) (mean +/- SD), respectively. At long diffusion times, the cell radius of 10.1 +/- 0.4 microm was inferred and was consistent with that measured by optical microscopy. In summary: 1) intracellular water "free" diffusion in HeLa cells was rapid, two-thirds that of pure water; and 2) the cell radius inferred from modeling the incoherent displacement of intracellular water by a truncated Gaussian distribution of ADCs was confirmed by independent optical microscopy measures.