Biology subjects

Nanga, R. P. R.

Publications and source records attributed to Nanga, R. P. R..

4 recordsLinked to original sources

bioRxiv2026

Contrast-induced changes in chemical exchange saturation transfer MRI differentiate tumor progression from pseudoprogression

Tumor pseudo-progression (PsP) refers to an initial increase in tumor size or the appearance of new lesions. These pseudo-progressive lesions are predominantly composed of infiltrative inflammatory cells, such as macrophages. This phenomenon commonly occurs in patients undergoing radiation therapy or immunotherapy and typically indicates a positive treatment response. However, it often leads to premature treatment cessation due to misinterpretation as disease progression. Non-invasive imaging biomarkers capable of distinguishing pseudo-progression from true progression would greatly aid in treatment decision-making. In our preliminary study, we explored the potential of gadoterate meglumine (Gd-DOTA, a macrocyclic Gd-contrast) in combination with amine chemical-exchange saturation transfer (amine-CEST) imaging to differentiate tumor from radiation necrosis by assessing Gd-DOTA uptake by infiltrating immune cells, such as macrophages. To evaluate whether amine-CEST, in combination with Gd-DOTA, can differentiate macrophages from cancer cells, we incubated them with Gd-DOTA for 30 minutes. Subsequently, the cells were processed, and amine-CEST imaging was performed on a 9.4 Tesla preclinical scanner. Upon treatment with Gd-DOTA, we did not observe a significant change in amine-CEST contrast in F98 cells compared with untreated cells, whereas treated macrophages exhibited a marked decrease ([~]40%) in amine-CEST signal compared with untreated macrophages. This reduction in signal was attributed to the uptake of Gd-DOTA by macrophages, which notably shortened water T1 relaxation, thereby quenching the amine-CEST signal. Conversely, cancer cells showed no appreciable change in the amine-CEST signal, indicating no Gd-DOTA uptake. Furthermore, to validate that T1 shortening influences amine-CEST signal, cancer cells were also treated with manganese chloride (MnCl2) for 30 minutes. The uptake of MnCl2 by cancer cells similarly induced T1 shortening, as observed in macrophages, resulting in a decrease in the amine-CEST signal from these cells. Next, we performed the amin-CEST imaging on F98 tumor-bearing rats and radiation necrotic rats. Post-injection with Gd-DOTA showed no appreciable change in the amine-CEST contrast in the tumor-bearing rat, whereas a significant decrease in contrast was observed in the radiation necrotic rat. This further demonstrates that no change in the amine-CEST contrast in tumor-bearing rats is due to cancer cells failing to take up Gd-DOTA. The decrease in amine-CEST contrast in radiation-treated rats reflects the uptake of Gd-DOTA by macrophages infiltrating the radiation-necrotic regions. This straightforward imaging approach holds promise for clinical translation. It offers a novel method for characterizing pseudo-progressive lesions and monitoring diverse treatment responses in cancer patients using standard clinical scanners.

cancer biology↗

bioRxiv2025

Multimodal MR Imaging for quantification of brain lipid in mice at 9.4T

BackgroundAdvanced MR imaging techniques like steady state Nuclear Overhauser enhancement (ssNOE), transient NOE (tNOE), and myelin water fraction (MWF) provide a non-invasive way to assess the biochemical and structural integrity of brain tissue. Their sensitivity to endogenous lipids and macromolecules allows for the early detection of neuropathological changes, making them valuable tools in studying brain health and disease progression. In this study, we systematically evaluate the repeatability and sensitivity of NOEMTR, tNOE, and MWF for quantifying lipid and myelin content in the brains of wild-type (WT) mice, correlating the results with immunohistochemistry (IHC). MethodsFive 6-month-old C57BL6/J mice were imaged using 3D-NOE, and four mice underwent imaging with 2D tNOE and MWF across four repeated sessions using a 9.4T Scanner. For ssNOE imaging, CEST-weighted images at 56 frequency offsets were acquired using B1rms of 1.0 T and 3s saturation duration. For tNOE, 52 offsets were acquired with a hyperbolic secant inversion pulse (bandwidth = 400Hz, duration = 44ms) and a mixing time of 200ms. For MWF, a multi-echo spin-echo (MESE) sequence was acquired with 40 evenly spaced echoes from 5.5ms to 200ms. For both ssNOE and tNOE, B0 correction was performed using WASSR. Repeatability was quantified using intra- and inter-subject coefficients of variation (COV%). Pearson correlation was performed to see the association between imaging matrices and IHC measures, Luxol fast blue (LFB) stained sections, and myelin basic protein (MBP). ResultsAll techniques demonstrated high repeatability across the whole brain (WB) and selected regions of interest (ROIs). Whole-brain intra-subject COV% for NOEMTR ranged from 1.92% to 3.40%, with corresponding inter-subject COVs of 1.50%. tNOE exhibited improved intra-subject repeatability with COVs ranging from 0.75% to 5.57%, but a reduced inter-subject COV of 2.97%. MWF imaging showed the highest stability overall, with an intra-subject COV ranging from 0.47% to 2.03% and an inter-subject COV of 0.75%. Visually, tNOE offers superior contrast in myelin-rich areas compared to NOEMTR and MWF imaging, showing greater sensitivity to myelinated regions. tNOE strongly correlates with histological markers: r = 0.83 with MBP staining and r = 0.72 with LFB staining (both p < 0.001). MWF and NOEMTR showed correlations with MBP (r = 0.63 and r = 0.57, respectively). ConclusionNOEMTR, tNOE, and MWF imaging are reliable and repeatable methods for quantifying macromolecules in the brain. Among these, tNOE emerges as the most sensitive for detecting myelin lipids as confirmed by histological validation. These findings highlight the translational potential of tNOE for studying demyelinating disorders and neurodegenerative diseases.

neuroscience↗

bioRxiv2025

Magnetic Resonance Imaging for Improved Brain Tumor Detection

Precise demarcation of brain tumor boundaries is critical for optimizing treatment strategies and improving patient outcomes. In vivo characterization of tumor using PET/CT and MRI is clinical standard. PET/CT highlights the metabolic aspects of the tumor, while MRI provides information on functional, metabolic and structural changes. Even with technological advancements in both PET/CT and MRI, a method that can precisely delineate infiltrative tumor boundaries from normal-appearing brain regions (NABR) in vivo is still lacking. To address this limitation, we explored a relatively new MR imaging method, the Nuclear Overhauser Effect Magnetization Transfer Ratio (NOEMTR), in conjunction with a gadolinium-based contrast agent (Gd-DOTA), to precisely delineate the tumor boundaries in a rat model of infiltrative gliosarcoma. NOEMTR imaging was performed in the rat model (n=5) before and after Gd-DOTA administration. The post-Gd-DOTA NOEMTR map was subtracted from the pre-Gd-DOTA map and compared with contrast-enhanced T1-weighted images and immuno-histological findings. The resulting NOEMTR difference map clearly highlighted both the tumor core and infiltrative boundaries, which was not discernible on the post-contrast T1-weighted images. The extended tumor boundaries observed on the NOEMTR difference map corroborated with the IHC image, which confirmed the presence of infiltrative tumor cells and macrophages in these regions. Guided by the NOEMTR difference map, regions of interest (ROI) were drawn to quantify NOEMTR signal changes in the tumor core, tumor boundaries, and NABR post-Gd-DOTA. Tumor core showed a significant [~]43% reduction in NOEMTR signal (plJ=lJ0.003), while the tumor periphery exhibited a moderate reduction of [~]10%, (plJ=lJ0.045). No appreciable change in was observed in the NABR (plJ=lJ0.371). In contrast, the post contrast T1-weighted signal changes in tumor core, tumor periphery and NABR were, 33.32% (p = 0.092), 3.8% (p = 0.478), and 8.7% (p = 0.464) respectively. These findings suggest that NOEMTR imaging provides enhanced tumor contrast, particularly at the infiltrative tumor margins, where conventional contrast enhanced T1-weighted MRI may underestimate tumor extent. Histological validation confirmed the presence of infiltrative tumor cells and macrophages in the tumor periphery, as highlighted by the NOEMTR difference map. Overall, NOEMTR imaging, in combination with Gd-DOTA administration, demonstrates superior delineation of brain tumor boundaries compared to conventional MRI. As NOEMTR imaging is a fast acquisition scan (under 10 minutes) and performed on standard 3 Tesla, it can be easily integrated into clinical protocols. By improving visualization of tumor infiltration and distinguishing tumor regions from NABR, NOEMTR imaging holds promise for advancing neuro-oncological diagnostics and treatment planning.

bioengineering↗

bioRxiv2024

Quantification of NAD+ T1 and T2 relaxation times using downfield 1H MRS at 7 T in human brain in vivo

IntroductionThe purpose of this study was to use a single-slice spectrally-selective sequence to measure T1 and T2 relaxation times of NAD+ proton resonances in the downfield 1H MRS spectrum in human brain at 7 T in vivo and assess the propagation of relaxation time uncertainty in NAD+ quantification. MethodsDownfield spectra from 7 healthy volunteers were acquired at multiple echo times in all subjects to measure T2 relaxation, and saturation recovery data were to measure T1 relaxation. The downfield acquisition used a spectrally-selective 90{degrees} sinc pulse for excitation centered at 9.1 ppm with a bandwidth of 2 ppm, followed by a 180{degrees} spatially-selective Shinnar-Le Roux refocusing pulse for localization. For the multiple echo experiment, spectra were collected with echo times ranging from 13 to 33 ms. For the saturation recovery experiment, saturation was performed prior to excitation using the same spectrally-selective sinc pulse as was used for excitation. Saturation delay times (TS) ranged from 100 to 600 ms. Uncertainty propagation analysis was performed analytically and with Monte Carlo simulation. ResultsThe mean {+/-} standard deviation of T1 relaxation times of the H2, H6, and H4 protons were 152.7 {+/-} 16.6, 163.6 {+/-} 22.3, and 169.9 {+/-} 11.2 ms, respectively. The mean {+/-} standard deviation of T2 relaxation times of the H2, H6, and H4 protons were 32.5 {+/-} 7.0, 27.4 {+/-} 5.2, and 38.1 {+/-} 11.7 ms, respectively. The mean R2 of the H2 and H6 T1 fits were 0.98. The mean R2 of the H4 proton T1 fit was 0.96. The mean R2 of the T2 fits of the H2 and H4 proton resonances were 0.98, while the mean R2 of the T2 fits of the H4 proton was 0.93. The relative uncertainty in NAD+ concentration due to relaxation time uncertainty was 8.5%-11%. ConclusionUsing downfield spectrally-selective spectroscopy with single-slice localization, we found NAD+ T1 and T2 relaxation times to be approximately 162 ms and 32 ms respectively in the human brain in vivo at 7 T.

bioengineering↗