Lyu, Haiying, He, Naying, Wu, Bo, Trujillo, Paula, Yan, Fuhua, Lu, Yong, & Haacke, Ewart Mark. (2025). “Optimizing the visualization of the locus coeruleus using magnetization transfer contrast 3D imaging.” NeuroImage, 318, 121372. https://doi.org/10.1016/j.neuroimage.2025.121372
The locus coeruleus (LC) is a very small but important part of the brain that produces norepinephrine, a chemical that helps regulate attention, arousal, and stress responses. Problems with the LC are linked to diseases like Alzheimer’s and Parkinson’s, as well as some psychiatric disorders. However, because the LC is tiny and located deep in the brainstem, it is difficult to capture clear images of it using standard brain scans. This study worked to improve MRI methods to make fast, high-quality images of the LC possible in less than five minutes.
Researchers tested an optimized MRI scanning method, called a 3D gradient echo sequence with magnetization transfer contrast, on 11 healthy volunteers (6 younger adults and 5 older adults). They measured brain tissue properties, ran simulations to find the best scanning settings, and then collected MRI images. Two independent experts reviewed the images and measured how well the LC could be seen compared to surrounding tissue. The size and shape of the LC were also measured. Each participant was scanned multiple times over three days to check how consistent the results were.
In total, 98 scans were collected. The improved scanning method produced very clear, high-resolution images of the LC, showing strong contrast compared to surrounding tissue and consistent results between different raters and across repeated scans. The LC could be seen across several slices of the brain, with measurements showing it was about 2 mm wide on the left side and slightly smaller on the right.
In conclusion, this optimized MRI technique makes it possible to reliably capture detailed images of the LC in under five minutes. This provides a valuable new tool for studying brain health and disease in both clinical and research settings.
Fig. 1. Locus coeruleus (LC) MRI measurements. A) Illustration of the methods used to calculate the relative contrast ratio (rCR), contrast-to-noise ratio (CNR), and signal-to-noise ratio (SNR) of the LC. Circular regions of interest (ROIs) were manually placed over the bilateral LCs and the adjacent background area on image zoomed by a factor of 8 (zoom-in three times resulted in zoom factor of 23). To estimate regional noise, a subtraction image was generated by subtracting two repeated MTC scans acquired on the same day. The large red dashed ROI from the LC region (upper right of A) was copied onto the subtraction image (lower right of A) for noise estimation. B) Estimation of LC diameter using a diagonal line drawn across the LC, e.g., from the bottom left to the upper right, at approximately 45° on the zoomed image. This line extends through the LC and into the background region on the opposite side. The full width at half maximum (FWHM) and full width at quarter maximum (FWQM, 25%) were calculated to quantify LC dimensions, as shown on the right side of panel B.