Background: N-Acetylaspartate (NAA) is a key biomarker linked to memory and neurodegeneration. Previous studies have looked at the consistency of reliably measuring hippocampal NAA by using the coefficients of variation, but have not addressed Intraclass Correlation Coefficient (ICC), which is critical for determining whether the measure can reliably capture individual differences. 

Methods: Firstly, the study aimed to assess the feasibility and sensitivity of detecting NAA in the hippocampus using Magnetic Resonance Spectroscopy (MRS) and a test-retest design on 11 healthy adults (seven women) spanning between the ages of 18 and 65. Secondly, the study aimed to assess the test-retest reliability of NAA measurements in the hippocampus using the ICC. Detectability thresholds were set at Signal to Noise Ratio (SNR) >3 and Full Width at Half Maximum (FWHM) <12 Hz. 

Results: Total N-acetylaspartate Tissue-Corrected Water Scaling (tNAA) was reliably detected, meeting the set SNR and FWHM criteria across all four measurements. Test-retest reliability was low (ICC = 0.26), indicating that only 26% of the total variance in the measurement was attributable to true between-participant differences. 

Discussion: The study's sample was too homogeneous, participants being too similar on the tNAA levels. The small sample can make it difficult for the measurement tool to reliably differentiate between individuals, leading to a low ICC. 

Conclusions: A low ICC indicates poor reliability and consistency in clinical measurements, meaning that repeated assessments may yield inconsistent results, making it difficult to confidently use such measures for setting a diagnosis.