Interactive MRS Data Analysis

Analysis Pipeline

Adjust parameters to see their effect on the Free Induction Decay (FID) and the resulting Spectrum.

Noise Level 0.5

Simulates thermal noise from the coil.

Add Broad Baseline

What is this?

Simulates signals from macro-molecules or lipids that decay very fast in the time domain (short T2*) and thus appear as very wide, rolling "humps" under the sharp metabolite peaks in the frequency spectrum.

Dominant Water Peak

Apply Water Suppression Filter

Why do we need this?

Because water concentration in tissue is roughly 10,000 times higher than metabolites. Without suppressing or mathematically filtering the massive water peak, the tiny signals from NAA or Choline are completely dwarfed and cannot be analyzed properly. This filter subtracts a modeled water peak from the FID.

Line Broadening (Hz) 2.0

Why Apodization?

Apodization (multiplying the FID by a decaying exponential e^-t·π·LB) artificially increases T2* decay. This heavily suppresses the noisy tail of the FID, improving Signal-to-Noise Ratio (SNR) in the spectrum, but at the cost of making the spectral peaks lower and broader (decreasing spectral resolution).

Zero-Filling (Interpolation)

What does padding zeros do?

Zero-Filling entails padding the end of the time-domain FID with zeros. When we apply the FFT (Fast Fourier Transform) to this longer array, it effectively interpolates the data points in the frequency domain. It doesn't add new information to the spectrum or improve true resolution, but it makes the peaks look curvier and easier to fit.

Zero-Order Phase (φ₀) 0°

First-Order Phase (φ₁) 0°

Why Phase Correction?

Due to hardware delays (acoustic delay) or starting phase offsets, the raw FFT outputs a mix of absorptive (positive hill) and dispersive (S-curve) lineshapes. We desire purely absorptive peaks to accurately calculate the area under the curve (Metabolite Concentration).

(φ₀) rotates phase uniformly across all frequencies.
(φ₁) rotates phase linearly with frequency to fix frequency-dependent delays.

Time Domain: Free Induction Decay (Real Part)

Frequency Domain: MRS Spectrum (Real Part)