\section* {Introduction}
MRI provides a non-invasive  way to detect   long-range intermolecular multiple-quantum coherence (iMQC) via dedicated multiple spin echo (MSE) sequences  \cite{225062:5039968,225062:5040922,225062:5067325}.
In the quantum mechanical formalism by Warren \unskip~\cite{225062:5067241,225062:5042514},  all dipolar-couplings are taken into account explicitly but only those contributions dominate which  retain the  classical formalism that was initially introduced to describe MSE \cite{Jeener_2000}. MSEs are highly sensitive to spherical  symmetries \unskip~\cite{225062:5067412,225062:5041128,225062:5067413,225062:5067414} and dipole angulation. 
 Despite the dipole field angulation, MSEs have always a similar signal contrast in single-quantum coherence (SQC), mainly because  short-range iMQC influences also SQC  via T$_1$ and T$_2$ relaxation. Otherwise, specialized sequences are available like  diffusion MRI sequences which are able to detect  broken spherical symmetry (restricted diffusion).
For the measurement of long-range dipole-dipole interactions,  asymmetric magnetic field gradients ( asymmetric integrated over time) are applied in combination with at least two radio-frequency (RF) pulses \cite{225062:5039968,225062:5040922,225062:5067325}. This situation is similar to fast repeated single-slice gradient-echo echo planar imaging (GE-EPI) series, where  so-called  crusher gradients (to dephase any SQC signal that remains from the previous excitation) are added between two acquisitions (see figure \ref{548938}).
Therefore,  every second image could contain SQC and iZQC components whereby  the ratio of the iZQC to SQC  only reaches up to 0.02 at 4 T  \cite{Warren_1998,Rizi_2000} which fits the theoretical expectation well. At 3 T and without an optimized sequence this ratio should be substantively lower, which means that the iZQC signal is negligible in fast imaging series due to low signal-to-noise provided that there are no exotic quantum effects.
In our experiments, we used a conventional GE-EPI series with a short repetition time (TR) and two additional saturation pulses. The saturation pulses were introduce to increase long-range correlation via the additional gradients by a factor of around 6. 
\section*{Results}
 With this sequence, we found predominate alternations with the cardiac frequency in brain tissue.  In each cardiac cycle, we observed a period which varied in length between 150 and 420 ms showing an alternating signal of up to 15 \%  as plotted in Figure~\ref{125409} and \ref{499388}A  to which we will refer in the following as zigzags. 
