  In this paper, we view matrix frames as representations of quivers and study
them within the general framework of quiver invariant theory. We are thus led
to consider the large class of semi-stable matrix frames. Within this class, we
are particularly interested in radial isotropic and Parseval matrix frames.
  Using methods from quiver invariant theory [CD19], we first prove a far
reaching generalization of Barthe's Radial Isotropy Theorem [Bar98] to matrix
frames (see Theorems 1(3) and 28). With this tool at our disposal, we provide a
quiver invariant theoretic approach to Paulsen's problem for matrix frames. We
show in Theorem 2 that for any given $\varepsilon$-nearly equal-norm Parseval
frame $\mathcal{F}$ of $n$ matrices with $d$ rows there exists an equal-norm
Parseval frame $\mathcal{W}$ of $n$ matrices with $d$ rows such that
$\mathsf{dist}^2(\mathcal{F},\mathcal{W})\leq 26 \epsilon d^2$.
