Fix equations in PDF build

Notebooks/In Vivo Contrast Mechanisms.ipynb

@@ -66,16 +66,16 @@
     "\n",
     "The smallest size we can measure with MRI is an imaging voxel, so our image measurements are a sum of the transverse magnetizations across the voxel, including both $T_2$ and off-resonance: \n",
     "\n",
-    "$$\\begin{align}\n",
+    "$$\\begin{aligned}\n",
     "s_{\\mathrm{voxel}}(t) & = \\int_{\\mathrm{voxel}} M_{XY}(\\vec{r},0) \\exp(-t/T_2(\\vec{r})) \\exp(-i 2 \\pi \\Delta f_r(\\vec{r}))  \\  d\\vec{r} \\\\\n",
     "& \\approx M_{XY}(\\vec{r},0) \\exp(-t/T_2^*(\\vec{r}))\n",
-    "\\end{align}$$\n",
+    "\\end{aligned}$$\n",
     "\n",
     "<!-- \n",
-    "$$\\begin{align}\n",
+    "$$\\begin{aligned}\n",
     "s(t) & = \\int m(\\vec{r}) \\exp(-t/T_2(\\vec{r})) \\exp(-i 2 \\pi \\Delta f_r(\\vec{r}))  \\  d\\vec{r} \\\\\n",
     "& \\approx \\int m(\\vec{r}) \\exp(-t/T_2^*(\\vec{r})) \\ d\\vec{r}\n",
-    "\\end{align}$$\n",
+    "\\end{aligned}$$\n",
     "-->\n",
     "\n",
     "(Note that any effects of applied gradients are removed during the image reconstruction process.)\n",

Notebooks/K-space.ipynb

@@ -48,10 +48,10 @@
     "\n",
     "The MRI signal comes from the precession of the transverse magnetization, and thus is proportional to the transverse magnetization.  The MRI signal also comes from any precessing magnetization within the sensitive volume of the RF receive coils.  In other words, it is also not localized to a single location, but rather is summed over a volume:\n",
     "\n",
-    "$$\\begin{align}\n",
+    "$$\\begin{aligned}\n",
     "s(t) & = \\int M_{XY}(\\vec{r},t) \\ d\\vec{r} \\\\\n",
     " & =  \\int m(\\vec{r}) \\exp(-i2\\pi \\vec{k}(t) \\cdot \\vec{r}) \\ d\\vec{r}\n",
-    " \\end{align}$$ \n",
+    " \\end{aligned}$$ \n",
     "\n",
     "The amazing result here is that this describes our MRI signal in the form of a Fourier Transform:\n",
     "\n",