diff --git a/docs/examples/tissue/plot_two_cxm.py b/docs/examples/tissue/plot_two_cxm.py
index bdf4549..8e608a3 100644
--- a/docs/examples/tissue/plot_two_cxm.py
+++ b/docs/examples/tissue/plot_two_cxm.py
@@ -24,13 +24,13 @@
 ca = osipi.aif_parker(t)
 
 # %%
-#Plot the tissue concentrations for an extracellular volume fraction
-#of 0.2, plasma volume fraction of 0.1, permeability serface area of 5 ml/min
-#and flow rate of 10 ml/min
+# Plot the tissue concentrations for an extracellular volume fraction
+# of 0.2, plasma volume fraction of 0.1, permeability serface area of 5 ml/min
+# and flow rate of 10 ml/min
 PS = 15  # Permeability surface area product in ml/min
 Fp = [10, 25]  # Flow rate in ml/min
 ve = 0.1  # Extracellular volume fraction
-vp = [0.1,0.02]  # Plasma volume fraction
+vp = [0.1, 0.02]  # Plasma volume fraction
 
 ct = osipi.two_compartment_exchange_model(t, ca, Fp=Fp[0], PS=PS, ve=ve, vp=vp[0])
 plt.plot(t, ct, "b-", label=f" Fp = {Fp[0]},PS = {PS}, ve = {ve}, vp = {vp[0]}")
diff --git a/src/osipi/_tissue.py b/src/osipi/_tissue.py
index 379e612..55af8fd 100755
--- a/src/osipi/_tissue.py
+++ b/src/osipi/_tissue.py
@@ -393,7 +393,7 @@ def two_compartment_exchange_model(
         >>> ve = 0.2  # Extracellular volume fraction
         >>> vp = 0.1  # Plasma volume fraction
         >>> ct = osipi.two_compartment_exchange_model(t, ca, Fp, PS, ve, vp)
-        >>> plt.plot(t, ca, 'r', t, ct, 'g')
+        >>> plt.plot(t, ca, "r", t, ct, "g")
 
     """
     if not np.allclose(np.diff(t), np.diff(t)[0]):
@@ -429,11 +429,20 @@ def two_compartment_exchange_model(
         vp
         * sig_p
         * sig_n
-        * ((1 - te * sig_n) * np.exp(-tau_upsample * sig_n) + (te * sig_p - 1.0) * np.exp(-tau_upsample * sig_p))
+        * (
+            (1 - te * sig_n) * np.exp(-tau_upsample * sig_n)
+            + (te * sig_p - 1.0) * np.exp(-tau_upsample * sig_p)
+        )
         / (sig_p - sig_n)
     )
 
-    irf_ce = ve * sig_p * sig_n * (np.exp(-tau_upsample * sig_n) - np.exp(-tau_upsample * sig_p)) / (sig_p - sig_n)
+    irf_ce = (
+        ve
+        * sig_p
+        * sig_n
+        * (np.exp(-tau_upsample * sig_n) - np.exp(-tau_upsample * sig_p))
+        / (sig_p - sig_n)
+    )
 
     irf_cp[[0]] /= 2
     irf_ce[[0]] /= 2
@@ -448,7 +457,7 @@ def two_compartment_exchange_model(
     t_upsample = np.linspace(t[0], t[-1], n_upsample)
 
     Cp = np.interp(t, t_upsample, Cp)
-    Ce = np.interp(t,t_upsample, Ce)
+    Ce = np.interp(t, t_upsample, Ce)
 
     # get tissue concentration
     Ct = Cp + Ce