diff --git a/tedana/utils.py b/tedana/utils.py
index 6b88f1da0..356e27b99 100644
--- a/tedana/utils.py
+++ b/tedana/utils.py
@@ -104,16 +104,21 @@ def make_adaptive_mask(data, mask, threshold=1):
             -   This is the threshold for "good" data.
             -   The 1/3 value is arbitrary.
             -   If there was more than one exemplar voxel,
-                retain the the highest value across the exemplars for each echo.
-        d.  For each voxel, count the number of echoes that have a mean value greater than the
+                retain the echo-wise values from the exemplar with the highest total value.
+        d.  For each voxel, identify the last echo with a mean value greater than the
             corresponding echo's threshold.
+
+            -   Preceding echoes (including ones with mean values less than the threshold)
+                are considered "good" data.
     """
     RepLGR.info(
         "An adaptive mask was then generated, "
         "in which each voxel's value reflects the number of echoes with 'good' data."
     )
-    mask = reshape_niimg(mask).astype(bool)
-    data = data[mask, :, :]
+    # mask = reshape_niimg(mask).astype(bool)
+    # data = data[mask, :, :]
+
+    n_samples, n_echoes, _ = data.shape
 
     # take temporal mean of echos and extract non-zero values in first echo
     echo_means = data.mean(axis=-1)  # temporal mean of echos
@@ -121,40 +126,46 @@ def make_adaptive_mask(data, mask, threshold=1):
 
     # get 33rd %ile of `first_echo` and find corresponding index
     # NOTE: percentile is arbitrary
-    # TODO: "interpolation" param changed to "method" in numpy 1.22.0
-    #       confirm method="higher" is the same as interpolation="higher"
-    #       Current minimum version for numpy in tedana is 1.16 where
-    #       there is no "method" parameter. Either wait until we bump
-    #       our minimum numpy version to 1.22 or add a version check
-    #       or try/catch statement.
-    perc = np.percentile(first_echo, 33, interpolation="higher")
-    perc_val = echo_means[:, 0] == perc
+    perc = np.percentile(first_echo, 33, method="higher")
+    voxels_at_perc = echo_means[:, 0] == perc
 
     # extract values from all echos at relevant index
     # NOTE: threshold of 1/3 voxel value is arbitrary
-    lthrs = np.squeeze(echo_means[perc_val].T) / 3
+    lthrs = np.squeeze(echo_means[voxels_at_perc, :].T) / 3
 
-    # if multiple samples were extracted per echo, keep the one w/the highest signal
+    # if multiple voxels exactly match the 33rd percentile value in the first echo,
+    # retain the values from the voxel with the highest total value across echoes
     if lthrs.ndim > 1:
         lthrs = lthrs[:, lthrs.sum(axis=0).argmax()]
 
-    # determine samples where absolute value is greater than echo-specific thresholds
-    # and count # of echos that pass criterion
-    masksum = (np.abs(echo_means) > lthrs).sum(axis=-1)
+    # Find the last good echo for each voxel
+    # Add a 1 to the end of the threshold array to match the size of the echo_means array
+    lthrs = np.hstack((lthrs, 1))
+    # Add a 0 to the end of the echo_means array to make a trailing echo "bad".
+    # This way, argmax can distinguish between all bad echoes and having the last echo be good.
+    # The former will have a value of n_echoes + 1, while the latter will have a value of n_echoes.
+    echo_means = np.hstack((echo_means, np.zeros((n_samples, 1))))
+    # argmax finds the first instance of the maximum value, so we need to reverse the order
+    # of the array to find the last instance of the maximum value.
+    masksum_inverted = np.argmax(np.abs(echo_means[:, ::-1]) > lthrs[::-1], axis=1)
+    masksum = n_echoes - masksum_inverted
+    # Replace values of n_echoes + 1 (all bad echoes) with 0 (no good echoes)
+    masksum[masksum == n_echoes + 1] = 0
 
     # TODO: Use visual report to make checking the reduced mask easier
     if np.any(masksum < threshold):
         n_bad_voxels = np.sum(masksum < threshold)
         LGR.warning(
-            f"{n_bad_voxels} voxels in user-defined mask do not have good "
-            "signal. Removing voxels from mask."
+            f"{n_bad_voxels} voxels in user-defined mask do not have good signal. "
+            "Removing voxels from mask."
         )
         masksum[masksum < threshold] = 0
 
+    masksum = masksum * mask.astype(bool)
     modified_mask = masksum.astype(bool)
 
-    masksum = unmask(masksum, mask)
-    modified_mask = unmask(modified_mask, mask)
+    # masksum = unmask(masksum, mask)
+    # modified_mask = unmask(modified_mask, mask)
 
     return modified_mask, masksum