diff --git a/.github/actions/conda/action.yaml b/.github/actions/conda/action.yaml
index b7240e6..266cbad 100755
--- a/.github/actions/conda/action.yaml
+++ b/.github/actions/conda/action.yaml
@@ -21,7 +21,7 @@ inputs:
     description: 'Override'
     required: false
     default: true
-  password: 
+  password:
     required: true
 runs:
   using: "composite"
@@ -40,7 +40,8 @@ runs:
   - uses: conda-incubator/setup-miniconda@v2
     with:
       mamba-version: "*"
-      channels: balbasty,pytorch,conda-forge,defaults
+      miniforge-version: latest
+      channels: balbasty,pytorch,conda-forge
       channel-priority: true
       activate-environment: build
   - name: Install boa / anaconda
@@ -73,7 +74,7 @@ runs:
   - name: "Publish (dry run: ${{ inputs.dry-run }})"
     if: inputs.dry-run == 'false'
     shell: bash -el {0}
-    env: 
+    env:
       OVERRIDE: ${{ inputs.override }}
       PLATFORMS: ${{ inputs.platforms }}
       ANACONDA_API_TOKEN: ${{ inputs.password }}
diff --git a/.github/actions/test/action.yaml b/.github/actions/test/action.yaml
index be7af89..c2f9b78 100755
--- a/.github/actions/test/action.yaml
+++ b/.github/actions/test/action.yaml
@@ -22,12 +22,13 @@ runs:
     - uses: conda-incubator/setup-miniconda@v2
       with:
         mamba-version: "*"
+        miniforge-version: latest
         python-version: ${{ inputs.python-version }}
-        channels: balbasty,pytorch,conda-forge,defaults
+        channels: balbasty,pytorch,conda-forge
         activate-environment: test-env
     - name: Install dependencies
       shell: bash -el {0}
-      env: 
+      env:
         PYTORCH_VERSION: ${{ inputs.pytorch-version }}
       run: |
         mamba install pytorch=${PYTORCH_VERSION} pytest
@@ -35,4 +36,4 @@ runs:
       shell: bash -el {0}
       run: |
         pip install .
-        pytest --pyargs cornucopia
\ No newline at end of file
+        pytest --pyargs cornucopia
diff --git a/cornucopia/intensity.py b/cornucopia/intensity.py
index c3a620b..2b23dfb 100755
--- a/cornucopia/intensity.py
+++ b/cornucopia/intensity.py
@@ -30,6 +30,7 @@
 from .random import Sampler, Uniform, RandInt, Fixed, make_range
 from .utils.py import ensure_list, positive_index
 from .utils.smart_inplace import add_, mul_, div_, pow_
+from .utils.compat import clamp
 
 
 class OpConstTransform(FinalTransform):
@@ -175,7 +176,7 @@ def xform(self, x):
             vmin = vmin.to(x)
         if torch.is_tensor(vmax):
             vmax = vmax.to(x)
-        y = x.clamp(vmin, vmax)
+        y = clamp(x, vmin, vmax)
         return prepare_output(
             {'input': x, 'output': y, 'vmin': vmin, 'vmax': vmax},
             self.returns
diff --git a/cornucopia/qmri.py b/cornucopia/qmri.py
index f3df192..0108430 100755
--- a/cornucopia/qmri.py
+++ b/cornucopia/qmri.py
@@ -425,34 +425,28 @@ def __init__(self, tr=25e-3, te=7e-3, alpha=20,
         self.mt = mt
 
     def get_parameters(self, x):
-        x = x.unbind(0)
         if self.pd is None:
-            pd, *x = x
-            pd = pd[None]
+            pd, x = x[:1], x[1:]
         else:
             pd = self.pd
         if self.t1 is None:
-            t1, *x = x
-            t1 = t1[None]
+            t1, x = x[:1], x[1:]
         else:
             t1 = self.t1
         if self.t2 is None:
-            t2, *x = x
-            t2 = t2[None]
+            t2, x = x[:1], x[1:]
         else:
             t2 = self.t2
-        if self.b1 is None:
-            b1, *x = x
-            b1 = b1[None]
-        else:
-            b1 = self.b1
         if self.mt is None:
-            mt, *x = x
-            mt = mt[None]
+            mt, x = x[:1], x[1:]
         else:
             mt = self.mt
+        if self.b1 is None:
+            b1 = x
+        else:
+            b1 = self.b1
 
-        return pd, t1, t2, b1, mt
+        return pd, t1, t2, mt, b1
 
     def xform(self, x):
         """
@@ -468,7 +462,7 @@ def xform(self, x):
                 - b1: Transmit efficiency (B1+). `1` means 100% efficiency.
                 - mt: Magnetization transfer saturation (MTsat).
         """
-        pd, t1, t2, b1, mt = self.get_parameters(x)
+        pd, t1, t2, mt, b1 = self.get_parameters(x)
         alpha = (math.pi * self.alpha / 180) * b1
         if torch.is_tensor(alpha):
             sinalpha, cosalpha = alpha.sin(), alpha.cos()
@@ -597,8 +591,11 @@ def sigmoid_(x):
         logmt = logit(mt)
         logsigma = sigma.log()
 
+        nb1 = len(b1) if (torch.is_tensor(b1) and b1.ndim > 0) else 1
+
         dtype = x.dtype if x.is_floating_point() else torch.get_default_dtype()
-        y = x.new_zeros([5, *x.shape[1:]], dtype=dtype)
+        y = x.new_zeros([4 + nb1, *x.shape[1:]], dtype=dtype)
+        print(y.shape)
         # PD
         y[0] = exp_(GaussianMixtureTransform(
             mu=logpd, sigma=logsigma[:n], fwhm=fwhm[:n],
@@ -614,13 +611,13 @@ def sigmoid_(x):
             mu=logt2, sigma=logsigma[2*n:3*n], fwhm=fwhm[2*n:3*n],
             background=0, dtype=dtype
         )(x)).squeeze(0)
-        # B1
-        y[4:] = b1
         # MT
         y[3] = sigmoid_(GaussianMixtureTransform(
             mu=logmt, sigma=logsigma[3*n:4*n], fwhm=fwhm[3*n:4*n],
             background=0, dtype=dtype
         )(x)).squeeze(0)
+        # B1
+        y[4:].copy_(b1)  # NOTE: y[4:] = b1 breaks the graph in torch 1.11
 
         # GRE forward mode
         mask = (1 - x[0]) if x.dtype.is_floating_point else (x != 0)
diff --git a/cornucopia/utils/compat.py b/cornucopia/utils/compat.py
new file mode 100644
index 0000000..8b604f5
--- /dev/null
+++ b/cornucopia/utils/compat.py
@@ -0,0 +1,30 @@
+from typing import Optional
+import torch
+
+Tensor = torch.Tensor
+
+
+torch_version = torch.__version__
+torch_version = torch_version.split("+")[0]     # remove local modifier
+torch_version = torch_version.split(".")[:2]    # major + minor
+torch_version = tuple(map(int, torch_version))  # integer
+
+
+if torch_version < (1, 9):
+    def clamp(
+        x: Tensor,
+        min: Optional[Tensor] = None,
+        max: Optional[Tensor] = None,
+        **kwargs
+    ):
+        if torch.is_tensor(min):
+            x = torch.maximum(x, min, **kwargs)
+            min = None
+        if torch.is_tensor(max):
+            x = torch.minimum(x, max, **kwargs)
+            max = None
+        if min is not None or max is not None:
+            x = x.clamp(min, max, **kwargs)
+        return x
+else:
+    clamp = torch.clamp