# Hands-On Deformation of Volumetric Anatomical Images on a Touchscreen
## 8 Discussion  
Our work is best classified as an enabling technology that opens the door to new possibilities. The two major areas of potential application are exploration for diagnosis and pre-operative planning. Next, we discuss in more detail how the features of our method could be leveraged in some specific applications.  
Our direct interaction methods provide the ability to easily move and rotate anatomical elements, thus uncovering back surfaces or enabling access to hidden areas. This is particularly useful if the region of interest is on the backside of an anatomical element, or hidden behind layers of anatomy. The traditional approach is to navigate the view and adapt the volume rendering settings to display the region of interest, but in some cases the clinician may want to retain a certain overall view and/or combine viewing of the region of interest with motion of the anatomy.  
One example is exploration through motion, deformation and palpation of the anatomy. Provided that the mechanical behavior is accurate enough, the clinician may virtually palpate the anatomy and identify clinically relevant features. palpation can aid in the detection and understanding of, e.g., cancerous tissue [55].  
Another example is planning of interventions when the anatomy is hidden from the point of entry of the surgical tools. Some of the decisions that could be planned include the point of entry itself, directions for cutting, or the amount of admissible motion and deformation of organs under safety conditions. For the specific case of the abdominal anatomy shown in our examples, particular clinical cases that could leverage our tools include resection of retroperitoneal tumors with complicated accessibility, e.g., partial  
Figure 8: Video images of the user performing natural hands-on deformation of volumetric anatomy, interacting with the actual touchscreen. **Top row**: in-plane translation and rotation of the kidney using two fingers. **Bottom row**: out-of-plane rotation of the kidney using three fingers. The arrows show the direction of motion.  
nephrectomy [56], tumor resection in the adrenal gland hidden by the pancreas [57], or liver surgery in back/hidden areas of the liver.  
With our proposed interaction metaphor, the clinician may simply move organs around, separate them, and rotate them to inspect various views, all through a simple \"grab and move\" action, much like we manipulate objects in the real world. In open surgery, the region of interest may be behind other anatomy layers. It is not enough to just \"erase\" these layers in the view of the volume image, as in reality they are cut and moved, and when moved they pull from other anatomy, possibly also at the region of interest. Our prototype implementation of tangible interaction is a first step toward mimicking these operations in an effective manner. Note that, for planning, it is not necessary to move the anatomy using realistic tools; it is sufficient to \"grab\" the anatomy and move it, with the connected tissue following in a physically accurate manner. The extent of the handle selection (Section 4) defines the part of an organ that is \"grabbed\". Once the clinician moves a handle, it may be kept in place to keep clear access to the region of interest. The clinician could rotate an organ and visualize and explore blood vessels in the region of interest. The amount of admissible rotation depends on patient-specific mechanical response and requires a physics-based deformation model. Then, this rotation could be planned without compromising the safety of blood vessels due to excessive tension.