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Wednesday, August 20, 2014

3D Reconstructions of CT and MRI Data (Volume Renderings) Complimented by Medical Illustration

 By: Robert Shepherd MS, Certified Medical Illustrator, President & CEO, MediVisuals Inc.

Computer generated 3D reconstructions from a person's actual CT or MRI data (a.k.a. 3D volume renderings) as well as medical illustrations are powerful tools that can be used separately to demonstrate a plaintiff's injuries. However, when used together, they compliment each other in ways that greatly accentuate their individual effectiveness. For example, when an illustration is used along with digital 3D reconstruction, and the two images closely correspond with each other, the 3D reconstruction increases the perceived crediblility or accuracy of the illustration. The increased credibility is because of the court's perception that computer generated 3D reconstructions are free of human alteration or manipulation. Because the courts feel the images are therefore more authentic or factual than a medical illustration, the courts typically accept 3D images created from the plaintiff's actual CT or MRI data into actual evidence (as opposed to as simply demonstrative evidence).

However, when creating computer generated 3D reconstructions from the patient's authentic 3D data, human factors and involvement are still required to eliminate tissues and artifacts in order to achieve an end product. There are multiple 3D reconstruction softwares available and based on FDA (Food and Drug Administration)cleared technology. The more sophisticated the software tools, the more human involvement is required to create the end product. A technician must direct the software and make many vital decisions that will alter the appearance of the end product, such as what tissue densities will be removed to reveal underlying anatomy and pathology and what views to best appreciate those findings. When the decisions are based on sound knowledge, judgment, and experience, the images can be created in a way that helps laypeople more easily understand relevant anatomy and pathology.

The advantages of 3D reconstructions over illustrations are: 1) they are generally considered more "authentic" or accurate than illustrations because human factors are felt to be removed from the interpretation of the data; and 2) they are an affordable and fast source for a digital 3D model that allows the viewer to appreciate limited details of the anatomy or pathology from virtually any angle. The disadvantages of 3D reconstruction are: 1) the limitations of the software result in averaging of information that rounds off jagged or sharp edges of fractures and fills in small fractures that are otherwise visible in individual scan slices; and 2) the software, by itself cannot differentiate the difference between a bone joint space and fracture, therefore it cannot assign colors to differentiate between the two, unless directed by the technician. 

When color is assigned to an image created from a patient's actual CT or MRI data, the assignment of color (for example: assignment of red to an area to differentiate a fracture from a normal bone joint space) is no different than the decision an illustrator makes in assigning color to images created based upon the interpretation of CT or MRI data and images. Both methods require the human to determine what is a fracture and what is not, then to assign the color application to the area. 

The primary advantage of a medical illustrator’s creation of a 3D image of an injury (whether as a technician operating the imaging software or when creating an illustration) is that they are able to use anatomical, medical, and biomechanical knowledge to understand and further clarify the computer-generated 3D reconstructions. This deductive reasoning is similar to the deductive reasoning required by a radiologist to interpret the images: the radiologist uses similar knowledge and reasoning to create a more accurate understanding of the imaging study in their mind. A skilled medical illustrator can take this process a step further and create an actual 2D or 3D image that reduces the inaccuracies in the images generated by the software alone to result in a more, not less, accurate image. The human factor, therefore, actually results in an image that more closely resembles the plaintiff’s real injuries.

Bimalleolar Ankle Fractures:
The figure on the left is an illustration created over an AP X-ray of an ankle fracture. The figure on the right is a 3D reconstruction image from the same ankle after an external fixation device had been put in place. Note that the fractures in the 3D reconstruction are rounded off and that red artifact complicates the findings. In contrast, the illustration demonstrates the fractures with hard, sharp, or angled edges (based upon review of individual scan slices and application of deductive reasoning). Note also that some of the smaller fracture lines and fragments that only appear as bumps and lumps in the 3D reconstruction are more clearly and accurately depicted in the illustration. These fracture lines were clearly visible in the CT scan slices, but the 3D imaging software was unable to hold the detail in the 3D reconstruction.

Displaced fracture of 2nd Metatarsal:

The image on the left is an illustration of the fracture as created directly over an X-ray. The image on the right is a 3D reconstruction. Note how the 3D reconstruction rounds off the edges of the fracture, and the fracture appears very similar to one of the normal joint spaces. Note also how red artifact around the tarsal bones detracts from the actual injury. In contrast, the illustration again demonstrates the fracture with hard, sharp, angled edges. Also, as bone is known to bleed when fractured, the illustrator uses knowledge and deductive reasoning to apply red coloration to the area of the fracture and thereby represent the injury more accurately as well as further distinguishing the fracture from the various normal joint spaces.

Mandible Fractures:
Note that the edges of the fracture fragments in the 3D reconstruction are again rounded. The rounded edges and lack of color make it difficult for the untrained viewer to detect the upper left fracture. By using the 3D reconstruction as well as reviewing the individual CT slices, the medical illustrator is able to create a more accurate and understandable interpretation of the injuries. Note also that the lower teeth appear to be fused in the 3D reconstruction. This is a good example of how the imaging software's deficits do not allow it to accurately depict fine details that are evident on the individual slices. The gaps between the teeth could just as easily be small fracture lines in the bone that the 3D reconstruction failed to accurately portray, but by reviewing the individual CT scans, the illustrator can portray these details in a much more accurate representation.

Contact MediVisuals if you have any questions or would like more information on medical illustrations and/or 3D reconstructions of CT and MRI data.

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