Use of Dual Energy CT to Image Valve Settings of Programmable Shunts: Ex Vivo Testing Authors: K. Jim Hsieh, MD; Alexander C. Mamourian MD Department of Radiology University of Pennsylvania ASNR 54 th Annual Meeting and The Foundation of the ASNR Symposium May 21 st – 26 th, 2016 Washington D.C. eP-99

Disclosures The authors have no financial disclosures.

Purpose Programmable shunts are commonly used for CSF diversion because they allow modifying cerebrospinal fluid (CSF) drainage rate without the need for repeat surgery. Establishing the valve settings, however, requires a hand held device that is specific to that valve vendor or plain film x-rays oriented perpendicular to the valve. These plain films must be performed in addition to the computed tomography (CT) that is considered the standard of care in patients with suspected shunt failure.

Purpose We wondered whether dual energy CT imaging with or without metal suppression software could be used to predict shunt settings in programmable shunts since that would eliminate the need for plain films in many cases. The purpose of this scientific paper is to determine whether it is possible to use CT imaging of two common programmable shunts, i.e. Strata (Medtronic) and Hakim (Codman) ex vivo to predict the pressure settings of their programmable valves. We also investigated whether a single energy CT scanner would be sufficient since dual energy scanners are not widely available.

Photon starvation artifacts from metal is a common limitation of CT imaging. Dual energy image acquisition offers one method to reduce the magnitude of the artifact. dual energy CTvirtual high kV monoenergetic The data acquired using dual energy CT imaging (Siemens) was used here to create a virtual high energy mono energetic reconstruction (right). Photos courtesy of John Woo, M.D. University of Pennsylvania

Material and Methods A Medtronic Programmable Strata valve was applied to a dried skull and then scanned at the five settings allowed by the device. The valve changes were performed and verified using the specific hardware for that device provided by Medtronic prior to each scan. Computed tomography scans were performed on a Siemens SOMATOM Force CT scanner using dual energy with a CTDIvol of 50 mGy.

Material and Methods The source 1 mm images were used to create a set of volume rendered (VR) images using TeraRecon 3D software (Foster City, CA). These VR images were used as a reference chart of the valve appearance at each setting ( ). The skull phantom then was scanned again at the five different shunt settings in random order and this imaging data was presented as a set of unknowns to three neuroradiologists without prior knowledge of the settings for each scan and there were duplicates in the test set.

Material and Methods A Codman Hakim valve was also applied to a dried skull and scanned at three settings (50, 120, and 190) on a Siemens SOMATOM Force CT scanner with dual energy. The source 1 mm images were used to create volume rendered images using TeraRecon 3D software and evaluated using the same approach as the Strata valve.

Material and Methods We then wanted to determine if we could reproduce these results with the Medtronic Programmable Strata valve on a non-dual energy CT scanner. A Medtronic Strata Valve was again applied to a dried skull and then scanned at the five settings allowed by the device on a Siemens SOMATOM Definition Edge CT scanner using a single energy (kV 120), and source 1 mm images were used to create volume rendered images using TeraRecon 3D and analyzed.

Results The volume rendered images of the Medtronic Strata valve scanned utilizing dual energy setting with and without metal suppression had little resemblance to the appearance of the setting as seen on plain film images. For this reason the usual chart of settings was of no value. We created a “VR chart” however. We found that each of the five settings appeared differently on the volume rendered images from the others. This was validated when three neuroradiologists were able to use the table previously generated to correctly determine valve setting in each of the unknown scans.

Medtronic Strata valve chart of settings as seen on standard plain radiographs. S.S. Lollis et al. AJNR Am J Neuroradiol 2010;31: ©2010 by American Society of Neuroradiology

Reference Chart – VR images post-processed using metal suppression processing of dual energy CT data

Surface Models of Programmable Shunt Valve (Medtronic, Strata) using CT data from dual energy scanner at 1.0 and 2.5 valve settings. 1.0 valve setting 2.5 valve setting Notice the size and shape of the “shoe” (arrows). While these images do not correspond to appearance of the valve on plain films, the VR images differ at the various settings.

Programmable Shunt Valve (Medtronic, Strata), VR and plain film Notice the “bunny ears” are visible on both at this setting. 2.0 VR model from CT data Plain film image at same setting (2.0)

Reference Chart – VR images post-processed CT data using soft tissue filter (kernel) without metal suppression

Reference chart – VR images post-processed using bone filtered data and without metal suppression

Methods The imaging of the Codman device was unsuccessful since there were no unique features on the VR models that would allow us to differentiate between the different shunt settings.

Codman Hakim Programmable Valve, plain film and VR from CT. S.S. Lollis et al. AJNR Am J Neuroradiol 2010;31: ©2010 by American Society of Neuroradiology There was insufficient detail on VR image (right) to delineate the notch that shows the shunt setting that is visible on plain film image (left).

Results Since dual energy CT may not always be available at all sites we hoped to replicate the results of CT imaging of the Medtronic Strata valve on a single energy CT scanner. We found that VR image detail was not as good from this scanner as the dual energy CT scanner and for that reason proved to be insufficient to determine each of the five valve settings reliably.

Surface Models of the Strata Valve using a standard, single energy CT scanner without metal suppression. 0.5 setting 2.5 setting1.5 setting

Conclusion We demonstrated “proof of concept” ex vivo that a dual energy CT is capable of demonstrating each of the five valve settings on the Medtronic Strata programmable shunt. Further testing is necessary in vivo but if validated this capability would be beneficial since it would eliminate the need for additional imaging with plain films in cases of suspected programmable shunt malfunction. Only one of the two valves we tested offered this capability. We believe manufacturers should be aware of the benefit to patients by designing or modifying programmable valves in a fashion that would allow imaging of their settings with standard CT as well as plain films.

References Lollis SS, Mamourian AC, Vaccaro TJ, Duhaime AC. Programmable CSF Shunt Valves: Radiographic Identification and Interpretation. AJNR Am J Neuroradiol 2010;31: Mamourian AC, Pluta DJ, Eskey CJ, Merlis AL. Optimizing computed tomography to reduce artifacts from titanium aneurysm clips: an in vitro study. J Neurosurg 2007;107: