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Dual Energy CT: Virtual Non-Contrast Imaging of a Complicated Renal Cyst.

SOMATOM Definition Flash Scanning

Author: By Shuichi Kawada MD*, Yutaka Imai MD PhD*, Sayoko Miyanishi**
*Department of Radiology, Tokai University, Kanagawa, Japan
** Siemens Japan K.K., Imaging & Therapy Systems Div., Tokyo, Japan

History

A 40-year-old female came to the emergency department with lower abdominal pain. Her anamnesis included systemic lupus erythematosus with chronic renal impairment caused by lupus nephritis. She had been on hemodialysis for about 10 years after going through peritoneal dialysis. A Dual Energy CT scan for detailed examination was ordered. From the Dual Energy CT data, we generated an iodine map and a virtual non-enhanced (VNC) image for comparison with a true non-enhanced CT that we had taken one month earlier.


Diagnosis
The CT images revealed kidney atrophy on both sides and multiple cystic lesions. Inside the left upper kidney, a uniform region with slightly higher density than the surrounding tissue was seen. We suspected a complicated cyst, but could not distinguish on the contrast enhanced CT images whether the region showed higher density due to contrast medium uptake. The iodine map and the fused iodine and VNC images showed that the high density region did not contain contrast medium. From the comparison of VNC and true non-enhanced CT images, we could confirm that the lesion was a complicated cyst of homogeneously high attenuation corresponding to a category II cystic lesion according to Bosniak Criteria. No treatment was required. The patient remained in the hospital for observation and could be released three days later.
 

Comments
According to Bosniak Criteria complicated category II cysts show homogeneously high attenuation without iodine uptake. They are therefore difficult to distinguish from iodine enhancing lesions on contrast enhanced CT. Dual Energy CT was found very useful for this case. Virtual non-contrast images and iodine maps can be extracted out of a single acquisition. In addition, the Selective Photon Shield introduced with the SOMATOM Definition Flash proved useful in further separation of the two tube’s X-ray spectra during acquisition. It leads to an improved material decomposition. Furthermore, the patient did not receive additional dose from the Dual Energy CT scan compared to a conventional single energy CT scan.
 

Fused 100 kV and 140 kV images give a mixed image that corresponds to a 120 kV single energy image. A high density region can be seen in the left kidney (arrow).
With fused iodine and VNC images of a 50/50 ratio the high density region inside the left kidney does not to contain iodine (arrow).
The pure Iodine image shows a region of no iodine uptake (arrow).
A true non-contrast image was taken one month previously.
Even the virtual non-enhanced image showed that the lesion did not contain contrast medium.
Fused iodine and VRT image.
Coronal fused iodine and VNC images of a 50/50 ratio visualized the hypodense region well (arrow)..
The same could be shown in the coronal iodine image (arrow).
The same could be shown in the coronal VNC image (arrow).

Examination Protocol

ScannerSOMATOM Definition Flash
Scan modeDual Energy VNC
Scan areaAbdomen Pelvis
Scan length435 mm
Scan directionCranio-Caudal
Scan time19 s
Tube voltage100 kV / 140 kV
Tube current140 mAs / 119 mAs
Dose modulationCARE Dose4D
CTDIvol11.57 mGy
DLP523 mGy*cm
Rotation time0.5 s
Slice collimation32 x 0.6
Slice width1.5 mm
Reconstruction Increment1.5 mm
Reconstruction kernelD30f
Contrast
Volume100 ml (300 mgI/ml)
Flow Rate1.5 ml/s
Start delay120 s

The information presented in this case study is for illustration only and is not intended to be relied upon by the reader for instruction as to the practice of medicine. Any health care practitioner reading this information is reminded that they must use their own learning, training and expertise in dealing with their individual patients. This material does not substitute for that duty and is not intended by Siemens Medical Systems to be used for any purpose in that regard.

The drugs and doses mentioned herein are consistent with the approval labelling for uses and/or indications of the drug. The treating physician bears the sole responsibility for the diagnosis and treatment of patients, including drugs and doses prescribed in connection with such use. The Operating Instructions must always be strictly followed when operating the CT System. The source for the technical data is the corresponding data sheets. Results may vary.

Effective Dose was calculated using the published conversion factor for a adult abdomen & pelvis of 0.015 mSv mGyˉ1cmˉ1 [1]. [1] McCollough CH et al. Strategies for Reducing Radiation Dose in CT, Radiol Clin N Am 47 (2009) 27–40

Date: Apr 13, 2011


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