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Dual Energy – Evaluation of Kidney Stones

SOMATOM Definition abdominal scan with spiral dual energy

Author: Anno Graser, M.D., Thorsten Johnson, M. D., and Christoph R. Becker, M. D.
Department of Clinical Radiology, University of Munich - Grosshadern Campus

History

A 34 year-old male (A) and a 55 year-old male (B) patient were both referred for MDCT evaluation of a known urolithiasis. A non-enhanced MDCT scan of the abdomen was performed on the SOMATOM Definition using spiral Dual Energy evaluation.

 

Diagnosis
The Dual Energy acquisition allowed not only a precise localization of the kidney stones in both patients, moreover it permitted a characterization of the scanned tissue, or material.. The red color-code of the kidney stone shown in Patient A indicates a uric acid stone. After the Dual Energy CT, we could transfer the patient for drug therapy treatment. Subsequently, the stone passed spontaneously, and was analyzed. The analysis confirmed that the concrement consisted of 100% uric acid. The blue color-code shown in Patient B characterizes a calcium oxalate stone. Based on this Dual Energy study, the stone was removed in an interventional procedure. The lab analysis of the removed stone confirmed the calcium oxalate composition.

 

Comments
The majority of kidney stones can be grouped as either calcium oxalate stones (65%) or uric acid material (15%). Conventional CT imaging helps to locate and visualize the kidney stone. However, a fast and secure characterization is not possible. Dual Energy scanning overcomes this limitation and enables us to differentiate the scanned tissue. The SOMATOM Definition permits the use of two sources at two different kV levels simultaneously. The result are two spiral data sets acquired in a single scan providing diverse information, which allows to differentiate, characterize, isolate, and distinguish the imaged tissue and material as shown in Figure 1b and 2b. A corresponding treatment decision can be immediately taken, avoiding unnecessary hospitalization of the patient.
 

Using conventional CT imaging the kidney stones (arrows) can clearly be visualized; however its composition can not be characterized.
Fig. 2a: The Dual Energy scan enables the characterization of tissue and other materials. In patient A the kidney stone could be identified as uric acid stone, color-coded in red.
Fig. 2b: Spiral Dual Energy enables the characterization of the kidney stone in Patient B as calcium oxalate stone, color-coded in blue (same color as cortical bone).

Examination Protocol

Scanner SOMATOM Definition SOMATOM Definition
Patient Patient A Patient B
Scan area Abdominal Scan Abdominal Scan
Scan length 377 mm 215 mm
Scan direction Craniocaudal Craniocaudal
kV 140 kV and 80 kV 140 kV and 80 kV
Effective mAs 64 eff. mAs and 352 eff. mAs 69 eff. mAs and 351 eff. mAs
Rotation time 0.5 sec 0.5 sec
Slice collimation 0.6 mm 0.6 mm
Spatial resolution 0.33 mm 0.33 mm
Slice width 1 mm 1 mm
Reconstructed slice thickness 0,75 mm 0,75 mm
Increment 0,5 mm 0,5 mm
Kernel B30f B30f
Bolus tracking Off Off
Care Dose 4D On On

Date: 2007-04-24


Case Studies

The information presented 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 Healthcare 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 system. The source for the technical data is the corresponding data sheets. Results may vary.

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