To evaluate the feasibility of ultrasound (US) computed tomography (CT) or magnetic resonance imaging (MRI) fusion imaging (FI) for localization and assessment of kidney lesions.
Twenty-eight consecutive patients undergoing FI at our department were retrospectively analyzed in this study. All patients underwent solitary gray-scale US as well as FI with US/CT or US/MRI. If a kidney lesion was described as indeterminate in the previous CT or MRI, FI was additionally combined with CEUS. Exclusion criteria were age <18 years, unstable coronary heart disease and cardiac pacemaker.
A kidney lesion with >20 HU in an unenhanced CT scan was defined as a lesion with high attenuation. Kidney lesions that showed an increased attenuation in a range of 10-20 HU after application of contrast agent were defined as borderline CE lesions . Data were handled according to the World Medical Association Declaration of Helsinki (59th WMA Assembly, Seoul, 2008). Institutional Review Board approval was further granted utilizing a general waiver for studies with retrospective data analysis (Ethikkommission, Med. Univ. Innsbruck; 2009-02-20).
Indications for fusion imaging
In 16 out of 28 patients (57.1%), FI was performed because it was not possible to precisely localize the lesion of interest due to multiple and directly adjacent similar injuries within one kidney. In 12 out of 28 patients (42.9%), the kidney lesions were solitary or at least isolated but indefinable by the gray-scale US alone due to small lesion size, isoechogenicity and a sonographically difficult anatomical location near the upper apical pole.
Feasibility of fusion imaging
FI was performed successfully in 25 out of 28 (89.3%) patients. In three out of 28 (10.7%) patients, FI failed, and lesions were not confidently detected due to general US limitations, namely insufficient patient compliance with small lesion size in one patient (6 mm) and obesity in two patients.
In the present study, we showed that FI of US with CT/MRI is a feasible technique for localizing challenging kidney lesions. FI was performed successfully in the majority (89.3%) of patients in which either a kidney lesion of interest could not definitively be localized due to multiple and directly adjacent similar lesions or an indeterminate kidney lesion was solitary but could not be sufficiently defined with the gray-scale US alone.
In the remaining 10.7% of the patients, the detection of a kidney lesion by FI failed due to general US limitations such as insufficient patient compliance or patient obesity. FI of US and previously acquired CT or MRI datasets is a possible imaging technique for detecting kidney lesions which are hard to define by gray-scale US alone. FI with CEUS can be utilized especially when the differentiation of a solid hypovascular lesion from a cystic lesion remains unresolved after CT/MRI imaging, or contrast-enhanced CT/MRI is contraindicated.