[Modern imaging modalities in renal disease: CT and MRI]

Manual kidney stone size measurements in computed tomography are most accurate using multiplanar image reformatations and bone window settings

Computed tomography in suspected urolithiasis provides information about the presence, location and size of stones. Particularly stone size is a key parameter in treatment decision; however, data on impact of reformatation and measurement strategies is sparse. This study aimed to investigate the influence of different image reformatations, slice thicknesses and window settings on stone size measurements. Reference stone sizes of 47 kidney stones representative for clinically encountered compositions were measured manually using a digital caliper (Man-M). Afterwards stones were placed in a 3D-printed, semi-anthropomorphic phantom, and scanned using a low dose protocol (CTDIvol 2 mGy). Images were reconstructed using hybrid-iterative and model-based iterative reconstruction algorithms (HIR, MBIR) with different slice thicknesses. Two independent readers measured largest stone diameter on axial (2 mm and 5 mm) and multiplanar reformatations (based upon 0.67 mm reconstructions) using different window settings (soft-tissue and bone). Statistics were conducted using ANOVA ± correction for multiple comparisons. Overall stone size in CT was underestimated compared to Man-M (8.8 ± 2.9 vs. 7.7 ± 2.7 mm, p < 0.05), yet closely correlated (r = 0.70). Reconstruction algorithm and slice thickness did not significantly impact measurements (p > 0.05), while image reformatations and window settings did (p < 0.05). CT measurements using multiplanar reformatation with a bone window setting showed closest agreement with Man-M (8.7 ± 3.1 vs. 8.8 ± 2.9 mm, p < 0.05, r = 0.83). Manual CT-based stone size measurements are most accurate using multiplanar image reformatation with a bone window setting, while measurements on axial planes with different slice thicknesses underestimate true stone size. Therefore, this procedure is recommended when impacting treatment decision.

[New techniques in computed tomography. Significance for urology]

Computed tomographic (CT) imaging has become the modality of choice for the assessment of patients with urological malignancies. Recently, multi-slice CT imaging was introduced, providing faster acquisition times and higher resolution leading to improved image quality. Several studies show that thin-slice, high-resolution acquisition strategies lead to an improved accuracy for T-staging, especially of renal cell carcinomas. Three-dimensional post-processing techniques for the visualization of the vascular supply as well as the ureter (CT-angiography and CT-urography) are helpful for surgical planning. Compared to conventional imaging strategies unenhanced CT images render higher sensitivities and specificities for detecting stone disease in patients with acute flank pain. In the USA unenhanced CT imaging has almost replaced conventional urography, as no contrast agent is administered and the examination time is shorter. PET/CT examinations provide information on the morphology and function of tumors in one examination. However, there are only few data available for the assessment of urologic tumors.