Despite of the diagnostic potential of conventional CT (CCT), limitations being inherent in this technology reduce its diagnostic confidence and limit clinical CT applications as 3D imaging. Helical CT (HCT) has far overcome the limitations of CCT and has become the standard CT technology. After a short overview on the technique of HCT and its advantages over CCT, the impact of HCT on the detection of disorders of the urinary organs is discussed. Due to the high quality of 3D reconstructions, vessels are visualized free of artefacts resulting in a dramatic improvement and acceptance of CT angiography, which has become a clinically important examination in the evaluation of obstructive renal artery disease. Fast HCT provides a precise assessment of the three phases of the nephrogram and it is a prerequisite for an improved depiction of abnormal vascular perfusion and impaired tubule transit of contrast material. Helical CT enables an improved characterization of cystic mass lesions reducing the diagnosis of indeterminate masses and thus facilitating a better therapeutic management. The diagnosis of renal cell carcinomas (RCC) has improved due to an increased sensitivity in detecting small RCCs, and an increased specificity in the diagnosis of neoplastic lesions. Improved staging of RCCs is the result of accurate assessment of venous tumour extension. When planning nephron-sparing surgery 3D display of the renal tumour helps to determine the resectability of the mass depicting its relation to major renal vessels and the renal collecting system. In the evaluation of renal trauma HCT provides shorter scanning time and thus fewer artefacts in the examination of traumatized patients who cannot cooperate adequately. Three-dimensional postprocessing modalities allow the assessment of the renal vascular pedicel by CT angiography and improve the demonstration of complex lacerations of the renal parenchyma. In the evaluation of the upper urinary tract unenhanced HCT has become the imaging method of choice in the diagnosis and differential diagnosis of acute flank pain since it is highly sensitive and specific in detecting calculus disease. Unenhanced HCT may furthermore demonstrate causes of flank pain unrelated to urolithiasis. Gapless volume scanning and improved resolution in the z-axis during the excretory phase enables improved visualization of the renal collecting systems and ureters, resulting in a better demonstration of intraluminal and extraluminal pathology.
IntroductionImaging algorithms of the liver have undergone continuous change over the last 15 years. While liver sonography was a first-choice modality in the past, computed tomography (CT) has become the leading modality in most institutions because of multiphasic and dynamic imaging capabilities. With the introduction of new breath-hold sequences and specific contrast agents during the last decade, the role of magnetic resonance (MR) imaging has changed from a pure problem-solver in lesion characterization to a first-step modality in hepatic imaging. Recent advances in functional imaging have introduced contrast-enhanced sonography and 18-FDG-PET as innovative and promising techniques into the broad spectrum of liver imaging. Imaging methods SonographySince sonography is easily available, noninvasive, and provides a depth-dependent spatial resolution combined with a good signal-to-noise ratio in most pathologic entities of the liver, it plays an important role in the firststep imaging evaluation providing high detection and specificity rates in capable hands. However, because sonography is highly operator-and equipment-dependent, sensitivity and specificity values vary significantly from institution to institution and are generally inferior to those of dynamic helical (multidetector) CT and MR imaging.The sensitivity of conventional "gray-scale" sonography in the detection of liver metastases, as reported in the literature, is highly dependent on the study design and the referred "gold standard" and ranges between 53% and 77% [1, 2]. Thus, sonography commonly yields lover detection rates than contrast-enhanced CT or MR imaging, which may be caused either by iso-echogenic focal lesions with a poor lesion-to-liver contrast, diminished spatial resolution with increasing insonation depth, poor acoustic properties in obese patients, or generally by a disadvantageous anatomical location.With the development of first-generation microbubble suspensions containing air, which act as acoustic backscatter, dynamic imaging of the liver was introduced into sonography. Second-generation agents, such as SonoVue (Bracco Imaging, Milan, Italy), taking advantage of stable phospholipid-coated gas particles, can withstand much better the acoustic pressure of insonation resulting in an increased half-time of the agent and thus providing a prolonged diagnostic window. These agents are used not only to increase the Doppler signal amplitude during the vascular phase, but also to differentiate hepatocellular tissue from neoplastic disease. The selective uptake of these microbubbles by ultrastructurally normal liver parenchyma with a probable interaction with the reticuloendothelial system (RES) during the "late phase", i.e. 2-4 min after contrast administration, will increase the lesion-to-liver contrast. Since nonhepatocellular tissue, e.g. metastases, is not able to "store" the microbubbles, it appears as hypoechoic "hole" in contrast-enhanced sonography (Fig. 1). This fact has led to the ongoing routine use of secondgeneration ultras...
This study showed the capability of triplex Doppler ultrasound signal enhancement after Optison. 1.0 mL Optison proved to be the more appropriate dose for an optimal signal enhancement than 0.3 mL Optison.
Because of the anatomic localisation of the retroperitoneal space, the detection and elucidation of pathology in the retroperitoneum calls for clinical acumen and the utilisation of imaging techniques. During the past two decades, efforts spearheaded by the work of M. A. Meyers led to an enhanced understanding of retroperitoneal anatomy and pathology. Conventional radiographic techniques are often incapable of detecting and/or characterising retroperitoneal abnormalities. Sonography may be limited by patient-dependent-factors. CT is unaffected by bowel gas and provides discrete cross-sectional images of the organs, fascial planes and retroperitoneal compartments, making it an ideal tool for assessment of retroperitoneal disease. In clinically stable patients MRT may be a useful modality for providing helpful and additional information in characterising retroperitoneal abnormalities. In this review article the diagnostic possibilities of benign not organ-related diseases of the retroperitoneum are described. This is intended to give the reader an insight into the etiology and distribution patterns of retroperitoneal fluid and gas collections as well as into diagnosis and differential diagnosis of benign retroperitoneal diseases. The diagnostic impact of the different imaging modalities is discussed.
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