Multidetektorcomputertomographie (MDCT) der Nieren

Multidetector computed tomography (MDCT) possesses distinct advantages for examination of the kidneys. It carries the potential of becoming the gold standard of diagnostic work-up and surgical planning for most renal diseases and replacing conventional methods such as i.v. urography and angiography. The most outstanding improvements, in comparison to single slice spiral CT, are the speedier image acquisition and enhanced z-axis resolution, which aids particularly in visualization of the urinary tract as it aligns along the axis of the body. Respiratory artifacts are few or nonexistent even in patients who cannot hold their breath. This overview presents a strategy for prudent management of MDCT examinations and describes examination of the most important and frequent renal diseases using MDCT.

Kontrastverst�rkte Sonographie der Leber

The detection rate of liver lesions using ultrasonography is 53-77%, rendering this method inferior to CT and MRI. Despite well-known limitations, development of stable second-generation contrast agents in conjunction with new techniques of contrast display has led to increased diagnostic accuracy. Characterization of focal liver lesions with ultrasound contrast agents follows known features of iodine- and gadolinium-containing contrast agents, but compared to CT and MRI sensitive visualization of intratumoral vessels takes place in real time. In addition to very high diagnostic accuracy in differentiating benign from malignant lesions, detectability of tumors of nonhepatocellular origin is increased significantly and direct assessment of treatment success with minimally invasive tumor ablative interventions in the liver is possible. The active principle of ultrasound contrast agents, examination technique as well as distinguishing features and appearance of various, frequently observed focal liver lesions are illustrated by cases from our department.

Findings and clinical course of a localized primitive peripheral neuroectodermal tumor of the kidney

Primitive neuroectodermal tumor (PNET) is a very aggressive neoplasm, considered to have an unfavorable prognosis, and renal location is extremely rare. We present the findings and clinical course of a patient with localized disease who is free of disease more than 3 years after first presentation. In suspicious cases we recommend to surgically explore renal masses as early as possible.

Abdominal multidetector row computed tomography: reduction of cost and contrast material dose using saline flush

OBJECTIVE

To evaluate the potential of a saline solution flush after the contrast material bolus in abdominal multidetector row CT (MDCT) in contrast material dose and cost reduction.

METHODS

Abdominal MDCT was performed in 78 patients who were assigned randomly to 2 groups receiving 120 mL nonionic contrast material (300 mgI/mL) alone or 100 mL of the same contrast material pushed with 40 mL of saline solution. Mean attenuation values for both groups were measured in the liver, the spleen, the pancreas, the portal vein, the inferior vena cava, and the abdominal aorta. Cost analyses were performed for both groups.

RESULTS

There was no significant difference in parenchymal and vascular enhancement between both groups. The difference of the enhancement was 2 HU for the liver (P = 0.11), 2 HU for the spleen (P = 0.44), 3 HU for the pancreas (P = 0.38), 9 HU for the portal vein (P = 0.11), 3 HU for the inferior vena cava (P = 0.55), and 10 HU for the aorta (P = 0.06). Taking the costs of contrast material, saline solution, and disposal material into account, 7.30 dollars was saved by the patient using a saline solution flush.

CONCLUSIONS

Using a saline flush after the contrast material bolus in abdominal MDCT allows an iodine dose reduction of approximately 6 g, or 17%, without impairing mean parenchymal and vascular enhancement and a cost reduction of 7.30 dollars per patient.

Improvement of parenchymal and vascular enhancement using saline flush and power injection for multiple-detector-row abdominal CT

The aim of this study was to determine if a saline solution flush following low dose contrast material bolus improves parenchymal and vascular enhancement during abdominal multiple detector-row computed tomography (MDCT). Forty-one patients (24 men and 17 women; mean age 49 years, age range 27-86 years) underwent abdominal MDCT (collimation 4x5 mm, 15-mm table increment, reconstruction interval 5 mm, gantry rotation period 0.8 s) with a single- as well as with a double syringe power injector. Indication for examination were benign and malignant tumors and inflammatory diseases. Patients received 100 ml nonionic contrast material (300 mgI/ml) alone or pushed with 20 ml saline solution. Mean enhancement values for both protocols were measured in the liver, the spleen, the pancreas, the renal cortex, the portal vein, the inferior vena cava and the abdominal aorta. Double syringe power-injector protocol led to significantly higher parenchymal and vascular enhancement than single syringe power-injector protocol (p<0.05). The improvement in mean enhancement of the liver was 9 +/- 9 HU, of the spleen 8 +/- 10 HU, of the pancreas 7 +/- 9 HU, and of the renal cortex 8 +/- 20 HU. The improvement in mean enhancement of the portal vein was 10 +/- 17 HU of the inferior vena cava 8 +/- 13 HU and of the abdominal aorta 10 +/- 17 HU. The use of a double syringe power injector with saline flush following contrast material bolus significantly improves parenchymal and vascular enhancement during contrast-enhanced abdominal MDCT with low iodine doses.

Helical CT of the urinary organs

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.

Quantitative and qualitative analysis of in vivo Doppler signal enhancement of FS-069

RATIONALE AND OBJECTIVES

In vivo lifetime of ultrasound (US) contrast agents is still limited and thus a cause for ongoing investigations of new substances. The purpose of this study was to determine the time intensity changes of the Doppler signals obtained within the femoral vein after two different doses of a new microsphere-based ultrasound contrast agent.

METHODS

Twenty-four healthy male volunteers (mean age, 29; average weight, 76 kg) were included in this study. All underwent a triplex Doppler US examination after an intravenous bolus injection of 0.3 mL and 1.0 mL Optison. To examine the signal enhancement characteristics of this contrast agent the audio signal of the pulsed-wave spectral Doppler US was measured quantitatively using an audio analyzer, whereas velocity-encoded color Doppler examinations were scored qualitatively (score 0-3).

RESULTS

The mean maximal enhancement of the audio signal at a dose of 1.0 mL FS-069 was significantly higher than with a bolus of 0.3 mL FS-069 (29 +/- 2 dB vs. 26 dB +/- 2 dB, P < 0.001). The time-intensity curves after each bolus injection yielded an early peak (one minute after the injection) followed by constantly decreasing signal intensities. The scoring of the velocity-encoded color Doppler US revealed an optimal enhancement (score 2) for 3 minutes and 20 seconds (0.3 mL Optison) and for 6 minutes (1.0 mL Optison), respectively.

CONCLUSIONS

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.

Focal nodular hyperplasia and hepatocellular adenoma of the liver: differentiation with multiphasic helical CT

OBJECTIVE

Differences of attenuation and enhancement patterns in focal nodular hyperplasia and hepatocellular adenoma were evaluated and quantified using triphasic single-slice helical CT.

MATERIALS AND METHODS

Forty-five histologically proven focal nodular hyperplasias in 27 patients and 18 hepatocellular adenomas in six patients were examined with helical CT. Quantitative evaluation included the following: attenuation of lesions, scar, and liver parenchyma during unenhanced, arterial (20 sec after injection), and portal venous phases (70 sec after injection); relative enhancement of lesions and liver (the ratio between attenuation in arterial phase and portal venous phase, respectively, and attenuation in unenhanced phase); and the prevalence of scar and its central vessel in focal nodular hyperplasia.

RESULTS

The study showed no significant difference between mean attenuation values of focal nodular hyperplasia (mean +/- SD, 51.2 +/- 5.9 H) and hepatocellular adenoma (mean +/- SD, 56.3 +/- 7.8 H) in the unenhanced phase. In the arterial phase attenuation values were significantly higher in focal nodular hyperplasia (mean +/- SD, 117.9 +/- 15.1 H) than in hepatocellular adenoma (mean +/- SD, 80.1 +/- 10.5 H). In the portal venous phase no significant differences in attenuation values were detected between focal nodular hyperplasia (mean +/- SD, 112.1 +/- 20.4 H) and hepatocellular adenoma (mean +/- SD, 110.2 +/- 12.9 H). For enhancement parameter thresholds separating focal nodular hyperplasia from hepatocellular adenoma, the following were found: the relative enhancement was higher in 100% of the focal nodular hyperplasias and lower than or equal to 1.6 (accuracy, 96%) in 87% of the hepatocellular adenomas.

CONCLUSION

Triphasic helical CT combined with quantitative evaluation of liver lesions offers the possibility of detecting differences in liver lesions that are visually similar on CT. The attenuation and relative enhancement in the arterial phase show significant differences that make accurate differentiation between focal nodular hyperplasia and hepatocellular adenoma possible.

[Current status of diagnostic imaging of focal nodular hyperplasia of the liver]

Ranging behind hemangiomas, focal nodular hyperplasias (FNH) are the second most common benign solid liver lesions. Women between the age of 20 and 50 years are predominantly affected. In rare cases FNH may occur in children. Etiologically, an arteriovenous vascular malformation of the liver is discussed, which causes pseudotumorous growth of the surrounding liver parenchyma. Morphological features such as the presence of a radial vascular architecture and feeding arteries within a central scar are characteristic for the presence of FNH. Imaging techniques which enable the depiction of the arterial blood supply with a characteristic centrifugal filling pattern, the contrast enhancement in the early arterial phase, the absence of calcifications and of a tumour capsule and the typical enhancement of the central scar, are of particular importance. Knowledge of these features is important in order to differentiate FNH from other hypervascular focal liver lesions with tendency of scar formation, such as hepatic adenomas, giant hemangiomas, hepatocellular and fibrolamellar carcinomas, and metastases. Diagnosis and differential diagnosis of FNH will be enabled by a combined modality approach consisting of (Doppler) sonography and triphasic CT. To confirm the diagnosis of FNH, dynamic MRI is advisable. Because of the invasiveness of angiography as well as the limited sensitivity and spatial resolution of the various scintigraphic methods, these modalities no longer play a role in the diagnostic work-up of FNH. Lesions lacking typical features diagnostic for FNH remain subjects for biopsy and histological examination.

Computed tomography densitometry of the lung: a method to assess perfusion defects in acute pulmonary embolism

OBJECTIVE

To evaluate the potential of spiral computed tomography (CT) densitometry of the lung to assess segmental perfusion defects in patients with acute pulmonary embolism.

MATERIALS AND METHODS

Ten patients with known segmental or lobar perfusion defects on ventilation/perfusion scintigraphy and with normal findings in the contralateral lung segment underwent spiral CT of the thorax before and after the administration of contrast material. Regions of interest were defined in 14 segments with normal perfusion and in 14 segments with reduced perfusion. Three consecutive densitometry measurements were performed in each segment.

RESULTS

Those segments with reduced perfusion showed a significantly lower mean CT value on the enhanced scans (-813.4 +/- 57.1 Hounsfield units (HU) vs -794.0 +/- 44.8 HU, P = 0.01) and a significantly decreased contrast enhancement (12.3 +/- 18.2 HU vs 29.8 +/- 16.6 HU, P <0.01) when compared to segments with normal perfusion. Measurements from the unenhanced CT scans were not statistically different between segments with reduced and normal perfusion.

CONCLUSIONS

Spiral CT densitometry allows the assessment of at least segmental perfusion defects in patients with acute pulmonary embolism.

Contrast-enhanced spiral CT of the head and neck: comparison of contrast material injection rates

BACKGROUND AND PURPOSE

Contrast-enhanced spiral CT studies of the head and neck are performed frequently using contrast material volumes of approximately 30 g iodine and a scan delay of 30-45 seconds. Because little is known about the effects of contrast material injection rates on tissue enhancement, this was prospectively investigated in our study.

METHODS

Ninety-seven patients underwent spiral CT of the head and neck. Each patient was assigned randomly to one of four groups who received 100 mL of nonionic contrast material (300 mg I/mL) at different monophasic injection flow rates with 1.5, 2, 3, and 4 mL/s. Scanning started after a constant delay of 35 seconds. The attenuation of the carotid artery, jugular vein, and sternocleidomastoid muscle was measured over time and the attenuation of the submandibular and thyroid gland was evaluated. Vascular attenuation of at least 150 HU was considered to be sufficient.

RESULTS

The mean scan time was 33+/-5 seconds. The study, using an injection rate of 2 mL/s, showed the longest time of sufficient overall (arterial and venous) vessel attenuation (27+/-4 seconds, P< or =.008). The injection flow rate did not influence significantly muscular attenuation (mean enhancement during scan time: 9+/-7 HU). The 1.5 mL/s protocol showed the lowest attenuation values of the submandibular gland (81+/-12 HU) and the highest attenuation values of the thyroid gland (164+/-22 HU), but the attenuation of the thyroid gland was not statistically different from that revealed by the 2 mL/s protocol.

CONCLUSION

Using 100 mL of intravenous contrast material with 300 mg I/mL for spiral CT studies of the entire head and neck, the optimal injection flow is 2 mL/s, whereas lower flow rates resulted in insufficient venous enhancement.

Drop metastases in a patient with a chondroid chordoma of the clivus

Metastasising chordomas are extremely rare and only four cases with drop metastases have been reported. We report a patient with an intracranial chondroid chordoma, typically involving the clivus, treated by repeated resection, percutaneous transluminal embolisation and radiosurgery. During follow-up with MRI asymptomatic intradural drop metastases were observed throughout the spine, with transgression of the intervertebral foramen, forming a "dumbbell".

Echo-enhanced Doppler sonography of focal nodular hyperplasia of the liver

Lesions of focal nodular hyperplasia are hypervascular, benign focal liver lesions whose differentiation from other focal liver lesions is of significant clinical relevance. The purpose of this study was to investigate the echo-enhancing agent SHU 508A (Levovist) in the evaluation of focal nodular hyperplasia with Doppler sonography. We examined 49 patients with 71 lesions of focal nodular hyperplasia in the liver with gray scale and power Doppler sonography. In all patients Levovist was administered intravenously in a concentration of 300 to 400 mg galactose per milliliter. Visualization of the feeding vessels and the vascularity of the lesions were evaluated, and the resistive indices in the feeders and the hepatic arteries were assessed. In comparison with unenhanced power Doppler sonography, echo-enhanced power Doppler sonography yields a higher sensitivity in the detection of the feeding artery (97% versus 82%) in focal nodular hyperplasia and in the depiction of the radial vascular architecture in such lesions, especially those located in the left lobe of the liver. Lesions less than 3 cm in diameter do not consistently show a characteristic vascular architecture with echo-enhanced Doppler sonography. The resistive index of the tumor-feeding artery (mean, 0.51 +/- 0.09) is significantly (P < 0.0001) lower than that of the hepatic artery (mean, 0.65 +/- 0.06) and decreases as the size of the focal nodular hyperplasia increases. The administration of Levovist may improve the signal-to-noise ratio and thus visualization of the vascular architecture in focal nodular hyperplasia. Lesions located in the left lobe of the liver, which commonly are subject to disturbing motion artifacts in color Doppler sonography, will significantly benefit from the administration of Levovist. Echo-enhanced power Doppler sonography, however, is not capable of depicting a characteristic vascular pattern in small (< or = 3 cm) lesions of focal nodular hyperplasia that would guarantee a specific diagnosis.

Orbital dirofilariasis: MR findings

Dirofilariasis is a helminthic zoonosis occurring in many parts of the world. We report the findings in a 61-year-old woman who had painless right exophthalmos caused by orbital dirofilariasis. A vivid worm was embedded inside an inflammatory nodule in the right orbit. On T1-weighted MR images, the parasite was visible as a discrete, low-intensity, tubular signal in the center of the nodule surrounded by contrast-enhancing inflammatory tissue.

Cerebral arteriovenous malformations: diagnostic value of echo-enhanced transcranial Doppler sonography compared with angiography

BACKGROUND AND PURPOSE

The purpose of our study was to examine the clinical value of echo-enhanced transcranial power Doppler sonography (EE-TCD), including it ability to assess hemodynamic parameters of the intracranial vasculature, in patients with suspected cerebral arteriovenous malformations (AVMs) and to compare this method with angiography.

METHODS

Sixteen patients with suspected cerebral AVMs were examined with EE-TCD and angiography. As an echo-enhancing agent, SHU 508A (Levovist) was administered intravenously by bolus injection in nine patients and by continuous infusion in seven. Sonograms were reviewed without knowledge of other imaging results and were correlated with angiographic findings.

RESULTS

Angiography showed AVMs in 12 of 16 patients. Eleven lesions were located in the anterior or middle fossa and one was in the posterior fossa. EE-TCD was slightly less sensitive in the detection of AVMs (92%, 11/12 lesions), since in one patient the lacking acoustic window did not allow a transcranial examination. EE-TCD slightly underestimated AVM size compared with angiographic findings but showed feeding arteries with sufficient acoustic properties. In seven patients (58%), angiography revealed a coincidental blood supply from another intracranial or extracranial vessel, which was missed by EE-TCD in all cases. Assessment of peak systolic velocities and resistive indexes resulted in a higher (mean, 191.1 cm/s) and a lower (mean, 45.7%) value, respectively, in the feeding arteries as compared with the contralateral arteries (mean, 101.8 cm/s and 55.6%, respectively). Side-to-side differences were significantly higher in patients with AVMs than in those without a malformation. Signal enhancement was markedly longer with continuous infusion (mean, 520 seconds +/- 28.2) than with bolus injection (mean, 145 seconds +/- 10.5) of the contrast agent.

CONCLUSION

In our limited study group, EE-TCD was a sensitive method for the detection of AVMs, and Levovist proved to be a safe and effective echo-enhancing substance.

[Criteria for ultrasound differentiation of small angiomyolipomas (< or = 3 cm) and renal cell carcinomas]

PURPOSE

The purpose of this prospective study was to analyze whether ultrasound (US) features are helpful for the differentiation and characterization of small solid (< or = 3 cm) renal masses.

MATERIALS AND METHODS

70 small solid (< or = 3 cm) renal masses were evaluated sonographically with respect to size, location, echogenicity, homogeneity, shadowing, hypoechoic rim, and cystic regions. In addition, all masses were evaluated with spiral-computed tomography (CT). A diagnosis of angiomyolipoma (AML) was made when a lesion contained components with attenuation of fat (> -10 HU). The amount of fat and soft tissue of an AML detected on CT was correlated with the presence of shadowing seen on sonography.

RESULTS

10 (29%) of the 35 renal cell carcinomas (RCC) were hyperechoic to renal parenchyma, but no RCC was as echogenic as the renal sinus fat. Acoustic shadowing was only observed in AML. 11 (34%) AML with shadowing tended to have a larger amount of soft tissue. A hypoechoic rim and cystic regions were only found in RCC. 14 of 35 (40%) RCC showed a hypoechoic rim. Cystic regions were found in 12 of the 35 RCC (34%).

CONCLUSIONS

Renal cell carcinomas display a broad range of echogenicities indicating that small RCC (< or = 3 cm) and AML are not definitely distinguishable by their type of echogenicity. The presence of shadowing, a hypoechoic rim, and cystic regions enable differentiation of small (< or = 3 cm) AML from RCC with a high specificity. Accordingly, sonography has the potential to characterize small (< or = 3 cm) hyperechoic renal masses, with high specificity. However, the low sensitivity of these US features may require a CT for accurate diagnosis.

Value of echo-enhanced Doppler sonography in evaluation of transjugular intrahepatic portosystemic shunts

OBJECTIVE

The value of echo-enhanced color and power Doppler sonography in the evaluation of transjugular intrahepatic portosystemic shunts (TIPS) was assessed and compared with that of unenhanced Doppler sonography and portal angiography.

SUBJECTS AND METHODS

In a prospective randomized trial, 31 shunts in 30 patients underwent unenhanced conventional color and power Doppler sonography and portal venography including pressure measurements. The patients were allocated to either echo-enhanced conventional color Doppler sonography or echo-enhanced power Doppler sonography. For echo enhancement, a galactose-based suspension was administered IV. Shunt stenoses, if present, were quantified by percentage of stenosis and correlated with angiography, which was the gold standard. The diagnostic confidence of unenhanced and echo-enhanced Doppler sonography was assessed using a visual analog scale.

RESULTS

In the diagnosis of shunt occlusion, echo-enhanced Doppler sonography yielded a sensitivity and a specificity of 100% and 100%, respectively, compared with 100% and 89%, respectively, for unenhanced Doppler sonography. Our evaluation of hemodynamically significant stenoses (portosystemic gradient > or = 15 mm Hg) found echo-enhanced Doppler sonography to be superior to unenhanced Doppler sonography (sensitivity and specificity of 82% and 83%, respectively, compared with 64% and 80%, respectively). In the detection of a shunt stenosis based on morphologic criteria only, echo-enhanced Doppler sonography yielded a sensitivity and a specificity of 78% and 100%, respectively, compared with 47% and 50%, respectively, for unenhanced Doppler sonography. Power Doppler imaging did not improve diagnostic accuracy but did increase diagnostic confidence for unenhanced Doppler sonography compared with conventional color Doppler sonography. The diagnostic confidence for sonographic evaluation of TIPS was significantly (p < .001) increased and the variability of hemodynamic measurements was markedly decreased with echo-enhanced sonography.

CONCLUSION

Echo-enhanced Doppler sonography provides images of TIPS like those of angiography and allows morphologic assessment of the shunts, complementary to the essential pulsed Doppler waveform analysis that would be performed in a more guided manner. Also, echo-enhanced Doppler sonography significantly increases the sensitivity and specificity in the diagnosis of shunt dysfunction. The high diagnostic confidence and the diminished variability of spectral Doppler measurements may improve acceptance of sonographic evaluation of TIPS. Echo-enhanced Doppler sonography is safe and effective and may reduce the instances in which TIPS sonographic surveillance is nondiagnostic, in which case angiographic assessment is required.

[Benign non-organ-related diseases of the retroperitoneal space]

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.