Multi-atlas based segmentation of brain images: atlas selection and its effect on accuracy.

Quantitative research in neuroimaging often relies on anatomical segmentation of human brain MR images. Recent multi-atlas based approaches provide highly accurate structural segmentations of the brain by propagating manual delineations from multiple atlases in a database to a query subject and combining them. The atlas databases which can be used for these purposes are growing steadily. We present a framework to address the consequent problems of scale in multi-atlas segmentation. We show that selecting a custom subset of atlases for each query subject provides more accurate subcortical segmentations than those given by non-selective combination of random atlas subsets. Using a database of 275 atlases, we tested an image-based similarity criterion as well as a demographic criterion (age) in a leave-one-out cross-validation study. Using a custom ranking of the database for each subject, we combined a varying number n of atlases from the top of the ranked list. The resulting segmentations were compared with manual reference segmentations using Dice overlap. Image-based selection provided better segmentations than random subsets (mean Dice overlap 0.854 vs. 0.811 for the estimated optimal subset size, n=20). Age-based selection resulted in a similar marked improvement. We conclude that selecting atlases from large databases for atlas-based brain image segmentation improves the accuracy of the segmentations achieved. We show that image similarity is a suitable selection criterion and give results based on selecting atlases by age that demonstrate the value of meta-information for selection.

Classifier selection strategies for label fusion using large atlas databases.

Structural segmentations of brain MRI can be generated by propagating manually labelled atlas images from a repository to a query subject and combining them. This method has been shown to be robust, consistent and increasingly accurate with increasing numbers of classifiers. It outperforms standard atlas-based segmentation but suffers, however, from problems of scale when the number of atlases is large. For a large repository and a particular query subject, using a selection strategy to identify good classifiers is one way to address problems of scale. This work presents and compares different classifier selection strategies which are applied to a group of 275 subjects with manually labelled brain MR images. We approximate an upper limit for the accuracy or overlap that can be achieved for a particular structure in a given subject and compare this with the accuracy obtained using classifier selection. The accuracy of different classifier selection strategies are also rated against the distribution of overlaps generated by random groups of classifiers.

Liver microbubble transit time compared with histology and Child-Pugh score in diffuse liver disease: a cross sectional study.

BACKGROUND: A previous pilot study showed that early arrival time of a microbubble in a hepatic vein is a sensitive indicator of cirrhosis. AIM: To see if this index can also grade diffuse liver disease. PATIENTS: Thirty nine fasted patients with histologically characterised disease were studied prospectively. Nine patients had no evidence of liver fibrosis, 10 had fibrosis without cirrhosis, and 20 had cirrhosis (five Child's A, seven Child's B, and eight Child's C). METHODS: Bolus injections of a microbubble (Levovist; Schering, Berlin) were given intravenously, followed by a saline flush. Time intensity curves of hepatic vein and carotid artery spectral Doppler signals were analysed. Hepatic vein transit time (HVTT) was calculated as the time after injection at which a sustained signal increase >10% of baseline was seen. Carotid delay time (CDT) was calculated as the difference between carotid and hepatic vein enhancement. RESULTS: Diagnostic studies were achieved in 38/39 subjects. Both HVTT and CDT became consistently shorter with worsening disease, as follows (means (SD)): HVTT: no fibrosis 44 (25) s, fibrosis 26 (8) s, Child's A 21 (1) s, Child's B 16 (3) s, and Child's C 16 (2) s; CDT: no fibrosis 31 (29) s, fibrosis 14 (6) s, Child's A 8 (1) s, Child's B 4 (4) s, and Child's C 3 (3) s. These differences were highly significant (p<0.001, ANOVA comparison). A HVTT <24 s and a CDT <10 s were 100% sensitive for cirrhosis (20/20 and 18/18, respectively) but not completely specific: 2/8 subjects with fibrosis had CDT values <10 s and 3/9 had HVTT <24 s. CONCLUSION: This minimally invasive test shows promise not only in diagnosing cirrhosis but also in assessing disease severity.

Do different types of liver lesions differ in their uptake of the microbubble contrast agent SH U 508A in the late liver phase? Early experience.

PURPOSE: To compare the uptake of SH U 508A in different types of liver lesions by using stimulated acoustic emission. MATERIALS AND METHODS: Thirty-seven patients with characterized lesions (metastasis, n = 17; hepatocellular carcinoma, n = 4; hemangioma, n = 9; focal nodular hyperplasia, n = 7) received 2.5 g SH U 508A. After 5 minutes, stimulated acoustic emission was elicited by using a previously described method. Liver and/or lesional differences were assessed with videodensitometry (objective conspicuity score), and two observers assessed each lesion by using a six-point scale (subjective conspicuity score). RESULTS: Metastases and hepatocellular carcinoma had low stimulated acoustic emission; median objective conspicuity scores were 70% and 68% (all scores were > or =43%), respectively, and subjective conspicuity scores were 2 or higher for both observers. Hemangiomas had reduced stimulated acoustic emission, with more variability; the median objective conspicuity score was 41% (range, 9%-72%), and the median subjective conspicuity scores were 2 (range, 1-4) and 3.5 (range, 1-5) for observers 1 and 2, respectively. Focal nodular hyperplasia had stimulated acoustic emission comparable to that of the liver in all cases; the median objective conspicuity score was -4.7% (all scores were <6%), and the subjective conspicuity score was 1 or lower for both observers. This finding completely separated focal nodular hyperplasia and malignancies. Significant differences were seen between focal nodular hyperplasia and all other lesion types (P < .05). CONCLUSION: Strong late-phase lesional uptake of SH U 508A is characteristic of focal nodular hyperplasia, is seen in some hemangiomas, and was not observed in malignancies.

Liver lesions: intermittent second-harmonic gray-scale US can increase conspicuity with microbubble contrast material-early experience.

The authors investigated the effect of intermittent second-harmonic gray-scale (ISHGS) ultrasonography (US) with SH U 508A microbubbles on the conspicuity of focal liver lesions. Twenty-three patients were included in the study. Images were analyzed subjectively and quantitatively. Objective lesion conspicuity was increased. In 12 of the 15 patients with liver malignancy, gray-scale defects were seen in previously unsuspected areas. ISHGS US may improve the sensitivity of US for liver lesions.

Hepatic malignancies: improved detection with pulse-inversion US in late phase of enhancement with SH U 508A-early experience.

Twenty consecutive patients with known liver malignancies underwent ultrasonography (US) in conventional B mode and in pulse-inversion mode in the late hepatic-specific parenchymal phase after intravenous administration of SH U 508A, a microbubble US contrast agent. Two experienced readers assessed subjective and objective conspicuity, number of lesions, and smallest lesion diameter in each mode. Subjective and objective conspicuity were improved with pulse-inversion mode, and smaller lesions were depicted with pulse-inversion mode than with conventional B mode, improving the detection of metastases less than 1 cm in size.

[Stimulated acoustic emissions with the ultrasound contrast medium levovist: a clinically useful contrast effect with liver-specific properties]. / Stimulierte akustische Emission mit dem Ultraschall-Kontrastmittel Levovist: Ein klinisch nutzbarer Kontrasteffekt mit leberspezifischen Eigenschaften.

PURPOSE: The purpose of this study was systematically to investigate stimulated acoustic emission (SAE) with the microbubble contrast agent Levovist (Schering AG, Berlin) in vivo with regards to reproducibility, distribution in various organs over time, dependence on technical factors, and influence on the delineation of focal liver lesions. PATIENTS AND METHODS: 2 intravenous injections of 1 g of Levovist were given to 2 dogs and 1-6 injections of 2.5 g Levovist to 5 healthy volunteers and 37 patients. The liver, spleen, large abdominal vessels, and kidney were intermittently scanned for up to 30 min. Studies were evaluated for the presence of SAE signals by 2 observers. In 20 patients with focal liver lesions (15 with metastases, 4 haemangiomata, 1 hepatocellular carcinoma, and 1 cyst) the influence on lesion visualization was also assessed. RESULTS: SAE effects, lasting up to 30 minutes, were seen in all subjects in the liver and spleen. Vascular and renal SAE signals were noted shortly after injection, lasting up to 6 minutes. SAE was absent or markedly reduced in focal liver lesions, which were seen as colour voids. This increased the conspicuity of focal lesions, and in 5 patients additional metastases were detected that could not be delineated on B-mode alone. CONCLUSION: A liver- and spleen-specific late phase of Levovist can be consistently demonstrated using SAE and the effect increases the conspicuity of focal liver lesions.

Pulse-inversion mode imaging of liver specific microbubbles: improved detection of subcentimetre metastases.

Pulse-inversion mode (a new ultrasound mode) can be used to image the late liver-specific parenchymal phase of the microbubble contrast-agent Levovist. Scanning in pulse-inversion mode after Levovist improves the detection of liver metastases and reveals more lesions of smaller size than conventional ultrasonography and computed tomography.

Stimulated acoustic emission to image a late liver and spleen-specific phase of Levovist in normal volunteers and patients with and without liver disease.

Quantitative studies were performed to investigate liver- specific uptake of the microbubble Levovist, using stimulated acoustic emission (SAE), which can detect microbubbles even when stationary or slow-moving. These comprised studies of biodistribution comparing the liver and kidney in five normal volunteers, reproducibility in 34 patients, comparison between cirrhotics and controls (n = 9 each) and maximal depth of effect at different frequencies (180 measurements in 31 patients). Stimulated acoustic emission lasted beyond 30 min, with strongly liver-specific properties in each volunteer and was highly reproducible. No difference in the amount of SAE in the superficial liver was seen between cirrhotic and normal livers, but attenuation was higher in cirrhotics. This demonstrates a frequency-dependent effect on liver SAE penetration. We conclude that the liver uptake of Levovist lasts over 30 min, is reproducible, occurs even where diffuse liver disease is present and can be used to assess tissue attenuation in a novel fashion.

[Angioplasty in the stenosed hemodialysis shunt: experiences with 100 patients and 166 interventions]. / Angioplastie am stenosierten Hämodialyseshunt: Erfahrungen an 100 Patienten mit 166 Eingriffen.

PURPOSE: Failing dialysis fistulas are a severe complication for patients treated by chronic haemodialysis. This study was undertaken to evaluate the technical aspects of percutaneous transluminal angioplasty (PTA) of shunts and to report on our experience in 100 patients. PATIENTS AND METHODS: In a 4-year period a total of 166 PTA procedures was performed in 100 haemodialysis patients with stenosis and occlusion of Brescia Cimino shunts and PTFE grafts (polytetrafluoroethylene). Patency rates were retrospectively evaluated for type and location of lesions, patient age, sex and the success of PTA. RESULTS: Technical success was achieved in 97% (n = 161). Complications appeared in 11 cases (6.6%). Shunt occlusion or rupture of a vein is rare. The cumulative patency rate for primary PTA treatment was 55% at 6 months, 47% at 12 months and 32% at 24 months and for repeat PTA treatment 87% at 6 months, 80% at 12 months and 70% at 24 months. Residual stenosis and diabetes mellitus significantly reduced the patency rate. CONCLUSION: PTA is an ideal method for accomplishing recurrent fistula failure due to its cost effectiveness and minimally invasive procedure. Recurrent stenosis has been a major problem of PTA as also in equal measure with surgical intervention.

[Fine-needle biopsy of the kidneys]. / Feinnadelbiopsie der Nieren.

The methods, indications, results, and complications in fine-needle puncture of the kidneys are discussed, with particular attention to cysts that have an atypical appearance in tomographic procedures. The problems of percutaneous cyst treatment and the possibilities of abscess therapy by fine-needle puncture are presented. The limited indications of using this method in solid kidneys tumors are defined, and antegrade pyelography and the differentiation of perirenal processes are discussed.

[Abscess therapy by ultrasound-guided fine needle puncture. 2]. / Abszesstherapie durch ultraschallgeführte Feinnadelpunktion. 2. Mitteilung.

29 intraabdominal abscesses were punctured with sonographic guidance. 26 cases were treated by an evacuating needle puncture which was curative in 23 cases (88%). The complications were temporary bacteraeminas in two cases, which were managed conservatively. Sonographically guided fine needle puncture is a simple and effective procedure for the treatment of abdominal abscesses and should be considered as an alternative to surgery and percutaneous drainage.

[Therapeutic results of ultrasonically-guided kidney cyst punctures]. / Therapeutische Ergebnisse der ultraschallgeführten Nierenzystenpunktion.

The behaviour of renal cysts following puncture was studied in 62 patients on whom a simple diagnostic puncture had been performed and on fourteen patients who, in addition, had some of their own blood injected into the cyst. Twenty-one patients (34%) of the first group and eight patients (57%) of the second group showed definite reduction in the size of the renal cyst after an average period of observation of fifteen months. In 7%, the cyst disappeared completely following puncture. Parapelvic cysts showed much less tendency to disappear than did cortical cysts. The results of injecting autologous blood are comparable with those of injecting lipid soluble contrast media as a sclerosing agent. Before surgical removal of a symptomatic renal cyst is contemplated, puncture and evacuation of the cyst with autologous blood injection is recommended.

[Renal tumor diagnosis with ultrasound and CT]. / Renale Tumordiagnostik mit Ultraschall und CT.

The use of sonography and computer tomography has resulted in a marked change in the diagnosis of renal space occupying lesions. The value of these diagnostic tests is analyzed mainly in the diagnosis of solid kidney tumors. The possibilities and limitations are analyzed and the addition of further diagnostic procedures such as fine needle puncture and operative exploration are considered. A proper diagnostic work-up is outlined.

Treatment of pyogenic splenic abscess by ultrasonically guided fine needle puncture.

One case of pyogenic splenic abscess, diagnosed and treated by several ultrasonically guided fine needle punctures, is presented. This noninvasive procedure provided a definitive therapy preserving the spleen. Evacuating fine needle puncture seems to be an alternative therapy of splenic abscess, especially in patients with reduced operability.

[Embolization therapy of primary soft tissue tumors and metastatic masses in the pelvic region. Indications, results and risks]. / Embolisations-Therapie von primären Weichteiltumoren und metastatischen Raumforderungen im Beckenbereich. Indikation, Ergebnisse und Risiken.

Report of 11 cases of soft tissue and metastatic tumors of the pelvis which had been treated by transcatheter - embolization in the pre-operative phase. The complication rate exceeds 25%. This complications are, as to our opinion - due to the administration of alcohol. For this reason we prefer polyacrylic agents such as Ethibloc.

Sonography of infantile polycystic kidney disease.

Seven children aged 1 day to 12 years with infantile polycystic kidney disease (IPCD) were evaluated by a new high-resolution real-time ultrasound scanner. Instead of the monotonous increased echogenicity of renal parenchyma seen with earlier ultrasound equipment, the echo texture of IPCD became more differentiated, showing disseminated tiny cysts associated with high-amplitude echoes. Even in the newborn, cysts as small as 2 mm in diameter could be detected. Analysis of the new sonographic features of IPCD reveals specific "pepper and salt" and "striped" patterns. In association with such well-known sonographic findings as bilateral enlarged kidneys and poor definition of renal sinus, medulla, and cortex, this pattern allows one to make the final diagnosis of IPCD.

[Ultrasound-guided thin-needle biopsy in focal liver diseases. I. Malignant hepatic tumors]. / Ultraschallgeführte Feinnadelbiopsie herdförmiger Lebererkrankungen. Teil I: Maligne Lebertumoren.

Eighty-six patients with focal liver disease underwent sonography-guided percutaneous fine needle biopsy for definitive diagnosis. Twenty-five out of twenty-six neoplastic liver tumors were correctly recognized as malignant. A sensitivity of 96% and a specificity of 98% (25 true positives, 60 true negatives, 1 false negative) was obtained. The high accuracy rate of this diagnostic procedure is explained by the precision of sonographic guidance and the copious excision of tissue material. In 57% of the malignant tumors, small tissue cylinders were obtained besides cytological material, which allowed a definitive tumor diagnosis in 11 out of 15 cases by histologic examination. In addition, the histologic evaluation of tissue fragments enables the differentation between primary and secondary hepatic malignomas. Because of the higher specificity of histological diagnosis, fine needle puncture of solid liver tumors should always provide tiny tissue cylinders for histologic examination.