T. Albrecht

Ultrasonographic detection of focal liver lesions: increased sensitivity and specificity with microbubble contrast agents

Ultrasonography (US) is the first choice for screening patients with suspected liver lesions. However, due to a lack of contrast agents, US used to be less sensitive and specific compared with computed tomography (CT) and magnet resonance imaging (MRI). The advent of microbubble contrast agents increased both sensitivity and specificity dramatically. Rapid developments of the contrast agents as well as of special imaging techniques were made in recent years. Today numerous different US imaging methods exist which based either on Doppler or on harmonic imaging. They are using the particular behaviour of microbubbles in a sound field which varies depending on the energy of insonation (low/high mechanical index, MI) as well as on the properties of the agent themselves. Apart from just blood pool enhancement some agents have a hepatosplenic specific late phase. US imaging during this late phase using relatively high MI in phase inversion mode (harmonic imaging) or stimulated acoustic emission (SAE; Doppler method) markedly improves the detection of focal liver lesions and is also very helpful for lesion characterisation. With regards to detection, contrast enhanced US performs similarly to CT as shown by recent studies. Early results of studies using low MI imaging and the newer perfluor agents are also showing promising results for lesion detection. Low MI imaging with these agents has the advantage of real time imaging and is particularly helpful for characterisation of focal lesions based on their dynamic contrast behaviour. Apart from the techniques which based on the morphology of liver lesions there were some attempts for the detection of occult metastases or micrometastases by means of liver blood flow changes. Also in this field the use of US contrast agents appears to have advantages over formerly used non contrast-enhanced methods although no conclusive results are available yet.

16-MDCT Angiography of Aortoiliac and Lower Extremity Arteries: Comparison with Digital Subtraction Angiography

OBJECTIVE The objective of our study was to prospectively compare CT angiography (CTA) performed on a 16-MDCT scanner and digital subtraction angiography (DSA) in patients with peripheral arterial disease. SUBJECTS AND METHODS CTA and DSA were compared in 50 patients. CTA was independently evaluated by two blinded observers. DSA was evaluated by two additional blinded observers in consensus. Consensus DSA served as the reference standard for comparisons with CTA in terms of diagnostic quality, grading of stenoocclusive lesions, visualization of collaterals, impact on patient management, and time required for analysis. RESULTS No significant differences in diagnostic quality were observed between CTA and DSA above the ankle; both CTA observers noted significantly better visualization of pedal arteries (70 and 72 segments, respectively) than on DSA (57 segments). Of 958 stenoocclusive lesions on DSA, CTA observers 1 and 2 detected 933 and 929 lesions, respectively. Sensitivity and specificity for the detection of hemodynamically relevant (> 50%) lesions was 93.3% and 96.5% for observer 1 and 90.1% and 95.6% for observer 2. Collaterals were seen at 150 arterial levels on DSA compared with 97 and 92 levels on CTA (p < 0.05, both observers). Patient management decisions based on CTA were equivalent to those based on DSA in 49 of the 50 patients. CONCLUSION CTA is an effective noninvasive alternative to DSA for the evaluation of peripheral arterial disease.

Dual energy CT of peripheral arteries: Effect of automatic bone and plaque removal on image quality and grading of stenoses

PURPOSE To evaluate the effect of automatic bone and plaque removal on image quality and grading of steno-occlusive lesions in patients undergoing dual energy CT angiography (CTA) of lower extremity. MATERIALS AND METHODS Dual energy (DE) runoff CTA was performed in 50 patients using the following parameters: collimation 2 x 32 x 0.6; tube potentials, 80 kV and 140 kV; reconstructed slice thickness 1mm. 100 mL iomeprol 400 and 50 mL saline were injected at 4 mL/s. Separate datasets were calculated for each of the two tubes and used to generate automatically bone-subtracted images (ABS) as well as bone and plaque subtracted images (ABPS). Residual bone in the ABS dataset was removed manually (=ABS-B dataset). In addition, a weighted average dataset from both dual energy acquisitions resembling a routine 120 kV CT acquisition was used for standard manual bone subtraction (MBS). Operator time for bone removal was measured. Effectiveness of bone subtraction and presence of vessel erosions was assessed by two readers in consensus. Stenosis grading in plaque subtracted and unsubtracted images was assessed and correlated. RESULTS Residual bone fragments (ribs: 46%, patella: 25%, spine: 4%, pelvis: 2%, tibia 2% of patients) were only observed with ABS. The time needed to manually remove these residual bones was 2.1+/-1.1 min and was significantly lower than the duration of manual bone removal (6.8+/-2.0 min, p<0.0001, paired t-test). A total of 1159 arteries were analyzed. Compromising vessel erosions were observed less frequently in the ABS-B dataset (10.6%) than in the MBS dataset (15.2%, p<0.001, wilcoxons signed rank test). A total of 817 steno-occlusive lesions were assessed. While the agreement of grading of steno-occlusive lesions was good at the levels of the aorta and the pelvic arteries (kappa=0.70 in both, Cohens kappa statistics), it was moderate at the level of the thigh arteries (kappa=0.57) and poor at the level of the calf (kappa=0.16). CONCLUSION DE CTA has substantial advantages over conventional CTA. Automatic bone subtraction is more time efficient and reliable. Automatic plaque subtraction for the first time provides a true CTA-luminogram which is easy to interpret and reduces the need for further post-processing. DE CTA provides best results in arteries of the thigh; below the knee, plaque subtraction is less accurate.

Low contrast dose voiding urosonography in children with phase inversion imaging

Voiding urosonography (VUS) using a microbubble contrast agent has been introduced as an alternative technique in the diagnosis of vesicoureteral reflux (VUR). This study was undertaken to assess if phase inversion ultrasound (PIUS), a recent microbubble specific imaging technique, has advantages over fundamental in VUS and if it allows a reduction of contrast agent dose. Forty-three children with suspected VUR (aged 3 days–12 years, average of 3.9 years) with 92 kidney-ureter units (KUU) were included. Everyone obtained a baseline US scan that was followed by VUS using Levovist as the contrast agent. Constant switching between fundamental and PIUS performed the enhanced part for comparison. Every child underwent VCUG immediately afterwards. Contrast enhancement was stronger and longer lasting on PIUS than on fundamental US in all 43 cases. Reflux was detected in a total of 21 KUU, out of 92 KUU (23%). PIUS revealed VUR in 18; fundamental in 14 KUU and VCUG depicted 16 cases of reflux (p≥0.29). The mean volume of Levovist dose administered to the bladder was 7.4±3.4% of the bladder volume. VUS using PI mode provided considerably stronger and longer enhancement and slightly improved the detection of VUR. It allowed a reduction of contrast dose and cost by approximately 35% over current dose recommendations for fundamental US.

Do the cardiovascular risk profile and the degree of arterial wall calcification influence the performance of MDCT angiography of lower extremity arteries

ObjectivesTo retrospectively assess the influence of arterial wall calcifications on the accuracy of run-off computed tomographic angiography (CTA) and to analyse whether cardiovascular risk factors are predictors of compromising calcifications.MethodsIn 200 consecutive patients who underwent run-off CTA, calcifications were assessed in pelvic, thigh and calf arteries using a four-point scale. Fifty-nine patients with digital subtraction angiography (DSA) were assessed by both techniques to estimate a threshold of compromising calcifications, defined as a decrease of sensitivity, specificity, PPV or NPV below the lower 95% confidence interval of overall results. Regression analysis was performed to investigate a potential relationship between compromising calcifications and presence of cardiovascular risk factors, advanced patient age and severe peripheral arterial disease (PAD).ResultsThe highest Ca++-score was chosen as the cut-off for the regression analysis, as a relevant decrease of specificity (0.91; overall: 0.95) above the knee and of sensitivity (0.66; overall: 0.83), specificity (0.65; overall: 0.93), positive predictive value (PPV) and negative predictive value (NPV) below the knee was observed. In the pelvic and thigh arteries, severe PAD (Fontaine Stage ≥III) showed the highest odds ratio for compromising calcifications (2.9), followed by diabetes mellitus (2.4), renal failure (2.1) and smoking (1.7). In the calf, renal failure (12.2) and diabetes mellitus (3.3) were the strongest predictors.ConclusionsPatients with diabetes and renal failure should be considered as candidates for alternative vessel imaging in order to avoid inconclusive examination results.

Hepatic transit time analysis using contrast-enhanced ultrasound with BR1: A prospective study comparing patients with liver metastases from colorectal cancer with healthy volunteers.

We prospectively compared hepatic transit time (HTT) measurements in subjects with liver metastases from colorectal cancer (group a) and healthy volunteers (group b) using contrast-enhanced ultrasound with BR1. The purpose of this study was to verify our hypothesis that the hemodynamic changes of the liver, which occur during metastasis seeding, would shorten the HTT, and we expect that such changes could be used for the detection of occult liver metastases from colorectal cancer in the future. The study had institutional review board approval and all subjects gave informed written consent. Group a and group b consisted of 22 subjects each. Baseline and post contrast images were acquired starting 10 s before and ending 40 s after administration of BR1, using nonlinear imaging at a frame rate of 5/s. The baseline images were used to determine the signal intensity without contrast enhancement as the reference signal. Arrival times (AT) of the contrast agent for the hepatic artery, the portal vein and one hepatic vein were determined using (i) quantitative analysis and (ii) subjective analysis by two blinded readers. HTT was calculated based on arrival time measurements. Quantitative and subjective analysis showed significantly shorter arterial to venous and portal to venous HTT in group a compared with group b (p < 0.001). Arterial to venous HTT (quantitative analysis) was < or = 9 s in 19 of 22 subjects of group a and >9 s in 18 of 22 subjects of group b (sensitivity 86%, specificity 82%, positive predictive value 83%, negative predictive value 86%, area under the curve [AUC] 0.87). Portal to venous HTT (quantitative analysis) was < 7 s in 21 of 22 subjects of group a and > 7s in 15 of 22 subjects of group b (sensitivity 95%, specificity 68%, PPV 75%, NPV 94%, AUC 0.85). There was an inverse relation with number of liver segments involved for arterial to venous and portal to venous HTT in group a (p < 0.05), but no correlation between HTT and overall volume of metastases (group a) or subject age (group b). From the results of our study, we conclude that HTT measurements using contrast-enhanced ultrasound with BR1 can detect hemodynamic changes caused by metastatic liver disease from colorectal cancer. However, comparison with the literature suggests that the use of other contrast agents might provide better results. Comparison of different contrast agents for the purpose of transit time analysis would therefore be useful before embarking on a prospective trial looking at the detection of occult liver metastases in patients with colorectal cancer. (E-mail: jhohmann@uhbs.ch).

Using recombinant activated factor VII, B-Lynch compression, and reversible embolization of the uterine arteries for treatment of severe conservatively intractable postpartum hemorrhage: new method for management of massive hemorrhage in cases of placenta increta

OBJECTIVE To investigate a new method for management of massive postpartum hemorrhage in cases of abnormal placenta adhesion. DESIGN Case report. SETTING University hospital. PATIENT(S) An 18-year-old nullipara presented with fulminant postpartum bleeding after cesarean section due to placenta increta. The patient developed hemorrhagic and septic shock associated with disseminated intravascular coagulation. INTERVENTION(S) Treatment with uterotonic drugs like oxytocin and prostaglandins and conservative procedures like transfusion of packed red cells and fresh frozen plasma failed to control the diffuse bleeding. Further intervention consisted of B-Lynch sutures, recombinant activated factor VII, and reversible embolization of the uterine arteries. RESULT(S) The bleeding stopped after operative B-Lynch compression and recombinant activated factor VII. In the interval, the bleeding continued under therapeutically resistant disseminated intravascular coagulation, and finally bilateral reversible embolization of the uterine arteries was performed to avoid an emergency hysterectomy to preserve fertility in this young woman. CONCLUSION(S) This is a case of abnormal placenta adhesion with massive postpartum hemorrhage in which different conservative and operative treatments were combined to avoid a hysterectomy with loss of fertility and major psychological impact for the young mother.

[Dual energy CT of the peripheral arteries: a phantom study to assess the effect of automatic plaque removal on stenosis grading].

PURPOSE To evaluate the accuracy of dual energy (DE)-based plaque removal in a vessel phantom. MATERIALS AND METHODS Acrylic vessel phantoms of different diameters (3, 5, 8 mm), degrees of stenoses (25 - 100%) and plaque densities (300 - 750 HU) were filled with contrast-enhanced blood (150 - 450 HU). Dual source CT was used for simultaneous image acquisition at 80 and 140 kV. Beside a DE-based plaque-subtracted dataset (DE-PS), a virtual 120 kV non-plaque subtracted dataset (N-PS) was generated. Agreement between the known and measured luminal diameter in both datasets was determined using Lins concordance correlation coefficient (kappaLin). RESULTS A total of 8260 measurements were taken. The correlation of measured diameter in DE-PS images was excellent (kappaLin = 0.83 - 0.96) for 5 - 8 mm vessel phantoms with high luminal enhancement (300 - 450 HU) and plaque density (500 - 750 HU), moderate (kappaLin = 0.6 - 0.67) for 5 mm vessels with lower luminal enhancement and plaque density and poor (kappaLin = 0.10 - 0.64) in the 3 mm vessels. The correlation of N-PS-based stenosis quantification was excellent (kappaLin = 0.86 - 0.99) for 5 - 8 mm vessel phantoms if the contrast between lumen and plaque was above 100 HU. The correlation decreased in 3 mm vessels (kappaLin = 0.45 - 0.93), while the lowest correlation was observed for the lowest contrast between plaque and vessel lumen. CONCLUSION Automatic DE-based plaque removal is highly effective for heavily calcified plaques and high luminal enhancement in larger diameter vessels > or = 5 mm). However, accuracy is limited for low density calcified plaque, lower luminal enhancement and smaller caliber vessels mainly due to poor specificity.

Virtual bronchoscopy guidance system for transbronchial needle aspiration

A system for planning transbronchial needle aspiration (TBNA) based on high-resolution chest CT is presented, comprising 2D axial, coronal or sagittal views and a 3D perspective intra-luminal view of the airways. The biopsy site can be defined interactively on the 2D views, and is displayed as 3D object across the translucent bronchial wall. Reference points can be placed on anatomical landmarks like the carina, which allows measuring 3D distances to viewpoints or to other landmarks. Orientation of the targets can be estimated based on a consistent orientation of the virtual endoscopic view. The system can be used as a pre-interventional planning tool, or simultaneously during the biopsy, in order to select the optimal needle insertion points. The system does not provide registration between the virtual and the real images, and does not require special hardware for tracking or any modifications of the bronchoscope. A phantom study comprising three bronchoscopists with different levels of experience showed a significant increase in yield compared to the traditional procedure based on axial CT images alone.

Comparison of a standard and a high-concentration contrast medium protocol for MDCT angiography of the lower limb arteries.

PURPOSE To prospectively compare a compact bolus (CB) injection protocol using high-iodine concentration contrast medium with a standard bolus (SB) injection protocol at equi-iodine doses for run-off computed tomographic angiography (CTA). MATERIALS AND METHODS 64 patients with suspected peripheral arterial disease who underwent 40 or 64-slice run-off CTA were included in this IRB-approved study. Patients were randomized to undergo the CB protocol (32 patients, iomeprol 400mgI/mL, 100 mL, 4 mL/sec) or the SB protocol (32 patients, iomeprol 300mgI/mL, 134 mL, 4 mL/sec). Luminal contrast density (CD) values were measured and arterial opacification (AO) was scored (5-point scale). Cases of venous overlay or bolus overriding were documented. RESULTS Overall arterial CD was significantly higher with the compact bolus (CB: 279 ± 57HU, SB: 234 ± 32HU, p = 0.0017). Segmental CD was significantly higher (p< 0.05) in 7 of 16 evaluated segments. Patency-based comparison revealed superior AO in vessels with relevant (50 - 99 %) stenoses (CB: 4.54 vs. SB: 4.18, p = 0.04). Contrast bolus overriding without pathological reasons, i. e., acute occlusions, was noted in one patient in each group. Venous overlay was observed less frequently in the CB group (CB vs. SB: 12 vs. 19 patients, n. s.; 29 of 64 legs [45 %] vs. 44 of 64 legs [69 %], p = 0.01). CONCLUSION At equi-iodine doses, the CB protocol led to a quantitatively and qualitatively higher arterial opacification compared to the SB protocol. Therefore, a CB protocol should be favored for run-off CTA.