Spatial Coherence in Medical Ultrasound: A Review

Traditional pulse-echo ultrasound imaging heavily relies on the discernment of signals based on their relative magnitudes but is limited in its ability to mitigate sources of image degradation, the most prevalent of which is acoustic clutter. Advances in computing power and data storage have made it possible for echo data to be alternatively analyzed through the lens of spatial coherence, a measure of the similarity of these signals received across an array. Spatial coherence is not currently explicitly calculated on diagnostic ultrasound scanners but a large number of studies indicate that it can be employed to describe image quality, to adaptively select system parameters and to improve imaging and target detection. With the additional insights provided by spatial coherence, it is poised to play a significant role in the future of medical ultrasound. This review details the theory of spatial coherence in pulse-echo ultrasound and key advances made over the last few decades since its introduction in the 1980s.

The Impact of Acoustic Clutter on Large Array Abdominal Imaging

Abdominal imaging suffers from a particularly difficult acoustic environment-targets are located deep and overlying tissue layers with varying properties generate acoustic clutter. Increasing array size can overcome the penetration and lateral resolution problems in ideal conditions, but how the impact of clutter scales with increasing array extent is unknown and may limit the benefits in vivo. Previous ex vivo experimental work showed the promise of large arrays but was technically limited to a length of 6.4 cm and to only partial sampling of the array elements. We present an extension of those studies using the Fullwave simulation tool to create a 10 cm ×2 cm matrix array with full lateral element sampling. We used a numerical model of the abdomen based on the maps of tissue acoustical properties and found that propagation through the modeled abdominal layers generated on average 25.4 ns of aberration and 0.74 cm of reverberation clutter across the array extent. Growing the full aperture from 2 to 10 cm improved contrast by 8.6 dB and contrast-to-noise ratio by 22.9% in addition to significantly improving target resolution. Alternative array strategies that may be useful for implementation-mismatched aperture sizes or a swept synthetic aperture-also produced improved quality with growing aperture size. These results motivate the development of larger diagnostic imaging arrays for the purpose of high-resolution imaging in challenging environments.

Multiphysics modeling toward enhanced guidance in hepatic microwave ablation: a preliminary framework

We compare a surface-driven, model-based deformation correction method to a clinically relevant rigid registration approach within the application of image-guided microwave ablation for the purpose of demonstrating improved localization and antenna placement in a deformable hepatic phantom. Furthermore, we present preliminary computational modeling of microwave ablation integrated within the navigational environment to lay the groundwork for a more comprehensive procedural planning and guidance framework. To achieve this, we employ a simple, retrospective model of microwave ablation after registration, which allows a preliminary evaluation of the combined therapeutic and navigational framework. When driving registrations with full organ surface data (i.e., as could be available in a percutaneous procedure suite), the deformation correction method improved average ablation antenna registration error by 58.9% compared to rigid registration (i.e., 2.5 ± 1.1    mm , 5.6 ± 2.3    mm of average target error for corrected and rigid registration, respectively) and on average improved volumetric overlap between the modeled and ground-truth ablation zones from 67.0 ± 11.8 % to 85.6 ± 5.0 % for rigid and corrected, respectively. Furthermore, when using sparse-surface data (i.e., as is available in an open surgical procedure), the deformation correction improved registration error by 38.3% and volumetric overlap from 64.8 ± 12.4 % to 77.1 ± 8.0 % for rigid and corrected, respectively. We demonstrate, in an initial phantom experiment, enhanced navigation in image-guided hepatic ablation procedures and identify a clear multiphysics pathway toward a more comprehensive thermal dose planning and deformation-corrected guidance framework.

Sonography of Acute Cholecystitis and Its Mimics

Right upper quadrant (RUQ) abdominal pain is a common complaint. Acute cholecystitis (AC) is the primary diagnostic consideration in most adults presenting with acute onset RUQ abdominal pain; however, a variety of other conditions can mimic AC. Abdominal ultrasound (US) receives the highest score for imaging appropriateness for these patients. This article reviews the sonographic findings of uncomplicated and complicated AC and provides practical technical tips. The radiologist should be familiar with conditions that can mimic AC, be able to suggest these alternative diagnoses when findings are present on US, and recommend additional tests or procedures, if needed.

Gallbladder Scalloping, Mammillated Caudate Lobe, and Inferior Vena Cava Scalloping: Three Novel Ultrasound Signs of Cirrhosis

PURPOSE

We aimed to present three new ultrasound signs-gallbladder scalloping, mammillated caudate lobe, and inferior vena cava scalloping-and determine their accuracy in diagnosing liver cirrhosis.

MATERIALS AND METHODS

A total of 201 consecutive patients with a history of chronic liver disease who had undergone ultrasound imaging and liver biopsy were identified. A senior ultrasound radiologist blindly reviewed the ultrasound examinations. Specificity, sensitivity, positive predictive value, and negative predictive value of diagnosing cirrhosis were calculated for all evaluated ultrasound signs and selected combinations of signs, using the liver biopsy results as the reference standard.

RESULTS

Of the 201 patients, 152 (76%) had either pathology-proven cirrhosis or significant fibrosis. Caudate lobe hypertrophy was the most specific (88%) and most positive predictor (90%) for cirrhosis, whereas mammillated caudate lobe was the most sensitive (78%). Inferior vena cava scalloping was the most specific (78%) of the three proposed ultrasound signs. When signs were combined, the presence of either gallbladder scalloping or liver surface nodularity was highly sensitive for cirrhosis (87%), whereas the presence of either gallbladder scalloping or inferior vena cava scalloping with caudate lobe hypertrophy was highly specific (93%).

CONCLUSIONS

Gallbladder scalloping, mammillated caudate lobe, and inferior vena cava scalloping are three novel signs that improve the accuracy of ultrasound in diagnosing cirrhosis.

Dietary Melatonin Supplementation Could Be a Promising Preventing/Therapeutic Approach for a Variety of Liver Diseases

In the therapeutic strategies, the role of diet is a well-established factor that can also have an important role in liver diseases. Melatonin, identified in animals, has many antioxidant properties and it was after discovered also in plants, named phytomelatonin. These substances have a positive effect during aging and in pathological conditions too. In particular, it is important to underline that the amount of melatonin produced by pineal gland in human decreases during lifetime and its reduction in blood could be related to pathological conditions in which mitochondria and oxidative stress play a pivotal role. Moreover, it has been indicated that melatonin/phytomelatonin containing foods may provide dietary melatonin, so their ingestion through balanced diets could be sufficient to confer health benefits. In this review, the classification of liver diseases and an overview of the most important aspects of melatonin/phytomelatonin, concerning the differences among their synthesis, their presence in foods and their role in health and diseases, are summarized. The findings suggest that melatonin/phytomelatonin supplementation with diet should be considered important in preventing different disease settings, in particular in liver. Currently, more studies are needed to strengthen the potential beneficial effects of melatonin/phytomelatonin in liver diseases and to better clarify the molecular mechanisms of action.

Evaluation of Large-Aperture Imaging Through the ex Vivo Human Abdominal Wall

Current clinical abdominal imaging arrays are designed to maximize angular field of view rather than the extent of the coherent aperture. We illustrate, in ex vivo experiments, the use of a large effective aperture to perform high-resolution imaging, even in the presence of abdominal wall-induced acoustic clutter and aberration. Point and lesion phantom targets were imaged through a water path and through three excised cadaver abdominal walls to create different clinically relevant clutter effects with matched imaging targets. A 7.36-cm effective aperture was used to image the targets at a depth of 6.4 cm, and image quality metrics were measured over a range of aperture sizes using synthetic aperture techniques. In all three cases, although degradation compared with the control was observed, lateral resolution improved with increasing aperture size without loss of contrast. Spatial compounding of the large-aperture data drastically improved lesion detectability and produced contrast-to-noise ratio improvements of 83%-106% compared with the large coherent aperture. These studies indicate the need for the development of large arrays for high-resolution abdominal diagnostic imaging.

Laparoscopic image-based navigation for microwave ablation of liver tumors-A multi-center study

BACKGROUND

Stereotactic navigation technology has been proposed to augment accuracy in targeting intrahepatic lesions for local ablation therapy. This retrospective study evaluated accuracy, efficacy, and safety when using laparoscopic image-guided microwave ablation (LIMA) for malignant liver tumors.

METHODS

All patients treated for malignant liver lesions using LIMA at two European centers between 2013 and 2015 were included for analysis. A landmark-based registration technique was applied for intraoperative tumor localization and positioning of ablation probes. Intraoperative efficiency of the procedure was measured as number of registration attempts and time needed to achieve sufficient registration accuracy. Technical accuracy was assessed as Fiducial Registration Error (FRE). Outcome at 90 days including mortality, postoperative morbidity, rates of incomplete ablations, and early intrahepatic recurrences were reported.

RESULTS

In 34 months, 54 interventions were performed comprising a total of 346 lesions (median lesions per patient 3 (1-25)). Eleven patients had concomitant laparoscopic resections of the liver or the colorectal primary tumor. Median time for registration was 4:38 min (0:26-19:34). Average FRE was 8.1 ± 2.8 mm. Follow-up at 90 days showed one death, 24% grade I/II, and 4% grade IIIa complications. Median length of hospital stay was 2 days (1-11). Early local recurrence was 9% per lesion and 32% per patient. Of these, 63% were successfully re-ablated within 6 months.

CONCLUSIONS

LIMA does not interfere with the intraoperative workflow and results in low complication and early local recurrence rates, even when simultaneously targeting multiple lesions. LIMA may represent a valid therapy option for patients with extensive hepatic disease within a multimodal treatment approach.

Comparison of the Accuracy of DWI and Ultrasonography in Screening Hepatocellular Carcinoma in Patients With Chronic Liver Disease

Background:

Hepatocellular carcinoma (HCC) is a neoplasm usually arising in a cirrhotic liver by a multistep carcinogenesis process. Early detection of HCC and accurate assessment of tumor burden are crucial to successful treatment planning and long-term survival.

Objectives:

In this study, we compared the accuracy of diffusion weighted imaging (DWI) combined with limited sequence magnetic resonance imaging (MRI) set as a potentially quick and practical MR candidate with ultrasonography (US) for screening of HCC in patients with cirrhosis.

Patients and Methods:

Of 96 patients with cirrhosis, 30 who had concomitant HCC proved by pathology were selected. MRI, DWI, and US of the liver were performed for the patients. Sensitivity, specificity, and accuracy of DWI alone, limited sequences MRI alone, a combination of them, and US were calculated for the detection of HCC in these patients and then comparison between these modalities was performed.

Results:

Combination of limited sequences MRI and DWI had the highest accuracy (94.79%) followed by DWI alone followed by limited sequence MRI alone. The least accuracy was for US (78.12%) with a statistically significant difference.

Conclusion:

Due to the significant improvement in the treatment of early stage of HCC compared to the previous decade, we suggest a fast, non-invasive, more accurate, but more expensive method (HASTE, OP/IP T1W sequences MRI combined with DWI) rather than US for the screening of HCC in liver cirrhosis.

The effectiveness of ultrasound surveillance for hepatocellular carcinoma in a Canadian centre and determinants of its success

BACKGROUND

The effectiveness of surveillance for hepatocellular carcinoma (HCC) using ultrasound (US) in North America has been questioned due to the predominance of patients of Caucasian ethnicity and larger body habitus.

OBJECTIVE

To determine the effectiveness of US surveillance for HCC in a Canadian hepatobiliary centre and to identify independent variables associated with early detection of tumour(s).

METHODS

A retrospective review of patients with first HCC in a US surveillance population at the authors' hospital yielded 201 patients (over a 10.5-year period). Patients were categorized into three groups: regular surveillance (frequency of surveillance ≤12 months [n=109]); irregular surveillance (frequency of surveillance >12 months [n=38]); or first surveillance (tumour detected on first scan [n=54]). The Milan criteria for transplantation and Barcelona Clinic Liver Cancer (BCLC) staging system were used as outcome measures. Effective surveillance was defined as tumour detection within Milan criteria or curative BCLC stages 0 and A; its association with multiple patient- and disease-related variables was tested.

RESULTS

When using the Milan criteria as outcome, 84 of 109 (77%) regular surveillance patients, 23 of 38 (61%) irregular surveillance patients and 40 of 54 (74%) first surveillance patients had tumours meeting the transplantation criteria. The difference between regular and irregular surveillance was statistically significant (P=0.03). When using the BCLC staging system, 87 of 109 (80%) regular surveillance patients, 26 of 38 (68%) irregular surveillance patients and 41 of 54 (76%) first surveillance patients had their tumours detected in BCLC curative stages (0 and A; P=0.11). Regular surveillance was the only variable significantly associated with detection of tumour(s) within the Milan criteria (OR 2.76 [95% CI 1.10 to 6.88]). Tumours detected more recently were more likely to be <2 cm in size (BCLC stage 0; OR 2.38 [95% CI 1.07 to 5.31]).

CONCLUSION

A high rate of HCC surveillance success was achieved using US alone when performed regularly in a specialized hepatobiliary centre.

Evaluation of a minimally invasive image-guided surgery system for hepatic ablation procedures

BACKGROUND

The Explorer Minimally Invasive Liver (MIL) system uses imaging to create a 3-dimensional model of the liver. Intraoperatively, the system displays the position of instruments relative to the virtual liver. A prospective clinical study compared it with intraoperative ultrasound (iUS) in laparoscopic liver ablations.

METHODS

Patients undergoing ablations were accrued from 2 clinical sites. During the procedures, probes were positioned in the standard fashion using iUS. The position was synchronously recorded using the Explorer system. The distances from the probe tip to the tumor boundary and center were measured on the ultrasound image and in the corresponding virtual image captured by the Explorer system.

RESULTS

Data were obtained on the placement of 47 ablation probes during 27 procedures. The absolute difference between iUS and the Explorer system for the probe tip to tumor boundary distance was 5.5 ± 5.6 mm, not a statistically significant difference. The absolute difference for probe tip to tumor center distance was 8.6 ± 7.0 mm, not statistically different from 5 mm.

DISCUSSION

The initial clinical experience with the Explorer MIL system shows a strong correlation with iUS for the positioning of ablation probes. The Explorer MIL system is a promising tool to provide supplemental guidance information during laparoscopic liver ablation procedures.

Curcumin and liver disease

Liver diseases pose a major medical problem worldwide and a wide variety of herbs have been studied for the management of liver-related diseases. In this respect, curcumin has long been used in traditional medicine, and in recent years it has been the object of increasing research interest. In combating liver diseases, it seems clear that curcumin exerts a hypolipidic effect, which prevents the fatty acid accumulation in the hepatocytes that may result from metabolic imbalances, and which may cause nonalcoholic steatohepatitis. Another crucial protective activity of curcumin, not only in the context of chronic liver diseases but also regarding carcinogenesis and other age-related processes, is its potent antioxidant activity, which affects multiple processes and signaling pathways. The effects of curcumin on NF-κβ are crucial to our understanding of the potent hepatoprotective role of this herb-derived micronutrient. Because curcumin is a micronutrient that is closely related to cellular redox balance, its properties and activity give rise to a series of molecular reactions that in every case and biological situation affect the mitochondria.

Diagnosis of hepatocellular carcinoma: newer radiological tools

With the recent dramatic advances in diagnostic modalities, the diagnosis of hepatocellular carcinoma (HCC) is primarily based on imaging. Ultrasound (US) plays a crucial role in HCC surveillance. Dynamic multiphasic multidetector-row CT (MDCT) and magnetic resonance imaging (MRI) are the standard diagnostic methods for the noninvasive diagnosis of HCC, which can be made based on hemodynamic features (arterial enhancement and delayed washout). The technical development of MDCT and MRI has made possible the fast scanning with better image quality and resolution, which enables an accurate CT hemodynamic evaluation of hepatocellular tumor, as well as the application of perfusion CT and MRI in clinical practice. Perfusion CT and MRI can measure perfusion parameters of tumor quantitatively and can be used for treatment response assessment to anti-vascular agents. Besides assessing the hemodynamic or perfusion features of HCC, new advances in MRI can provide a cellular information of HCC. Liver-specific hepatobiliary contrast agents, such as gadoxetic acid, give information regarding hepatocellular function or defect of the lesion, which improves lesion detection and characterization. Diffusion-weighted imaging (DWI) of the liver provides cellular information of HCC and also has broadened its role in lesion detection, lesion characterization, and treatment response assessment to chemotherapeutic agents. In this article, we provide an overview of the state-of-the art imaging techniques of the liver and their clinical role in management of HCC.