Charlotte J. C. Cash

HIGH-DEFINITION FREEHAND 3-D ULTRASOUND

This paper describes a high-definition freehand 3-D ultrasound (US) system, with accuracy surpassing that of previously documented systems. 3-D point location accuracy within a US data set can be achieved to within 0.5 mm. Such accuracy is possible through a series of novel system-design and calibration techniques. The accuracy is quantified using a purpose-built tissue-mimicking phantom, designed to create realistic clinical conditions without compromising the accuracy of the measurement procedure. The paper includes a thorough discussion of the various ways of measuring system accuracy and their relative merits; and compares, in this context, all recently documented freehand 3-D US systems.

Sensorless freehand 3-D ultrasound using regression of the echo intensity

In freehand 3-D ultrasound (US), a position sensor is attached to the probe of a 2-D US machine. The resulting 3-D data permit flexible visualisation and more accurate volume measurement than can be achieved using 2-D B-scans alone; however, the use of the position sensor can be inconvenient for the clinician. The objective is, thus, to replace the sensor with a technique for estimating the probe trajectory based on the B-scan images, themselves. One such technique exists, based on decorrelation algorithms. This paper presents an alternative approach based on linear regression of the echo-envelope intensity signal. A probabilistic analysis of the speckle characteristics of the US signal leads to a linear model, on which the regression algorithm is based. The gradient parameter of this model is shown to be directly related to probe motion. The viability of the new approach is demonstrated through simulations and in vitro and in vivo experiments.

Complications of Continuous Ambulatory Peritoneal Dialysis

Continuous ambulatory peritoneal dialysis (CAPD) is used to treat end-stage renal failure in an increasing number of patients. CAPD has an advantage over hemodialysis in that it allows patients greater freedom to perform daily activities; it also provides other clinical benefits. However, the long-term effectiveness of CAPD is limited by complications, which have various causes. Complications with an infectious cause include bacterial peritonitis, tuberculous peritonitis, and infections of the catheter exit site and tunnel. Noninfectious complications include catheter dysfunction, dialysate leakage, hernias, and sclerosing encapsulating peritonitis. Many imaging modalities-radiography, ultrasonography, peritoneal scintigraphy, computed tomography (CT), and magnetic resonance (MR) imaging-are useful for characterizing these complications. CT peritoneography and MR peritoneography are techniques specifically suited to this purpose. Imaging plays a critical role in ensuring that complications are detected early and managed appropriately.

Rapid registration for wide field of view freehand three-dimensional ultrasound

A freehand scanning protocol is the only way to acquire arbitrary large volumes of three-dimensional ultrasound (US) data. For some applications, multiple freehand sweeps are required to cover the area of interest. Aligning these multiple sweeps is difficult, typically requiring nonrigid image-based registration as well as the readings from the spatial locator attached to the US probe. Conventionally, nonrigid warps are achieved through general elastic spline deformations, which are expensive to compute and difficult to constrain. This paper presents an alternative registration technique, where the warps degrees of freedom are carefully linked to the mechanics of the freehand scanning process. The technique is assessed through an extensive series of in vivo experiments, which reveal a registration precision of a few pixels with comparatively little computational load.

Grey-scale gating for freehand 3D ultrasound

Freehand three-dimensional (3D) ultrasound is a flexible imaging technique which allows a 3D data set to be constructed of sequential B-scans from a conventional ultrasound scanner. Since the data is acquired over several seconds, physiological motion generates spatial artifacts in visualisations of the data. Consequently, an electrocardiogram (ECG) signal is often used to gate the acquisition of B-scans to a single point in the cardiac cycle. We present a technique which can remove temporal artifacts by using properties of the grey-scale B-scan data, obviating the need for an external gating signal. B-scans are acquired throughout the cardiac cycle, and any phase can be selected for subsequent visualisation. This enables limited real-time 4D display of the data.

Can radiological assessment of abdominal computerized scans diagnose encapsulating peritoneal sclerosis in long term peritoneal dialysis patients

Encapsulating peritoneal sclerosis (EPS) is a rare but potentially devastating complication of long‐term peritoneal dialysis (PD). Changes to the peritoneal membrane occur with duration of PD therapy. To determine the potential effect of prospective computerized tomography (CT) scanning, we reviewed the scans of patients who had developed EPS compared with those without EPS.

Using image-based regression to acquire freehand 3D ultrasound

Describes a new technique for estimating the out-of-plane distances between neighbouring 2D B-scan images. Probabilistic analysis of the speckle signal intensity leads to a distance estimation algorithm based on linear regression. The quality of fit to the regression line indicates the reliability of the distance estimate. The new technique can be used to determine the three out-of-plane degrees-of-freedom of scan plane motion. The in-plane translations and rotation can be deduced by correlating neighbouring B-scan images. As a result, the relative 3D positions of all the 2D B-scans can be calculated without the need for a position sensor attached to the ultrasound probe. The approach is useful for recording 3D data when a position sensor is not available, or for improving the local consistency of a conventional sensor-based recording.

Carcinoid tumour presenting as recurrent pneumonia

A 39-year-old woman non-smoker gave a history of three separate episodes of pneumonia over 2 years. Each involved the right lower lobe (figure 1), and clinical plus chest radiographic resolution was achieved following antibiotics. CT of the chest revealed a partially calcified lesion lying externally adjacent to the right lower lobe bronchus causing partial compression …

Imaging in Acute and Chronic Pulmonary Thromboembolic Disease

Acute pulmonary embolism (PE) is the third commonest acute cardiovascular disease. Prompt and accurate diagnosis is important. Significant morbidity and mortality are associated with both false-positive and -negative diagnosis. Although chronic thromboembolic disease (CTED) is an uncommon sequelae of acute PE, it is a potentially curable cause of pulmonary arterial hypertension (PAH) by means of pulmonary endarterectomy. Imaging plays an important role in the surgical work-up of patients with CTED. This chapter reviews the latest recommended algorithms in the diagnosis of acute PE and the role of leg sonography, ventilation-perfusion isotope imaging, computed tomography pulmonary angiography, conventional angiography, magnetic resonance angiography, and high-resolution computed tomography in the diagnosis of both acute and chronic pulmonary thromboembolism.