Suk Yee Ng

Validity of 2D lateral cephalometry in orthodontics: a systematic review

Lateral cephalometric radiography is commonly used as a standard tool in orthodontic assessment and treatment planning. The aim of this study was to evaluate the available scientific literature and existing evidence for the validation of using lateral cephalometric imaging for orthodontic treatment planning. The secondary objective was to determine the accuracy and reliability of this technique. We did not attempt to evaluate the value of this radiographic technique for other purposes. A literature search was performed using specific keywords on electronic databases: Ovid MEDLINE, Scopus and Web of Science. Two reviewers selected relevant articles, corresponding to predetermined inclusion criteria. The electronic search was followed by a hand search of the reference lists of relevant papers. Two reviewers assessed the level of evidence of relevant publications as high, moderate or low. Based on this, the evidence grade for diagnostic efficacy was rated as strong, moderately strong, limited or insufficient. The initial search revealed 784 articles listed in MEDLINE (Ovid), 1,034 in Scopus and 264 articles in the Web of Science. Only 17 articles met the inclusion criteria and were selected for qualitative synthesis. Results showed seven studies on the role of cephalometry in orthodontic treatment planning, eight concerning cephalometric measurements and landmark identification and two on cephalometric analysis. It is surprising that, notwithstanding the 968 articles published in peer-reviewed journals, scientific evidence on the usefulness of this radiographic technique in orthodontics is still lacking, with contradictory results. More rigorous research on a larger study population should be performed to achieve full evidence on this topic.

Ultrasound imaging in the preoperative estimation of the size of tracheostomy tube required in specialised operations in children

BACKGROUND Some children are dependent on a tracheostomy for many years. As they grow, larger tracheostomy tubes may be required. Although tables of sizes of tracheas exist for different age groups, they are estimations of normal and may not be accurate for atypical cases. Chest radiographs and computed tomograms (CT) have been used experimentally to estimate tracheal sizes, but are not in regular use. METHOD High-resolution diagnostic ultrasound imaging was used to estimate the internal and external transverse tracheal diameter, and the depth of the trachea from the skin surface. This allowed selection of the correct standard pattern tracheostomy tube, or the construction of a custom-made tube preoperatively. RESULTS Four children with various abnormalities who were being considered for replacement tracheostomies were scanned. In one, diagnostic ultrasound confirmed that a new larger fenestrated tube could be placed, which subsequently improved vocalisation and respiration. In the other three, the scan showed there was no space to allow a larger tube to be placed. The standard tables were not suitable for any of these patients. CONCLUSION High-resolution ultrasound has a role in the non-invasive measurement of the size of the tube needed for specialised operations in children.

Diagnostic ultrasound patterns of parotid glands in human immunodeficiency virus-positive patients in Mulago, Uganda

OBJECTIVES The purpose of this study was to determine sonographically, in parotid glands of human immunodeficiency virus-positive patients, the condition of glands with or without enlargement, and propose a classification system for the patterns observed using diagnostic ultrasound imaging. METHODS In this prospective clinical study, ultrasound scans were performed on 200 patients aged 4-62 years at Mulago Hospital, Uganda. RESULTS There were four main distinct ultrasound pathological patterns in the parotids, i.e. lymphocytic aggregations (LAs), lymphoepithelial cysts (LECs), fatty infiltration (FI) and lymphadenopathy only. There were additional subdivisions depending on the presence of echogenic foci and intraparotid lymphadenopathy. Of those patients (n = 64) without parotid enlargement, only 8% showed normal ultrasound features, whereas 34% showed LECs and 31% showed LAs. Of those (n = 136) with parotid enlargement, 46% showed LECs, 23% showed FI and 15% showed LAs. The overall prevalence of LECs in the study sample was 42%. LECs were multiple, mainly between 7 mm and 12 mm in diameter and 26% showed internal echogenic foci either mobile or stationary. In contrast, LAs tended to be ill-defined, less than 5 mm and were not associated with posterior acoustic enhancement. Features differentiating LAs from LECs have not been previously described. Parotid FI (lipodystrophy) was noted in patients on highly active antiretroviral therapy, who showed lesser prevalence of LECs after 12 months of treatment. CONCLUSIONS Our study of 200 patients is probably the largest such study in the English language literature. The wide spectrum of diagnostic ultrasound patterns was categorized into four main groups (ten subgroups).

PVdF array characterisation for high frequency ultrasonic imaging

Polyvinylidenefluoride (PVdF) has been utilized for a number of years within ultrasonic hydrophones. However, polymeric materials have rarely been incorporated into medical imaging phased arrays due to lower emitted power levels (relative to PZT transducers), and higher transducer element impedance. PVdFs advantages as a transducer material lie in its inherent wide bandwidth and the potential to create high-resolution images whilst maintaining low transducer manufacturing costs. Here we report the fabrication and test of PVdF linear arrays with 28 /spl mu/m PVdF film with elements on a 250 /spl mu/m pitch. These arrays are connected to equipment that has been developed to perform transmit beamforming to a variable focal point, and receive echoes from single transducer elements that are close-coupled to a 48-channel array of amplifiers. A-line data can then be post processed to perform dynamic receive beamforming. Utilizing this equipment, measurements of pressure field distributions are presented, and compared with simulations, to determine the optimum number of pulsed elements. Using the arrays in pulse-echo mode, imaging quality is assessed with biological tissue samples and ultrasound phantoms. A prototype transducer, operated to produce ultrasound with >20MHz centre frequency, realized spatial resolution of <0.4mm laterally and 0.1mm axially, at a distance of 15mm from the transducer.