Objective: To identify the optimal monoenergetic level, balancing metal artefacts, and the amount of noise present for imaging of metal implants using dual-energy computed tomography (CT) and focusing on the assessment of peri-prosthetic soft tissue. Methods: Four metallic implants commonly used in the hips were placed in a phantom body: unipolar hemiprosthesis, dynamic hip screw (DHS), intra-medullary (IM) nail, and titanium insert. The unipolar hemiprosthesis was imaged at two points: the head and stem. The head of the hemiprosthesis and DHS were imaged in two axes: one axial to and one resembling the angle at its expected position in the hip with respect to the scanner. The IM nail was assessed both at the level with and without a screw inserted. A region of interest to measure the noise level of the images was first performed with different monoenergetic levels (70-170 kV with increments of 10 kV). Four monoenergetic levels were then chosen (80, 90, 105, 120 kV) for each implant and were assessed and scored (presence of least to most artefacts: score 1-4) by nine radiologists who were blinded to the monoenergetic level. A total of eight sets of images were assessed. The scores for different monoenergetic levels were compared using analysis of variance. Results: In the first part of the experiment, the images with the least amount of noise were in the range of 85-95 kV, thus we included 90 kV among the images for subsequent scoring. The mean score for different monoenergetic levels for all implants was as follows: 3.94 for 80 kV, 2.68 for 90 kV, 1.50 for 105 kV, and 1.88 for 120 kV (p <0.001), with 105 kV having the least metal artefacts. For subgroup analysis of individual implants, 105 kV was found to produce the best quality images with a statistically significant better score for hip stem, DHS, and IM nail. 120 kV trended towards being the best monoenergetic level when imaging the hip head and the IM nail with screw where relatively more artefacts were present. 90 kV trended towards being the best monoenergetic level when imaging the titanium insert where artefacts were nearly absent. Conclusion: With regard to imaging the soft tissue around a metallic implant, the overall optimal monoenergetic level for reduction of metal artefacts using dual-energy CT is 105 kV. When more artefacts are inherently present, 120 kV trended towards being the best monoenergetic level. When artefacts are minimal, 90 kV trended towards being the optimal monoenergetic level with the least amount of noise present.

Perivascular epithelioid cell tumour is a relatively new entity with rising incidence. This is a rare mesenchymal neoplasm that can occur in various organs and is characterised by proliferation of perivascular cells and expression of myomelanocytic markers. Here, we present an asymptomatic 52-year-old female patient with an incidental radiological finding of a large retroperitoneal mass, histologically and immunohistochemically proven to be a sclerosing type of perivascular epithelioid cell tumour. The mass showed typical morphological and microscopic features consistent with those described in the current literature. However, it had computed tomography findings of neovascularisation and hyper-vascularity, not often documented in previous case reports of the sclerosing type of tumours. Literature review, using PubMed, of intraperitoneal / retroperitoneal type of tumours, and specifically the sclerosing type, was performed. To the best of our knowledge, less than 20 sclerosing perivascular epithelioid cell tumours have been reported and few describe the associated radiological features.

Objective: Stereotactic-guided vacuum-assisted biopsy (VAB) can be performed in small breast masses, distortions, and microcalcifications. A metallic marker is deployed at the corresponding biopsy site to facilitate localisation if additional surgery is required. There is currently limited literature on the accuracy of marker placement in Asian breasts that tend to be smaller and denser than those in Caucasians. The objective of this study was to evaluate the factors that may affect marker migration in stereotactic VAB at a regional hospital in Hong Kong. Methods: From January 2010 to June 2015, all stereotactic VAB performed in the screening population at Kwong Wah Hospital were reviewed through the Hologic Selenia workstations and electronic patient records. Consensus between the local breast surgeons and radiologists defined marker migration of <1 cm as insignificant displacement. Marker migration of >1 cm could affect surgical localisation. Factors including age, indication, Breast Imaging-Reporting and Data System (BIRADS) category, needle approach, breast density, breast compression thickness, depth of the lesion, number of biopsy cuttings, complications, and duration of the procedure were recorded. The distance of marker migration from the biopsy site in cranio-caudal and mediallateral oblique views was measured. Results: A total of 154 Asian patients underwent stereotactic VAB during the study period. One patient was excluded due to technical failure during deployment of the marker. Of the remaining 153 patients, there was migration of 45 (29.4%) markers, of which 19 (12.4%) were <1 cm, 16 (10.5%) 1-3 cm, 7 (4.6%) 3-5 cm, and 3 (2.0%) >5 cm. Factors including older age, thicker breasts, greater number of biopsy cuttings, and longer duration of the procedure showed statistical significance in affecting marker migration (p < 0.05). Conclusion: This study identified four factors that could influence marker migration, namely age, breast compression thickness, number of biopsy cuttings, and duration of procedure. Awareness of these factors during the planning of the procedure could potentially decrease the effect of marker migration and thus enable more accurate surgical localisation.

Objective: To evaluate the characteristics and clinical outcome of non-palpable breast lesions screened by ultrasound. Methods: From January 2011 to June 2011, all new cases referred to the breast clinic at Tuen Mun Hospital, Hong Kong, were identified. All patients underwent ultrasound with or without mammography. Patients with a palpable or mammographically detected breast mass were included in the control group. Patients with nonpalpable breast lesions detected incidentally on ultrasound only were included in the investigation group. Any patients who underwent targeted ultrasound were excluded. Baseline patient demographics, including age and family history of breast cancer, were documented. Lesion characteristics on ultrasound, including maximum dimension and Breast Imaging Reporting and Data System (BI-RADS) classification, were analysed. The nature of the lesions was confirmed histologically or by follow-up imaging for at least 2 years to indicate benignity. Results: A total of 196 patients with 422 lesions were identified. Among the 422 lesions, 130 were palpable or mammographically detected lesions (control group) and 292 were non-palpable ultrasound-detected lesions (investigation group). The baseline characteristics in both groups were comparable. The mean age was 44 years in the control group and 42 years in the investigation group. There were 10 and 8 patients with a family history of breast cancer in the control group and investigation group, respectively. Compared with the control group, the maximum dimension of the lesion was significantly smaller in the investigation group (p < 0.05). The BI-RADS classification was significantly lower in the investigation group (p < 0.05). A total of 156 lesions had tissue diagnosis and 270 lesions were followed up for at least 2 years with no change or a decrease in size, indicating benignity. In the control group, 18 (13.8%) lesions were malignant while in the investigation group, no lesions were malignant (p < 0.05). Conclusion: Ultrasound can detect small lesions that are mammographically occult and non-palpable. However, these lesions are likely more benign-looking (BI-RADS 2/3) and pathologically benign.

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