Task-based selection of three-dimensional rotational angiography imaging modes using in-house phantom.

INTRODUCTION: The presence of two modes of three-dimensional rotational angiography (3DRA), both intended for cranial applications with similar protocol names ('cerebral' and 'head limited' with no explanation on what the phrase 'limited' represent), had caused some degree of difficulty with the clinicians and radiographers on deciding which mode to select for which task. This study was aimed to use an in-house phantom to assist with this clinical issue of 3DRA usage in terms of mode selection. METHODS: An in-house phantom was used in this study to further analyze and recommend selection. A variety of iodinated contrast agent (ICA) concentrations in the objects were used to simulate clinical images of cranial vessels. The Kerma-area product (KAP) was used as dose metric, while the signal difference to noise ratio (SDNR) of the artificial vessels was employed to represent image quality in terms of contrast. The x-ray spectrum analysis was performed for quantitative evaluation. RESULTS: The non-standard 'head limited' mode is more suggestible for use. Additionally, the 'low' detail option provides the lowest KAP (due to low tube loading) but provided slightly higher SDNR compared to those from 'normal' detail option. A minimum concentration of 18.5 mg/ml of iodine is required to obtain the comparable SDNR with those of higher concentration when the 'low' detail option is selected. CONCLUSION: The 'head limited' mode with 'low' detail options is advisable for contrast-enhanced procedures. To ensure proper use of each mode, effective collaboration should be established between clinical users, medical physicists, and manufacturer's technical representatives. IMPLICATIONS FOR PRACTICE: Selection modes for 3DRA procedures have been made less subjective, following dose and image quality of each mode. Future issues can be addressed by collaborating with medical physicists.

Novel phantom for performance evaluation of contrast-enhanced 3D rotational angiography.

PURPOSE: This technical note presents an in-house phantom with a specially designed contrast-object module constructed to address the need for three-dimensional rotational angiography (3DRA) testing. METHODS: The initial part of the study was a brief evaluation on the commercially available phantom used for 3DRA and computed tomography angiography (CTA) to confirm the need for a special phantom for 3D angiography. Once confirmed, an in-house phantom was constructed. The novel phantom was tested to evaluate the basic image performance metrics, i.e., unsharpness (MTF) and noise characterization (NPS), as well as to show its capability for vessel contrast visibility study. RESULTS: The low contrast objects in the commercially available tools dedicated for CT is found to yield significantly lower signal difference to noise ratio (SDNR) when used for 3DRA, therefore deemed inadequate for 3DRA contrast evaluation. The constructed in-house phantom demonstrates a capability to serve for basic imaging performance check (MTF, NPS, and low contrast evaluation) for 3DRA and CTA. With higher and potentially adjustable visibility of contrast objects as artificial vessels, the in-house phantom also makes more clinically relevant tests, e.g., human- or model observer study and task-based optimization, possible. CONCLUSION: The novel phantom with special contrast object module shows higher visibility in 3DRA compared to the currently available commercial phantom and, therefore, is recommended for use in 3D angiography.