Temporal resolution measurement of 128-slice dual source and 320-row area detector computed tomography scanners in helical acquisition mode using the impulse method

Assessment of temporal resolution and detectability of moving objects in CT: A task-based image quality study

The metrics used for assessing image quality in computed tomography (CT) do not integrate the influence of temporal resolution. A shortcoming in the assessment of image quality for imaging protocols where motion blur can therefore occur. We developed a method to calculate the temporal resolution of standard CT protocols and introduced a specific spatiotemporal formulation of the non-prewhitening with eye filter (NPWE) model observer to assess the detectability of moving objects as a function of their speed. We scanned a cubic water phantom with a plexiglass cylindrical insert (120 HU) using a large panel of acquisition parameters (rotation times, pitch factors and collimation widths) on two systems (GE Revolution Apex and Siemens SOMATOM Force) to determine the in-plane task-based transfer functions (TTF) and noise power spectra (NPS). The phantom set in a uniform rectilinear motion in the transverse plane allowed the temporal modulation transfer function (MTF) calculation. The temporal MTF appropriately compared the temporal resolution of the various acquisition protocols. The longitudinal TTF was measured using a thin tungsten wire. The detectability index showed the advantage of applying high rotation speed, wide collimations and high pitch for object detection in the presence of motion. No counterpart to the increase in these three parameters was found in the in-plane and longitudinal image quality.

Updates on Computed Tomography Imaging in Aortic Aneurysms and Dissection

Computed tomography (CT) is a primary imaging modality for the diagnosis of aortic diseases, because of its minimal invasiveness and agility.

Prompt and accurate diagnosis is crucial especially for acute aortic diseases, and the guidelines for acute aortic dissection recommend the use of CT for initial diagnosis. For the follow-up observation of longstanding aortic diseases, the strategy of imaging management by CT must be different from that for emergency and acute phases.

In this review, we document the differences in characteristics and clinical course between aortic aneurysm and aortic dissection and explain the use of recent CT techniques in diagnosing short- and longstanding aortic diseases.

Subjective and objective comparisons of image quality between ultra-high-resolution CT and conventional area detector CT in phantoms and cadaveric human lungs

Objectives

To compare the image quality of the lungs between ultra-high-resolution CT (U-HRCT) and conventional area detector CT (AD-CT) images.

Methods

Image data of slit phantoms (0.35, 0.30, and 0.15 mm) and 11 cadaveric human lungs were acquired by both U-HRCT and AD-CT devices. U-HRCT images were obtained with three acquisition modes: normal mode (U-HRCT_N: 896 channels, 0.5 mm × 80 rows; 512 matrix), super-high-resolution mode (U-HRCT_SHR: 1792 channels, 0.25 mm × 160 rows; 1024 matrix), and volume mode (U-HRCT_SHR-VOL: non-helical acquisition with U-HRCT_SHR). AD-CT images were obtained with the same conditions as U-HRCT_N. Three independent observers scored normal anatomical structures (vessels and bronchi), abnormal CT findings (faint nodules, solid nodules, ground-glass opacity, consolidation, emphysema, interlobular septal thickening, intralobular reticular opacities, bronchovascular bundle thickening, bronchiectasis, and honeycombing), noise, artifacts, and overall image quality on a 3-point scale (1 = worst, 2 = equal, 3 = best) compared with U-HRCT_N. Noise values were calculated quantitatively.

Results

U-HRCT could depict a 0.15-mm slit. Both U-HRCT_SHR and U-HRCT_SHR-VOL significantly improved visualization of normal anatomical structures and abnormal CT findings, except for intralobular reticular opacities and reduced artifacts, compared with AD-CT (p < 0.014). Visually, U-HRCT_SHR-VOL has less noise than U-HRCT_SHR and AD-CT (p < 0.00001). Quantitative noise values were significantly higher in the following order: U-HRCT_SHR (mean, 30.41), U-HRCT_SHR-VOL (26.84), AD-CT (16.03), and U-HRCT_N (15.14) (p < 0.0001). U-HRCT_SHR and U-HRCT_SHR-VOL resulted in significantly higher overall image quality than AD-CT and were almost equal to U-HRCT_N (p < 0.0001).

Conclusions

Both U-HRCT_SHR and U-HRCT_SHR-VOL can provide higher image quality than AD-CT, while U-HRCT_SHR-VOL was less noisy than U-HRCT_SHR.

Key Points

• Ultra-high-resolution CT (U-HRCT) can improve spatial resolution.

• U-HRCT can reduce streak and dark band artifacts.

• U-HRCT can provide higher image quality than conventional area detector CT.

• In U-HRCT, the volume mode is less noisy than the super-high-resolution mode.

• U-HRCT may provide more detailed information about the lung anatomy and pathology.

Electronic supplementary material

The online version of this article (10.1007/s00330-018-5491-2) contains supplementary material, which is available to authorized users.

Characteristics of temporal resolution in 16- and 64-row computed tomography scanners

This study aimed to analyze the temporal sensitivity profile (TSP) shapes and temporal resolutions of computed tomography (CT) and investigate the effect of a combination of a given rotation time and helical pitch on the TSP and image quality. The study was performed on 16- and 64-row CT scanners, and the TSP and temporal resolution were measured using the impulse method. A shorter gantry rotation time and larger helical pitch improved the temporal resolution of both CT scanners. Although the measured TSP shapes were dependent on the helical pitch, the maximum helical pitch did not improve the temporal resolution of either CT scanner. Different combinations of gantry rotation time and helical pitch yielded different TSP shapes such as the triangle, trapezoid, and rectangle, despite the use of equivalent scan speeds. We suggest that the different combinations of rotation time and helical pitch can greatly affect the TSP shapes.