Cerebral CT Venography Using a 320-MDCT Scanner With a Time-Density Curve Technique and Low Volume of Contrast Agent: Comparison With Fixed Time-Delay Technique

Image-quality characteristics in the longitudinal direction from different image-reconstruction algorithms during single-rotation volume acquisition on head computed tomography: A phantom study

Background

A multi detector computed tomography (CT) scanner with wide-area coverage enables whole-brain volumetric scanning in a single rotation.

Purpose

To investigate variations in image-quality characteristics in the longitudinal direction for different image-reconstruction algorithms and strengths with phantoms.

Material and methods

Single-rotation volume scans were performed on a 320-row multidetector CT volume scanner using three types of phantoms. Tube current was set to 200 mA (standard dose) and 50 mA (low dose). All images were reconstructed with filtered back projection (FBP), mild and strong levels with hybrid iterative reconstruction (HIR), and model-based IR (MBIR). Computed tomography numbers, image noise, noise power spectrum (NPS), task-based transfer function (TTF), and visual spatial resolution were used to evaluate uniformity of image quality in the longitudinal direction ( Z-axis).

Results

The MBIR images showed smaller variation in CT numbers in the Z-axis. The difference in the highest and lowest CT numbers was smaller (5.0 Hounsfield units [HU]) for MBIR than for FBP (6.6 HU) and HIR (6.8 HU). The variations in image noise were the smallest for strong MBIR and the largest for FBP. The low-frequency component at NPS0.2 was lower for strong MBIR than for other algorithms. The high-frequency component at NPS0.8 was low in all reconstructions. For MBIR, the image resolution and TTFs were higher in the outer portion than in the center.

Conclusion

Model-based IR is the optimal image-reconstruction algorithm for single-volume scan of spherical subjects owing to its high in-plane resolution and uniformity of CT numbers, image noise, and NPS in the Z-axis.

A novel protocol for three-dimensional rotational venography with low-dose contrast media in preoperative angiography of brain tumours

AIM

The most appropriate imaging protocol for three-dimensional rotational venography (3D RV) has not been established. The aim of this study was to optimise the protocol for 3D RV with low-dose contrast media using time-density curve analysis.

METHODS

Twenty-five consecutive patients with brain tumours who received preoperative assessment with 3D RV were retrospectively collected and included in this study. To optimise the imaging delay time of 3D RV with low-dose contrast media, time-density curve analysis was performed on two-dimensional conventional angiography. The image quality for depicting cortical veins and venous sinuses was compared to that of magnetic resonance (MR) venography in five cases.

RESULTS

A total of 27 3D RVs were performed in 25 patients. The time-density curves of cortical veins were different from those of cerebral arteries or sinuses. The mean time to peak of cortical veins was significantly longer than the time to peak of cerebral arteries (2.47 ± 0.35 seconds vs. 6.44 ± 1.14 seconds; p < 0.0001) and shorter than the time to peak of venous sinuses (6.44 ± 1.14 seconds vs. 8.18 ± 1.12 seconds; p < 0.0001). The optimal imaging delay time could be determined as the phases in which cortical arterial opacities disappeared and cortical veins started to appear. The mean dose of injected contrast media was 5.3 mL. The image quality of cortical veins in 3D RV was superior to that in MR venography in all cases.

CONCLUSIONS

Three-dimensional RV with low-dose contrast media was useful for the preoperative assessment of cortical veins in patients with brain tumours.

Investigation of an optimized scanning protocol for the dentomaxillofacial region using 320-slice multidetector computed tomography

OBJECTIVES

To propose an imaging protocol that provides satisfactory image quality for oral examination while minimizing radiation dosage using 320-slice multidetector CT (MDCT).

METHODS

An anthropomorphic head phantom was scanned using 320 MDCT with protocols combining different scanning modes: volume scanning (whole or local) vs helical scanning (80- or 64-slice detectors); tube voltage settings (80 kVp, 120 kVp and 135 kVp); and tube current settings (60 mA, 80 mA, 100 mA and 120 mA). A total of six anatomical bone structures and three anatomical soft-tissue structures were assessed using quantitative and qualitative analysis in the three orthographic planes (axial, sagittal and coronal). A figure of merit (FOM) was used to determine the optimal imaging protocol in terms of tube voltage, tube current and scanning mode.

RESULTS

The 80-kVp setting had the worst quantitative and qualitative results (both p < 0.001) compared with the 135-kVp and 120-kVp settings, especially for soft-tissue structures. A significant difference was noted for the scores obtained using a tube current between 120 mA and 60 mA by quantitative analysis, but not by qualitative analysis. Volume scans using either whole or local modes had a significantly higher FOM than helical scanning of 80 or 64 slices.

CONCLUSIONS

In 320 MDCT, a protocol using 135 kVp, 80 mA and the volume-scanning mode (whole or local) offers adequate visualization of both soft-tissue and bone structures while keeping the radiation dose as low as possible. This may therefore be considered a first choice among a wide selection of scanning protocols for dentomaxillofacial CT.

Radiation Dose Reduction in 4D Cerebral CT Angiography by Individualized Estimation of Cerebral Circulation Time

BACKGROUND AND PURPOSE

The novel technique of 4D CTA for dynamic assessment of the intracranial vessels has a greater radiation burden than conventional CTA. Previous descriptions of the technique used a fixed-duration exposure protocol. This study examines the potential for dose reduction by individualizing exposure time to patient physiology by the use of time-enhancement curve techniques as previously applied in CT angiography and venography.

MATERIALS AND METHODS

4D-CTA examinations performed at our institution were retrospectively reviewed. Scan protocols used a test-bolus scan with either a subjective estimate of the main acquisition timing (estimated-duration method) or a quantitative measure (measured-duration method). The estimated-duration method used peak arterial enhancement to determine the start of exposure, with the duration chosen at the radiologist's discretion. The measured-duration method used arterial and venous time-enhancement curves to determine exposure start and duration. Exposure duration, study adequacy, quality score, and maximum venous enhancement were compared among groups.

RESULTS

One hundred fifty-one examinations used the estimated-duration method, and 53 used measured-duration. The measured-duration method used a shorter exposure time (10 versus 15.8 seconds; P < .001). There was no statistically significant difference in the study adequacy rate, subjective quality score, or maximum venous enhancement. The radiation dose was reduced by 51% in the measured-duration method (3021 mGy × cm, 6.9 mSv, versus 1473 mGy × cm, 3.4 mSv). Both methods showed good agreement with DSA (κ = 0.88 for estimated-duration, κ = 1.0 for measured duration).

CONCLUSIONS

Exposure time in 4D-CTA can be reduced with dual time-enhancement curves to match exposure to physiology without degrading study adequacy or quality.