Subtracted 3D CT angiography for the evaluation of intracranial aneurysms in 256-slice multidetector CT: usefulness of the 80-kVp plus compact contrast medium bolus protocol

Computed Tomography of the Head : A Systematic Review on Acquisition and Reconstruction Techniques to Reduce Radiation Dose

In 1971, the first computed tomography (CT) scan was performed on a patient's brain. Clinical CT systems were introduced in 1974 and dedicated to head imaging only. New technological developments, broader availability, and the clinical success of CT led to a steady growth in examination numbers. Most frequent indications for non-contrast CT (NCCT) of the head include the assessment of ischemia and stroke, intracranial hemorrhage and trauma, while CT angiography (CTA) has become the standard for first-line cerebrovascular evaluation; however, resulting improvements in patient management and clinical outcomes come at the cost of radiation exposure, increasing the risk for secondary morbidity. Therefore, radiation dose optimization should always be part of technical advancements in CT imaging but how can the dose be optimized? What dose reduction can be achieved without compromising diagnostic value, and what is the potential of the upcoming technologies artificial intelligence and photon counting CT? In this article, we look for answers to these questions by reviewing dose reduction techniques with respect to the major clinical indications of NCCT and CTA of the head, including a brief perspective on what to expect from current and future developments in CT technology with respect to radiation dose optimization.

Digital subtraction CT angiography for the detection of posterior inferior cerebellar artery aneurysms: comparison with digital subtraction angiography

OBJECTIVE

To evaluate the diagnostic accuracy of digital subtraction CT angiography (DS-CTA) in detecting posterior inferior cerebellar artery (PICA) aneurysms with digital subtraction angiography (DSA) as reference standard.

METHODS

A total of 115 patients, including 56 patients diagnosed with PICA aneurysms by CTA or DSA and 59 non-PICA-aneurysm patients were included in this retrospective study. All patients underwent DS-CTA and DSA. The site of PICA aneurysms and the pattern of haemorrhage were analysed. Sensitivity and specificity of DS-CTA without and with combining haemorrhage pattern in diagnosing PICA aneurysms were evaluated on a per patient and per aneurysm basis with DSA.

RESULTS

Of 115 patients, 56 patients (48.7%) had 61 PICA aneurysms (size range, 1.1-13.5 mm; mean size, 4.9 ± 2.8 mm) on DSA. The sensitivity and specificity in depicting PICA aneurysms were 89.3% and 96.6% on a per patient basis and 90.2% and 93.4% on a per aneurysm basis, while the corresponding values were 94.6% and 96.6% on a per patient basis and 95.1% and 93.4% on a per aneurysm basis when combining with haemorrhage site.

CONCLUSION

DS-CTA has a high sensitivity and specificity in detecting PICA aneurysms compared with DSA. It may be helpful for clinical diagnosis of PICA aneurysms to combine with haemorrhage sites.

KEY POINTS

• CT angiography has a good diagnostic performance in detecting PICA aneurysms. • The haemorrhage location is helpful to detect PICA aneurysms. • Digital subtraction CTA is a preferable diagnostic means for PICA aneurysms.

Evaluation of image quality in carotid and cerebrovascular disease: a comparative study between subtraction and routine computed tomography angiography

OBJECTIVE

Few data exist comparing the image quality and diagnostic accuracy of subtraction computed tomography (CT) angiography (SCTA) in carotid and cerebrovascular arteries with routine CT angiography (RCTA).

PATIENTS AND METHODS

In this study, 56 patients underwent 128-row CT angiography of these vessels with review by two radiologists using routine, nonsubtracted, and SCTA protocols. Comparisons were made using a 4-point subjective rating scale in all patients. Eighteen patients were examined with both SCTA and invasive digital subtraction angiography (DSA). The accuracy of SCTA and routine CTA reformations was assessed and compared by both patient-based and vessel-based analyses of intracranial aneurysms and intracranial and extracranial arterial stenotic lesions using DSA results as the reference standard.

RESULTS

Diagnostic accuracy in the adjacent skull base portion of the internal carotid artery (ICA) and reading time for cerebral aneurysms and vessel stenoses were obviously improved with SCTA protocol, but the accuracy in vertebro-basilar arteries was no different. The diagnostic accuracy in general was slightly increased compared with routine CTA.

CONCLUSION

Review of SCTA images is an effective means to remove bone close to vessels as seen on routine CTA and has good image quality and diagnostic accuracy. SCTA is superior to routine CTA in the visualization and diagnostic accuracy of adjacent skull base part of the ICA and decreases reading time for carotid and cerebrovascular arterial imaging.

Effects of a high-pitch protocol and a hybrid iterative reconstruction algorithm on image quality of cerebral subtracted 3D CT angiography

PURPOSE

To evaluate the image quality and the radiation dose of 3D-computed tomography angiography (3D-CTA) with a high-pitch protocol and a hybrid iterative reconstruction (HIR).

MATERIALS AND METHODS

This was a prospective study and thirty patients were scanned at a 0.51-helical pitch with filtered back-projection (FBP, protocol-A), and 30 patients were scanned at a 0.91-helical pitch with FBP and HIR (protocol-B and C). The mean volume CT dose index (CTDI(vol)), image noise, and mean cerebral arterial and venous attenuation were compared between the three protocols. Two readers assessed image noise, arterial contrast and venous overlap.

RESULTS

The mean CTDI(vol) of protocol-B/C (38.9 mGy) was lower than that of protocol-A (49.7 mGy). Mean image noise of protocol-B [12.6 ± 1.3 Hounsfield units (HU)] was higher than that of protocol-A (10.3 ± 1.2 HU). There was no significant difference in arterial attenuation between protocol-A (327.5 ± 57.5 HU) and C (327.7 ± 59.4 HU). Venous attenuation of protocol-C (148.5 ± 50.4 HU) was lower than that of protocol-A (185.9 ± 50.6 HU). In qualitative analysis, the image noise of protocol-B was higher than that of protocol-A/C. Venous enhancement of protocol-B/C was more inconspicuous than that of protocol-A.

CONCLUSIONS

3D-CTA with a high-pitch protocol and HIR can reduce radiation dose while decreasing venous enhancement and image noise to an adequate level for diagnosis.

The value of cerebral CT angiography with low tube voltage in detection of intracranial aneurysms

Objective. The aim of this study is to investigate the value of cerebral CT angiography (CTA) with low tube voltage in detection of intracranial aneurysms. Materials and Methods. A total of 294 consecutive patients with spontaneous subarachnoid hemorrhage (SAH) were enrolled in this study and randomly assigned into conventional voltage CTA (C-CTA) group and low voltage CTA (L-CTA) group. The objective and subjective image qualities were analyzed and compared between C-CTA and L-CTA groups. With the results of 3D-DSA as “gold standard,” the sensitivity, specificity, and accuracy of C-CTA and L-CTA in diagnosis of aneurysms were calculated and compared with each other. Results. Compared with group C-CTA, the CT dose index volume (CTDIvol) of group L-CTA reduced by 35.65%. There were no significant differences between C-CTA and L-CTA groups regarding objective and subjective image qualities. The sensitivity, specificity, and accuracy of L-CTA in diagnosis of aneurysms were 95.16%, 99.72%, and 99.42%, respectively. There were no significant differences in sensitivity, specificity, and accuracy between the C-CTA and L-CTA groups. Conclusion. The value of cerebral CTA with 100 kV low tube voltage in detection of intracranial aneurysms is significant, and it should be recommended as a routine scan method.