High-pitch dual-source CT angiography of supra-aortic arteries: assessment of image quality and radiation dose

INTRODUCTION

High-pitch CT angiography (CTA) is a recent innovation that allows significant shortening of scan time with volume coverage of 43 mm per second. The aim of our study was to assess this technique in CTA of the head and neck.

METHODS

CTA of supra-aortic arteries was performed in 50 patients using two acquisition protocols: conventional single-source 64-slice (pitch 1.2) and high-pitch dual-source 128-slice CT (pitch 3.2). Subjective and objective image quality of supra-aortic vessel ostia as well as intra- and extra-cranial segments was retrospectively assessed by blinded readers and radiation dose compared between the two protocols.

RESULTS

Conventional and high-pitch CTA achieved comparable signal-to-noise ratios in arterial (54.3 ± 16.5 versus 57.3 ± 14.8; p = 0.50) and venous segments (15.8 ± 6.7 versus 18.9 ± 8.9; p = 0.21). High-pitch scanning was, however, associated with sharper delineation of vessel contours and image quality significantly improved at the level of supra-aortic vessel ostia (p < 0.0001) as well as along the brachiocephalic trunk (p < 0.0001), the subclavian arteries (p < 0.0001), proximal common carotid arteries (p = 0.01), and vertebral V1 segments (p < 0.0001). Using the high-pitch mode, the dose-length product was reduced by about 35% (218.2 ± 30 versus 141.8 ± 20 mGy × cm).

CONCLUSIONS

Due to elimination of transmitted cardiac motion, high-pitch CTA of the neck improves image quality in the proximity of the aortic arch while significantly lowering radiation dose. The technique thus qualifies as a promising alternative to conventional spiral CTA and may be particularly useful for identification of ostial stenosis.

Developing standards of care for HIV prevention research in developing countries -- a case study of 10 research centers in Eastern and Southern Africa

Standards of care provided to volunteers in HIV prevention research in developing countries are evolving. Inconsistency in standards, particularly within a research network highlights the need to balance volunteers' health and wellness with the efficient conduct of research. Ten research centers (RC's) in East and Southern Africa affiliated with the International AIDS Vaccine Initiative (IAVI) were studied using a mixed methods approach to understand variations, similarities and gaps in services provided, recipients of services, referral systems, and barriers to referral uptake. These data were then used to develop expected standards across the 10 RCs. Findings indicated that RCs consistently provided HIV risk reduction and family planning (FP) counseling, male condoms, management of sexually transmitted infections, CD-4 counts, and general medical care to volunteers and non-research volunteers. Services that were less consistently provided on-site included: female condoms, adult male circumcision (AMC), antiretroviral therapy (ART) and post-exposure prophylaxis (PEP) in case of rape. The FP options provided on-site varied, with few providing implants, intrauterine devices, tubal ligation, and vasectomy. Most RCs had established referral systems for ART, AMC, PEP, and FP, but few had referral points for psychosocial services. Few RCs had comprehensive guidelines on referrals other than those related to adverse events. Findings indicate that the greatest challenges for referral uptake were transportation and health care costs, poor quality and inconsistency of services at some referral points. Few RCs covered the cost of referrals for non-study related adverse events. A collaborative process between IAVI and the RCs was undertaken to reach consensus on expected standards of care. A set of required and recommended services to be provided on-site or by referral was developed. In developing such standards, we tried to balance scientific priorities, equity, contextual realities, community expectations, and cost-effectiveness.

Iterative reconstruction in head CT: image quality of routine and low-dose protocols in comparison with standard filtered back-projection

BACKGROUND AND PURPOSE

IR has recently demonstrated its capacity to reduce noise and permit dose reduction in abdominal and thoracic CT applications. The purpose of our study was to assess the potential benefit of IR in head CT by comparing objective and subjective image quality with standard FBP at various dose levels.

MATERIALS AND METHODS

Ninety consecutive patients were randomly assigned to undergo nonenhanced and contrast-enhanced head CT at a standard dose (320 mAs; CTDI, 60.1) or 15% (275 mAs; CTDI, 51.8) and 30% (225 mAs; CTDI, 42.3) dose reduction. All acquisitions were reconstructed with IR in image space, and FBP and images were assessed in terms of quantitative and qualitative IQ.

RESULTS

Compared with FBP, IR resulted in lower image noise (P ≤ .02), higher CNR (P ≤ .03), and improved subjective image quality (P ≤ .002) at all dose levels. While degradation of objective and subjective IQ at 15% dose reduction was fully compensated by IR (CNR, 1.98 ± 0.4 at 320 mAs with FBP versus 2.05 ± 0.4 at 275 mAs with IR; IQ, 1.8 versus 1.7), IQ was considerably poorer at 70% standard dose despite using the iterative approach (CNR, 1.98 ± 0.3 at 320 mAs with FBP versus 1.85 ± 0.4 at 225 mAs with IR, P = .18; IQ, 1.8 versus 2.2, P = .03). Linear regression analysis of CNR against tube current suggests that standard CNR may be obtained until approximately 20.4% dose reduction when IR is used.

CONCLUSIONS

Compared with conventional FBP, IR of head CT is associated with significant improvement of objective and subjective IQ and may allow dose reductions in the range of 20% without compromising standard image quality.

Optimized 3D magnetization-prepared rapid acquisition of gradient echo: identification of thalamus substructures at 3T

BACKGROUND AND PURPOSE

Because the substructures of the thalamus are not visible on standard T1- and T2-weighted MR images, planning of deep brain stimulation implantation relies on stereotactic atlas coordinates. The goal of the present work was to test whether an optimized 3D MPRAGE protocol can depict thalamus substructures.

MATERIALS AND METHODS

After optimization of the TI to maximize contrast between gray matter and white matter, 6 healthy subjects were scanned at 3T with the optimized 3D MPRAGE. The results were compared with stereotactic atlases, and 2 expert readers trained in thalamic anatomy identified the 4 large thalamic nuclei groups.

RESULTS

There was a high agreement between the different atlases and the resulting MR images. The 4 large thalamic nuclei groups (anterior, lateral, medial, posterior) could be detected reliably. The inter-reader consistency on the size and location was 75%-92%.

CONCLUSIONS

The optimized 3D MPRAGE protocol improves contrast in the thalamus, and the 4 large thalamic nuclei groups can be identified with high inter-reader agreement.

Isometric non-machine-based prevention training program: effects on the cross-sectional area of the paravertebral muscles on magnetic resonance imaging

PURPOSE

The purpose of this study was to determine potential effects of isometric non-machine-based training on the cross-sectional area (CSA) of the paravertebral muscles in volunteers who were participants in a prevention program. An increase in the CSA of back muscles after various machine-based exercises have been reported but non-machine-based training programs have not been adressed before.

MATERIALS AND METHODS

In the study 14 volunteers, who were participants of a company internal prevention program, underwent a magnetic resonance (MR) examination before and after a 3 months training program to improve back muscle strength. The MRI protocol consisted of T1-weighted and T2-weighted images aligned to the intervertebral disc spaces. The CSAs of the erector spinae and quadratus lumborum muscles were assessed twice by 2 operators at the levels L3/4, L4/5 and L5/S1.

RESULTS

Out of 14 subjects 11 completed the training. The recorded CSA values exhibited an intrarater and intrarater correlation coefficient ranging from 0.949 to 0.989. There was an increase in CSA in all subjects after the training period (mean increase 8%).

CONCLUSIONS

A 3-month isometric training program is sufficient to effect measurable increases in back muscles volume. The study demonstrated the usefulness of MRI to quantify such changes as a measure of training efficacy and compliance into the training program. These results represent a rationale for further studies to determine the effect of different training methods on the CSA of back muscles and to correlate structural changes with clinical symptoms in chronic low back pain syndrome.

The in vivo influence of white matter fiber orientation towards B(0) on T2* in the human brain

It is well known that, at higher field strength, T2*-weighted images show an extensive heterogeneity in white matter fiber bundles. The basis of this phenomenon is still under discussion, as many factors, such as iron concentration, myelination and tissue microstructure, could influence relaxation times. Furthermore, fiber direction in relation to the main magnetic field seems to influence T2* relaxation times. In this study, diffusion tensor imaging and T2* measurements were combined in seven subjects with the head in a normal and tilted position. It was shown that fiber orientation has a strong influence on T2* in the human brain, with the average T2* value changing from 49 ms for a perpendicular orientation to B(0) to 57 ms for a parallel orientation to B(0). Nevertheless, T2* times showed a wide variety of values at any orientation towards B(0).

Ensuring quality of services in HIV prevention research settings: findings from a multi-center quality improvement pilot in East Africa

Quality improvement (QI) has been widely implemented in health services but has not been widely applied in HIV prevention research. Most prevention research centers have commonly employed traditional approaches (e.g., checklists) to quality control that document what has been done but not the quality of what has been done. Unlike other health settings, prevention research settings have unique characteristics and ethical requirements that require the development or adaptation of specific quality indicators. A QI model for health services was adapted for use in prevention research settings and was piloted between August 2006 and July 2007 at three research centers in East Africa. Four hundred and twenty-six volunteers exit interviews were administered in two cycles. Quantitative and qualitative data were analyzed using Excel worksheets. QI meeting reports and QI plans were used to complement data from exit interviews. On average, 52% of total enrolled volunteers participated in the exit interview. The designed QI plans successfully helped reduce volunteers' reported waiting time to see counselors (p<0.001) and pharmacists (p<0.001). It also increased the percentage of interviewed volunteers who reported being counseled on family planning at clinical trials (from 66 to 93%; p=0.02) at follow-up visits, and who were refreshed on informed consent at follow-up visits (from 90 to 96%; p=0.009). The percentage of interviewed volunteers that expressed satisfaction with services received from counselors increased (from 87 to 94%; p=0.009) while the percentage of volunteer satisfied with services from trial physicians remained constant (93%). The majority of volunteers interviewed reported satisfaction with other major components of research such as confidentiality, understanding of trial objectives, benefits and risks of participation, and risk reduction counseling. However, satisfaction with services from community outreach workers and other staff at research centers dropped over the course of the study (from 88% in Cycle 1 to 74% in Cycle 3; p= < 0.001). Increased commitment to QI is crucial in ensuring quality of services and ethical conduct of HIV prevention research centers.