Evaluation of ECG-Gated, High-Pitch Thoracoabdominal Angiographies With Dual-Source Photon-Counting Detector Computed Tomography

PURPOSE

The aim of this study was to evaluate the radiation dose, image quality, and the potential of virtual monoenergetic imaging (VMI) reconstructions of high-pitch computed tomography angiography (CTA) of the thoracoabdominal aorta on a dual-source photon-counting detector-CT (PCD-CT) in comparison with an energy-integrating detector-CT (EID-CT), with a special focus on low-contrast attenuation.

METHODS

Consecutive patients being referred for an electrocardiogram (ECG)-gated, high-pitch CTA of the thoracoabdominal aorta prior to transcatheter aortic valve replacement (TAVR), and examined on the PCD-CT, were included in this prospective single-center study. For comparison, a retrospective patient group with ECG-gated, high-pitch CTA examinations of the thoracoabdominal aorta on EID-CT with a comparable scan protocol was matched for gender, body mass index, height, and age. Virtual monoenergetic imaging reconstructions from 40 to 120 keV were performed. Enhancement and noise were measured in 7 vascular segments and the surrounding air as mean and standard deviation of CT values. The radiation dose was noted and signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. Finally, a subgroup analysis was performed, comparing VMI reconstructions from 40 keV to 70 keV in patients with at least a 50% decrease in contrast attenuation between the ascending aorta and femoral arteries.

RESULTS

Fifty patients (mean age 77.0±14.5 years; 31 women) were included. The radiation dose was significantly lower on the PCD-CT (4.2±1.4 vs. 7.2±2.2 mGy; p<0.001). With increasing keV, vascular noise, SNR, and CNR decreased. Intravascular attenuation was significantly higher on VMI at levels from 40 to 65, compared with levels of 120 keV (p<0.01 and p<0.005, respectively). On the PCD-CT, SNR was significantly higher in keV levels 40 and 70 (all p<0.001), and CNR was higher at keV levels 40 and 45 (each p<0.001), compared with scans on the EID-CT. At VMI ≤60 keV, image noise was also significantly higher than that in the control group. The subgroup analysis showed a drastically improved diagnostic performance of the low-keV images in patients with low-contrast attenuation.

CONCLUSION

The ECG-gated CTA of the thoracoabdominal aorta in high-pitch mode on PCD-CT have significantly lower radiation dose and higher objective image quality than EID-CT. In addition, low-keV VMI can salvage suboptimal contrast studies, further reducing radiation dose by eliminating the need for repeat scans.

CLINICAL IMPACT

ECG-gated CT-angiographies of the thoracoabdominal aorta can be acquired with a lower radtiation dose and a better image quality by using a dual-source photon-countinge detector CT. Furthermore, the inherent spectral data offers the possiblity to improve undiagnostic images and thus saves the patient from further radiation and contrast application.

Evaluation of run-off computed tomography angiography on a first-generation photon-counting detector CT scanner - Comparison with low-kVp energy-integrating CT

PURPOSE

To assess the overall imaging performance (radiation dose and image quality) of a photon-counting detector CT (PCD-CT) in comparison with a state-of-the-art energy-integrating detector CT (EID-CT) in run-off CTAs.

METHODS

Consecutive patients who underwent run-off CTA on a PCD-CT were included (PCD-CT cohort). A retrospective cohort of patients who had undergone run-off CTA on an EID-CT was matched for gender, body mass index, height, and age (EID-CT cohort). Virtual monoenergetic imaging (VMI) reconstructions for various keV settings (40-120 keV) were generated. CT values and noise were semiautomatically measured for 13 vascular segments of the abdomen, pelvis, and lower extremities. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated for each segment. Subjective image quality was evaluated by two radiologists along the dimensions 'vessel attenuation', 'vessel sharpness', and 'overall image quality' using 5-point Likert scales.

RESULTS

Forty patients (age 70.9 ± 9.8 years; 14 women) were included in the PCD-CT cohort and matched with a corresponding number of EID-CT patients. Overall, there was an inverse correlation of signal and noise but also of SNR and CNR with keV levels used for VMI reconstructions. SNR and CNR in the 40 - 60 keV range exceeded EID-CT levels significantly. Subjective image quality was substantially higher at lower keV levels and showed no significant difference to EID-CT.

CONCLUSION

Low keV VMI reconstructions of run-off CTA scans on a PCD-CT result in substantially higher SNR and CNR than 80 kVp and 100 kVp EID-CT acquisitions with equal subjective image quality.

Optimizing dynamic range in children using the nucleus cochlear implant

OBJECTIVE

The aim of this study was to investigate the benefits of the preprocessing scheme "Adaptive Dynamic Range Optimization" (ADRO) in children using Nucleus cochlear implants. Previous research with adults indicates improved speech perception in quiet and improved sound quality in everyday listening environments with the ADRO scheme.

DESIGN

Children were given 4 wk of take-home experience with ADRO, with a minimum of 2 wk in which ADRO was "locked-in." After 1 wk of ADRO use and again after 4 wk of ADRO use, Bench-Kowal-Bamford (BKB) sentence perception in quiet at a low input level of 50 dB SPL (unweighted root mean square) and sentence perception in noise were compared with the child's everyday (Standard) program and the ADRO program. Children also rated the loudness of a variety of environmental sounds and indicated which program provided the best hearing in a variety of everyday listening situations.

RESULTS

On average, BKB sentence perception in quiet at 50 dB SPL was significantly better with the ADRO program compared with the Standard program. The group mean improvement was 8.60%. Similarly, group mean scores for BKB sentences presented at 65 dB SPL in multitalker babble were significantly higher with the ADRO program (an improvement of 6.87%). The ADRO program was the preferred program in 46% of the listening situations, whereas the Standard program was preferred in 26% of situations. Everyday sounds were not unacceptably loud with ADRO.

CONCLUSIONS

There was an ADRO benefit for this group of children in quiet and in noise. These findings suggest that young children would benefit from the ADRO programming option being locked in along with other processor settings in the SPrint processor once their MAP levels have stabilized. Some older children and teenagers may choose to use ADRO selectively for specific listening situations.

Conversion from the SPEAK to the ACE strategy in children using the nucleus 24 cochlear implant system: speech perception and speech production outcomes

OBJECTIVE

The main objective of this study was to assess whether speech perception and speech production in children using the Nucleus 24 cochlear implant system improved with a change in speech processing strategy from the SPEAK to the Advanced Combination Encoder (ACE) strategy. The major difference between the two strategies is that ACE uses a higher stimulation rate (in this study the stimulation rate was 900 Hz per channel) compared with the SPEAK strategy, where the stimulation rate is 250 Hz per channel. Information also was obtained regarding the adjustment period after conversion to the ACE strategy.

DESIGN

An ABA experimental design was used where scores were initially obtained using the SPEAK strategy' (in the initial A time interval), and subsequently performance was assessed using the ACE strategy (B time interval) and then again with the SPEAK strategy (second A time interval). The duration of the B interval was 10 wk, and the duration for the second A interval was 4 wk. Seven children aged between 9 and 16 yr who had at least 6 mo experience with the SPEAK strategy participated. Open-set monosyllabic CNC word perception in quiet and Speech Intelligibility Test sentence perception in noise was evaluated at the end of each of the time intervals. Word perception was also monitored at fortnightly intervals during the B time interval. Speech production was assessed at the end of the initial A time interval and at the end of the B time interval.

RESULTS

Mean word and phoneme scores for open-set words in quiet for the group of seven children were significantly higher with the ACE strategy as compared with the SPEAK strategy scores obtained in both of the A time intervals. For sentences in noise, mean scores using the ACE strategy as well as the SPEAK strategy at the second A evaluation point were significantly higher than the scores using the SPEAK strategy measured at the first A time interval. This suggests that learning effects may have influenced outcomes. For some subjects, an initial decrease in scores was found during the initial 2-wk period after fitting the ACE strategy; however, scores subsequently were found to be similar to or higher than those when using the initial SPEAK strategy. Analysis of speech production assessments showed an improvement in the medial consonant scores after using the ACE strategy.

CONCLUSIONS

This study demonstrated that some children were able to benefit from the additional information provided by the ACE strategy as compared with the SPEAK strategy. However, the differences in overall performance between the two strategies appear to be relatively small.

Exposures to lead-based paint dust in an inner-city high school

In response to concerns about lead-based paint (LBP) in an 85-year old high school, an evaluation was conducted to determine whether a lead exposure hazard existed for adult school staff. Deteriorating LBP was present on walls and ceilings throughout the school. At the time of the evaluation, abatement of LBP had been completed in approximately one-third of the school. One-hundred eighteen wipe samples for lead dust were collected from floors, teachers' desks, and interior window sills. Areas selected for sampling were based on the work location of the 45 participants providing blood for lead analysis. Wipe samples from hands were collected from all participants. The geometric means (GMs) for lead dust loadings on sills in unabated rooms (n = 23) and abated rooms (n = 16) were 342 and 102 micrograms/ft2, respectively. Nine sills in unabated rooms and one sill in an abated room exceeded the Housing and Urban Development (HUD) guidelines (500 micrograms/ft2 lead) for residential housing following abatement activity. GMs for lead loadings on floors in unabated rooms (n = 26) and abated rooms (n = 14) were 136 and 70 micrograms/ft2 lead, respectively. Seventeen floor samples from unabated rooms and 3 samples from abated rooms exceeded HUD guidelines (100 micrograms/ft2 lead). The GM blood lead level (BLL) was 2.2 micrograms/dL (range: 0.6-5.6 micrograms/dL), similar to that of the general U.S. population. Despite peeling LBP and significant lead dust loadings, a hazard from LBP was not found for staff at the school. There were no relationships between surface lead and hand lead, BLL and abatement status of assigned work area, or BLL and hand lead.

Occupational risk of Mycobacterium tuberculosis infection in hospital workers

We conducted a 4-year (1/89-12/92) retrospective cohort study among employees at a large metropolitan hospital where a nosocomial outbreak of multidrug-resistant tuberculosis (TB) had occurred. We compared the risk of tuberculin skin test (TST) conversion among employees who worked on wards where patients with culture-confirmed TB were cared for ("exposed") with the risk among employees who worked on wards with no such patients ("unexposed"). Exposed employees had a higher 4-year risk of TST conversion (14.5%) than unexposed employees (1.4%) (adjusted relative risk 13.4; 95 percent confidence interval 5.1-35.2). Exposed employees had significantly higher risks of conversion than unexposed employees during 1989-91, but not for 1992. Among the exposed, ward clerks had a risk of conversion (15.6%) only slightly lower than nurses (18.2%). We conclude that employees who worked in areas where patients with active M. tuberculosis infection were cared for, including workers who did not provide direct patient care, had a higher risk of TST conversion than employees who did not work in these areas. Reasons for the decline in risk over time include outbreak termination, fewer admissions of patients with TB, implementation of effective infection control measures, and possible resistance to infection in some members of the study population.

Hadamard transform imager and imaging spectrometer

An imager and a spectrometric imager, which achieve multiplexing by the use of binary optical encoding masks, have been built and tested. The masks are based on orthogonal, pseudorandom digital codes derived from Hadamard matrices. The spatial (and/or spectral) data are therefore obtained in the form of a Hadamard transform of the spatial (and/or spectral) scene; computer algorithms are used to decode the data and reconstruct images of the original scene. The hardware, algorithms processing and display facility are described. A number of spatial and spatial/spectral images, obtained in the laboratory, are presented. We present an analysis of the situations for which the multiplex advantage may be gained and of the limitations of the technique. Potential applications of the spectrometric imager are discussed. The spectrometric imager is covered by U.S. Patent 3,720,469 assigned to Spectral Imaging Inc., Concord, Mass.

Experimental realization of the multiplex advantage with a hadamard-transform spectrometer

A 255-slot Hadamard-transform spectrometer is described which has experimentally verified the multiplex advantage in signal-to-noise ratio previously predicted for this class of spectrometer.

Hadamard-transform exhaust-analysis spectrometer

We propose a novel instrument for automobile exhaust analysis based on a Hadamard-transform spectrometer, which would be able to make accurate measurements of the concentration of several pollutants simultaneously, would be operated by unskilled personnel, and would complete a measurement scan in less than 1 sec.

Hadamard-transform image scanning

We point out the applicability of optical Hadamard-transform coding to detector-noise-limited image scanning and give approximate signal-to-noise ratio gains over conventional point-by-point scanning for several whole-image multiplex scanning schemes.

Sequential encoding with multislit spectrometers

A new method for optically encoding the spectral output of multislit spectrometers is proposed. It is based on sequential measurements of the total intensity of light in combinations of selected spectral bands. The resulting encoded optical information is obtained as a set of simultaneous linear algebraic equations, and spectrum reconstruction is accomplished through the use of matrix inversion techniques. This encoding method avoids the problems associated with frequency transform encoding, because it is not based on the usual Fourier or Fresnel transforms. Rather, it makes use of the theory of simultaneous linear algebraic equations.