Portable computed tomography performed on the intensive care unit

Initial experience with a state-of-the-art mobile head CT scanner for use in neurointensive care units

OBJECTIVE

Mobile head computed tomography (CT) scanners can reduce transport-related complications in neurointensive care unit (NICU) patients and decrease the burden on NICU staff; however, the initial investment cost and reduced image quality of early mobile scanners have prevented their widespread clinical use. Here, we report our initial experience with a novel 32-row mobile CT scanner for use in NICUs.

METHODS

Over a 2-year period, 107 patients received a mobile head CT scan. The technical characteristics of the scanner and the organizational procedures are described in detail. Patient characteristics were retrospectively collected and image quality was subjectively evaluated on a Likert scale ranging from 0 to 5 and compared with a stationary CT scanner.

RESULTS

Mobile head CT was used for follow-up of intracranial hemorrhage in 51%, routine postoperative imaging in 28%, evaluation of neurological deterioration in 14%, bedside monitoring after external ventricular drain placement in 4%, and follow-up of ischemic stroke in 3% of cases. Diagnostic imaging quality was achieved in all cases, eliminating the need for stationary CT scanning. The overall image quality of mobile CT (median 4 points) was inferior to that of conventional stationary CT (median 5 points, p < 0.01), but was rated with 4 or 5 points in the majority of cases.

CONCLUSIONS

State-of-the-art mobile CT was found to be easy to use and maneuver and has the potential to expedite the diagnosis of NICU patients and reduce staff workload. Image quality was adequate for common NICU issues.

State-of-the-art mobile head CT scanner delivers nearly the same image quality as a conventional stationary CT scanner

The use of mobile head CT scanners in the neurointensive care unit (NICU) saves time for patients and NICU staff and can reduce transport-related mishaps, but the reduced image quality of previous mobile scanners has prevented their widespread clinical use. This study compares the image quality of SOMATOM On.Site (Siemens Healthineers, Erlangen, Germany), a state-of-the-art mobile head CT scanner, and a conventional 64-slice stationary CT scanner. The study included 40 patients who underwent head scans with both mobile and stationary scanners. Gray and white matter signal and noise were measured at predefined locations on axial slices, and signal-to-noise ratios (SNRs) and contrast-to-noise ratios (CNRs) were calculated. Artifacts below the cranial calvaria and in the posterior fossa were also measured. In addition, image quality was subjectively assessed by two radiologists in terms of corticomedullary differentiation, subcalvarial space, skull artifacts, and image noise. Quantitative measurements showed significantly higher image quality of the stationary CT scanner in terms of noise, SNR and CNR of gray and white matter. Artifacts measured in the posterior fossa were higher with the mobile CT scanner, but subcalvarial artifacts were comparable. Subjective image quality was rated similarly by two radiologists for both scanners in all domains except image noise, which was better for stationary CT scans. The image quality of the SOMATOM On.Site for brain scans is inferior to that of the conventional stationary scanner, but appears to be adequate for daily use in a clinical setting based on subjective ratings.

Limited Evaluation of Image Quality Produced by a Portable Head CT Scanner (CereTom) in a Neurosurgery Centre

INTRODUCTION

Computed tomography (CT) is the preferred diagnostic toolkit for head and brain imaging of head injury. A recent development is the invention of a portable CT scanner that can be beneficial from a clinical point of view.

AIM

To compare the quality of CT brain images produced by a fixed CT scanner and a portable CT scanner (CereTom).

METHODS

This work was a single-centre retrospective study of CT brain images from 112 neurosurgical patients. Hounsfield units (HUs) of the images from CereTom were measured for air, water and bone. Three assessors independently evaluated the images from the fixed CT scanner and CereTom. Streak artefacts, visualisation of lesions and grey-white matter differentiation were evaluated at three different levels (centrum semiovale, basal ganglia and middle cerebellar peduncles). Each evaluation was scored 1 (poor), 2 (average) or 3 (good) and summed up to form an ordinal reading of 3 to 9.

RESULTS

HUs for air, water and bone from CereTom were within the recommended value by the American College of Radiology (ACR). Streak artefact evaluation scores for the fixed CT scanner was 8.54 versus 7.46 (Z = -5.67) for CereTom at the centrum semiovale, 8.38 (SD = 1.12) versus 7.32 (SD = 1.63) at the basal ganglia and 8.21 (SD = 1.30) versus 6.97 (SD = 2.77) at the middle cerebellar peduncles. Grey-white matter differentiation showed scores of 8.27 (SD = 1.04) versus 7.21 (SD = 1.41) at the centrum semiovale, 8.26 (SD = 1.07) versus 7.00 (SD = 1.47) at the basal ganglia and 8.38 (SD = 1.11) versus 6.74 (SD = 1.55) at the middle cerebellar peduncles. Visualisation of lesions showed scores of 8.86 versus 8.21 (Z = -4.24) at the centrum semiovale, 8.93 versus 8.18 (Z = -5.32) at the basal ganglia and 8.79 versus 8.06 (Z = -4.93) at the middle cerebellar peduncles. All results were significant with P-value < 0.01.

CONCLUSIONS

Results of the study showed a significant difference in image quality produced by the fixed CT scanner and CereTom, with the latter being more inferior than the former. However, HUs of the images produced by CereTom do fulfil the recommendation of the ACR.

Head computed tomography scanning during pediatric neurocritical care: diagnostic yield and the utility of portable studies

BACKGROUND

We report our use of portable head computed tomography (CT) and the diagnostic yield and radiation dose from head CT in the pediatric intensive care unit (PICU).

METHODS

204 PICU patients underwent head CT during 2008-2009. Therapeutic interventions and resource intensity during CT were categorized. Severity of illness was summarized using the pediatric risk of mortality (PRISM-III) model. Estimates of patient radiation dose were based on dose measurements made in four anthropomorphic head phantoms.

RESULTS

242 (62%) out of 391 head CT studies were portable. New pathology was identified on 80 (40%) scans. CT findings prompted a change in management in 46 (23%) patients; 25 of these resulted in life-extending treatments and 21 had forgoing of life-sustaining treatments within 24 hours. 26 patients with PRISM score greater than 30% underwent CT; 23 (88%) of these were portable. More portable versus fixed examinations were performed in patients requiring extracorporeal membrane oxygenation, inhaled nitric oxide, high levels of positive end expiratory pressure, and those with high vasopressor scores (P < 0.05). Estimated patient dose from portable CT was 83 ± 6 mGy compared to 72 ± 5 mGy for patients imaged on a fixed scanner (P < 0.0001).

CONCLUSION

Two-thirds of CT scans obtained in the PICU were portable because of patients' intensity of therapy and illness severity. Portable CT showed major new pathology in greater than 1/3 and led to a change in management in 1/4 of higher acuity patients scanned. The estimated radiation dose from portable CT is within the current national guidelines.

Review of portable CT with assessment of a dedicated head CT scanner

This article reviews a number of portable CT scanners for clinical imaging. These include the CereTom, Tomoscan, xCAT ENT, and OTOscan. The Tomoscan scanner consists of a gantry with multisection detectors and a detachable table. It can perform a full-body scanning, or the gantry can be used without the table to scan the head. The xCAT ENT is a conebeam CT scanner that is intended for intraoperative scanning of cranial bones and sinuses. The OTOscan is a multisection CT scanner intended for imaging in ear, nose, and throat settings and can be used to assess bone and soft tissue of the head. We also specifically evaluated the technical and clinical performance of the CereTom, a scanner designed specifically for neuroradiologic head imaging. The contrast performance of this scanner permitted the detection of 4-mm low-contrast lesions, and the limiting spatial resolution was 7 line pairs per centimeter. The measured volume of the CT dose index (CTDI(vol)) for a standard head CT scan was 41 mGy (120 kV/14 mAs). All clinical images were of diagnostic quality, and the average patient effective dose was 1.7 mSv. We conclude that the CereTom portable CT scanner generates satisfactory clinical images at acceptable patient doses.

Detection of lung atelectasis/consolidation by ultrasound in multiple trauma patients with mechanical ventilation

Objective

To evaluate the efficacy of bedside ultrasound in detecting lung atelectasis/consolidation in multiple trauma patients with mechanical ventilation.

Methods

This prospective observation study was conducted in the emergency intensive care unit (EICU) over an 18-month period from January 2007 to June 2008. Chest ultrasound was performed in 81 multiple trauma patients with mechanical ventilation. Computed tomography (CT) was regarded as the “golden standard” to diagnose lung atelectasis/consolidation.

Results

Computed tomography detected 154 lung atelectasis/consolidation in 324 lung regions in 81 patients. Ultrasound confirmed 126 lung atelectasis/consolidation, 87 with complete and 39 with incomplete atelectasis/consolidation. The sensitivity, specificity, positive predictive value, negative predictive value and accuracy of ultrasound were 81.8, 100, 100, 85.9 and 91.4%, respectively. A Kappa agreement test showed a very high concordance between ultrasound and CT with a Kappa coefficient of 0.825 (P = 0.031). The effective ratio of ultrasound guiding lung recruitment was 80.2%.

Conclusion

Ultrasound is a safe, dynamic viewing and accurate method to diagnose and manage lung atelectasis/consolidation in multiple trauma patients with mechanical ventilation.

[Electrical impedance tomography: ready for routine clinical use for mechanically ventilated patients?]

Electrical impedance tomography (EIT) is a non-invasive, radiation-free functional imaging technique, which offers the possibility of continuous bedside measurement of regional lung ventilation. The principle of EIT is based on the input of alternating current and voltage measurement via surface electrodes placed around the thorax, which measure changes of electrical impedance parallel to changes in aeration within the lungs. This enables the measurement of regional ventilation. Because of the rapid time resolution of this technique, it can be used for the measurement of fast physiological effects. For more than 20 years EIT has been intensively used for research purposes, but has not yet been used for the monitoring of regional lung function in the routine clinical setting. This review describes the status of EIT in the clinical routine, its possibilities and limitations.

Low spatial resolution computed tomography underestimates lung overinflation resulting from positive pressure ventilation*

OBJECTIVE

In acute lung injury, lung overinflation resulting from mechanical ventilation with positive end-expiratory pressure (PEEP) can be assessed using lung computed tomography. The goal of this study was to compare lung overinflation measured on low and high spatial resolution computed tomography sections.

DESIGN

Lung overinflation was measured on thick (10-mm) and thin (1.5-mm) computed tomography sections obtained at zero end-expiratory pressure (ZEEP) and PEEP 10 cm H2O using a software including a color-coding system.

SETTING

A 20-bed surgical intensive care unit of a university hospital.

PATIENTS

Thirty mechanically ventilated patients with acute lung injury.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Overinflated lung volume was measured as the end-expiratory volume of lung regions with computed tomography attenuations <-900 Hounsfield units. Lung overinflation, expressed in percentage of the total lung volume, was significantly underestimated by thick computed tomography sections compared with thin computed tomography sections (0.4 +/- 1.6% vs. 3.0 +/- 4.0% in ZEEP and 1.9 +/- 4% vs. 6.8 +/- 7.3% in PEEP, p < .01). In patients with a diffuse loss of aeration, the overinflated lung volumes of thick and thin computed tomography sections were, respectively, 0.6 +/- 0.8 mL vs. 16 +/- 10 mL in ZEEP (p < .01) and 8 +/- 9 mL vs. 73 +/- 62 mL in PEEP (p < .05). In patients with a focal loss of aeration, this underestimation was more pronounced: 18 +/- 56 mL vs. 127 +/- 140 mL in ZEEP (p < .01) and 85 +/- 161 mL vs. 322 +/- 292 mL in PEEP (p < .01).

CONCLUSIONS

In patients with acute lung injury, an accurate computed tomography estimation of lung overinflation resulting from positive pressure mechanical ventilation requires high spatial resolution computed tomography sections, particularly when the lung morphology shows a focal loss of aeration.