Håkan Geijer

Image quality vs. radiation dose for a flat-panel amorphous silicon detector: a phantom study.

Abstract. The aim of this study was to investigate the image quality for a flat-panel amorphous silicon detector at various radiation dose settings and to compare the results with storage phosphor plates and a screen-film system. A CDRAD 2.0 contrast-detail phantom was imaged with a flat-panel detector (Philips Medical Systems, Eindhoven, The Netherlands) at three different dose levels with settings for intravenous urography. The same phantom was imaged with storage phosphor plates at a simulated system speed of 200 and a screen-film system with a system speed of 160. Entrance surface doses were recorded for all images. At each setting, three images were read by four independent observers. The flat-panel detector had equal image quality at less than half the radiation dose compared with storage phosphor plates. The difference was even larger when compared with film with the flat-panel detector having equal image quality at approximately one-fifth the dose. The flat-panel detector has a very favourable combination of image quality vs radiation dose compared with storage phosphor plates and screen film.

The no-touch saphenous vein for coronary artery bypass grafting maintains a patency, after 16 years, comparable to the left internal thoracic artery : a randomized trial

OBJECTIVES This study investigates whether the no-touch (NT) vein graft, at a mean time of 16 years, maintains a significantly higher patency rate than conventional (C) vein grafts and still has patency comparable to that of the left internal thoracic artery (LITA). METHODS A total of 156 patients accepted for coronary artery bypass grafting were randomly allocated to 1 of 3 groups. In the C group, the saphenous vein (SV) was stripped and distended. In the intermediate group, the SV was stripped but not distended. In the NT group, the SV was neither stripped nor distended, but rather harvested with a fat pedicle. This study is an angiographic follow-up of the C and NT groups, at a mean time of 16 years postoperatively. RESULTS Fifty-four patients were included (C group = 27; NT group = 27). In all, 72 and 75 vein grafts were completed in groups C and NT, respectively. Crude SV graft patency was 64% in the C group versus 83% in the NT group (P = .03), which was similar to the patency of the LITA (88%). The harvesting technique had a major impact on the patency with a hazard ratio for occlusion of 1.83 for the C group (P = .04). CONCLUSIONS Harvesting the SV with the NT technique conferred, at a mean time of 16 years, a significantly higher patency than the conventional technique that was still comparable to that of the LITA.

Fascia suturing of large access sites after endovascular treatment of aortic aneurysms and dissections

Purpose: To evaluate a technique for closure of a femoral artery access in which the cribriform fascia covering the common femoral artery is sutured. Methods: A consecutive series of 127 patients (103 men; median age 74 years, range 45–89) underwent endovascular aortic aneurysm repair between August 2001 and September 2004. Twelve patients underwent a secondary intervention for a total of 139 procedures in the group. Sixty-one (43.9%) of the 139 operations were acute. Among the 257 femoral arteries used for access, a fascia suturing technique was performed in 131 (51.0%). Data were collected for analysis of access site complications, bleeding, thrombosis, pseudoaneurysm, and stenosis. A subgroup of 72 patients had ankle-brachial indexes (ABI) recorded; another subgroup of 50 patients were also investigated by duplex ultrasonography. Results: Complications occurred in 18 (13.7%) of the 131 sutured cases. The majority (n = 16) arose within 24 hours: 8 cases of perioperative bleeding or thrombosis required open surgery and 8 cases were reoperated within 24 hours for bleeding (n=4), thrombosis (n=3), and 1 intimal dissection. The acute failure rate was 12.2%. Two patients had late complications: 1 case of neuralgia and 1 pseudoaneurysm that required acute surgery 28 months postoperatively. The ABI did not change significantly from pre- to postoperatively in the 72 patients examined. Five patients with stenoses did not have a reduction in ABI. In the 66 sites examined with ultrasound in 50 patients, 3 minor pseudoaneurysms were detected. Conclusion: The fascia suturing technique for closure of a femoral artery access during endovascular repair of aortic diseases is feasible, even in acute situations. Failures can be managed easily. Late complications requiring additional procedures are rare.

Aspiration Induced by Remifentanil : A Double-blind, Randomized, Crossover Study in Healthy Volunteers

Background:Remifentanil is widely used for monitored anesthesia care in spontaneously breathing patients. However, the authors’ previous studies have shown that remifentanil induces subjective swallowing difficulties, which may increase the risk of aspiration. Methods:Twenty-five healthy volunteers participated in a double-blind, randomized, crossover trial at the University Hospital in Örebro, Örebro, Sweden. The volunteers were studied on two different occasions during which they received either remifentanil with an effect-site target concentration of 3 ng/ml or saline over 1 h. A radionuclide tracer was infused simultaneously into the nasopharynx at a rate of 0.1 ml/min. Aspiration was determined by lung scans, and subjective swallowing difficulties and grip strength were evaluated. The primary outcome was the difference in occurrence of aspiration between remifentanil and placebo treatments. The secondary outcomes were differences in swallowing difficulty and grip strength and the association between aspiration and swallowing difficulty. Results:During remifentanil and placebo infusion, 48 and 12% of the volunteers aspirated, respectively, difference: 36% (95% CI, 10 to 62%). A similar significant difference was found for swallowing difficulties but not for the association between aspiration and swallowing. No difference was found in grip strength between the two treatments. Conclusions:Remifentanil infusion at concentrations used in monitored anesthesia care increases the incidence of aspiration. However, the subjective swallowing difficulty induced by remifentanil is not indicative of the aspiration risk.

Optimizing the tube potential for lumbar spine radiography with a flat-panel digital detector

The purpose of this study was to find the optimal settings for lumbar spine radiography with a flat-panel detector. A CDRAD contrast-detail phantom was imaged at various tube potentials, system speeds and filtration settings. Factorial experiments yielded a range of optimized exposure settings, which were submitted to visual grading analysis with images of an Alderson phantom. The first optimized settings involved a system speed increase from 400 to 800. For anteroposterior projection, the optimal tube potential was reduced from the default of 77 kV to 60 kV to give the best image quality without increasing the effective dose, or to 66 kV to give the lowest dose without reducing image quality. For lateral projection, the tube potential was similarly reduced from the default of 90 kV to 70 kV or 77 kV. Visual grading analysis confirmed the results, with significantly better image quality when optimizing for image quality. The study thus shows that the tube potential can be reduced as long as the system speed is increased simultaneously. This leads to a lower effective dose and/or increased image quality depending on the settings chosen. The factorial experiments provided a powerful way to evaluate several parameters concomitantly.

A Clinical Evaluation of the Image Quality Computer Program, CoCIQ

To provide an objective way of measuring image quality, a computer program was designed that automatically analyzes the test images of a contrast-detail (CD) phantom. The program gives a quantified measurement of image quality by calculating an Image Quality Figure (IQF). The aim of this work was to evaluate the program and adjust it to clinical situations in order to find the detectable level where the program gives a reliable figure of the contrast resolution. The program was applied on a large variety of images with lumbar spine and urographic parameters, from very low to very high image qualities. It was shown that the computer program produces IQFs with small variations and there were a strong linear statistical relation between the computerized evaluation and the evaluation performed by human observers (R2 = 0.98). This method offers a fast and easy way of conducting image quality evaluations.

Coaxial technique for catheterization of the coronary arteries with a very dilated ascending aorta

This article describes a simple yet effective method to catheterize the coronary arteries when the ascending aorta is very dilated. Two catheters are used in a coaxial fashion. It was possible to catheterize a patient with a 9 cm wide ascending aorta. Catheter Cardiovasc Interv 2004;62:32–34.

Low-dose computed tomography of the lumbar spine : a phantom study on imaging parameters and image quality

Background Lumbar spine radiography has limited diagnostic value but low radiation dose compared with computed tomography (CT). The average effective radiation dose from lumbar spine radiography is about 1.1 mSv. Low-dose lumbar spine CT may be an alternative to increase the diagnostic value at low radiation dose, around 1 mSv. Purpose To determine the optimal settings for low-dose lumbar spine CT simultaneously aiming for the highest diagnostic image quality possible. Material and Methods An ovine lower thoracic and lumbar spine phantom, with all soft tissues around the vertebrae preserved except the skin, was placed in a 20 L plastic container filled with water. The phantom was scanned repeatedly with various technical settings; different tube potential, reference mAs, and with different convolution filters. Five radiologists evaluated the image quality according to a modification of the European guidelines for multislice computed tomography (MSCT) quality criteria for lumbar spine CT 2004. In a visual comparison the different scans were also ranked subjectively according to perceived image quality. Image noise and contrast were measured. Results A tube potential of 120 kV with reference mAs 30 and medium or medium smooth convolution filter gave the best image quality at a sub-millisievert dose level, i.e. with an effective dose comparable to that from lumbar spine radiography. Conclusion Low-dose lumbar spine CT thus opens a possibility to substitute lumbar spine radiography with CT without obvious increase in radiation dose.

Temperature measurements with a temporal scanner: systematic review and meta-analysis.

Objectives Systematic review and meta-analysis on the diagnostic accuracy of temporal artery thermometers (TAT). Design Systematic review and meta-analysis. The index test consisted of temperature measurement with TAT. The reference test consisted of an estimation of core temperature. Participants Clinical patients as well as healthy participants, with or without fever. Interventions Literature search in PubMed, Embase, Cinahl and Web of Science. Three reviewers selected articles for full-text reading after which a further selection was made. Risk of bias was assessed with QUADAS-2. Pooled difference and limits of agreement (LoA) were estimated with an inverse variance weighted approach. Subgroup and sensitivity analyses were performed. Sensitivity and specificity were estimated using hierarchical models. Quality of evidence was assessed according to the GRADE system. Primary and secondary outcome measures The primary outcome was measurement accuracy expressed as mean difference ±95% LoA. A secondary outcome was sensitivity and specificity to detect fever. If tympanic thermometers were assessed in the same population as TAT, these results were recorded as well. Results 37 articles comprising 5026 participants were selected. Pooled difference was -0.19°C (95% LoA −1.16 to 0.77°C), with moderate quality of evidence. Pooled sensitivity was 0.72 (95% CI 0.61 to 0.81) with a specificity of 0.94 (95% CI 0.87 to 0.97). The subgroup analysis revealed a trend towards underestimation of the temperature for febrile patients. There was a large heterogeneity among included studies with wide LoA which reduced the quality of evidence. Conclusions TAT is not sufficiently accurate to replace one of the reference methods such as rectal, bladder or more invasive temperature measurement methods. The results are, however, similar to those with tympanic thermometers, both in our meta-analysis and when compared with others. Thus, it seems that TAT could replace tympanic thermometers with the caveat that both methods are inaccurate. Trial registration number CRD42014008832.

Virtual non-contrast dual-energy CT compared to single-energy CT of the urinary tract: a prospective study

Background Dual-energy computed tomography (DECT) has been shown to be useful for subtracting bone or calcium in CT angiography and gives an opportunity to produce a virtual non-contrast-enhanced (VNC) image from a series where contrast agents have been given intravenously. High noise levels and low resolution have previously limited the diagnostic value of the VNC images created with the first generation of DECT. With the recent introduction of a second generation of DECT, there is a possibility of obtaining VNC images with better image quality at hopefully lower radiation dose compared to the previous generation. Purpose To compare the image quality of the single-energy series to a VNC series obtained with a two generations of DECT scanners. CT of the urinary tract was used as a model. Material and Methods Thirty patients referred for evaluation of hematuria were examined with an older system (Somatom Definition) and another 30 patients with a new generation (Somatom Definition Flash). One single-energy series was obtained before and one dual-energy series after administration of intravenous contrast media. We created a VNC series from the contrast-enhanced images. Images were assessed concerning image quality with a visual grading scale evaluation of the VNC series with the single-energy series as gold standard. Results The image quality of the VNC images was rated inferior to the single-energy variant for both scanners, OR 11.5–67.3 for the Definition and OR 2.1–2.8 for the Definition Flash. Visual noise and overall quality were regarded as better with Flash than Definition. Conclusion Image quality of VNC images obtained with the new generation of DECT is still slightly inferior compared to native images. However, the difference is smaller with the new compared to the older system.