Radiation dose reduction in postoperative computed position control of cochlear implant electrodes in lambs - An experimental study.

OBJECTIVE: Cochlear implants (CI) are standard treatment for prelingually deafened children and postlingually deafened adults. Computed tomography (CT) is the standard method for postoperative imaging of the electrode position. CT scans accurately reflect electrode depth and position, which is essential prior to use. However, routine CT examinations expose patients to radiation, which is especially problematic in children. We examined whether new CT protocols could reduce radiation doses while preserving diagnostic accuracy. METHODS: To investigate whether electrode position can be assessed by low-dose CT protocols, a cadaveric lamb model was used because the inner ear morphology is similar to humans. The scans were performed at various volumetric CT dose-indexes CTDIvol)/kV combinations. For each constant CTDIvol the tube voltage was varied (i.e., 80, 100, 120 and 140kV). This procedure was repeated at different CTDIvol values (21mGy, 11mGy, 5.5mGy, 2.8mGy and 1.8mGy). To keep the CTDIvol constant at different tube voltages, the tube current values were adjusted. Independent evaluations of the images were performed by two experienced and blinded neuroradiologists. The criteria diagnostic usefulness, image quality and artifacts (scaled 1-4) were assessed in 14 cochlear-implanted cadaveric lamb heads with variable tube voltages. RESULTS: Results showed that the standard CT dose could be substantially reduced without sacrificing diagnostic accuracy of electrode position. The assessment of the CI electrode position was feasible in almost all cases up to a CTDIvol of 2-3mGy. The number of artifacts did not increase for images within this dose range as compared to higher dosages. The extent of the artifacts caused by the implanted metal-containing CI electrode does not depend on the radiation dose and is not perceptibly influenced by changes in the tube voltage. Summarizing the evaluation of the CI electrode position is possible even at a very low radiation dose. CONCLUSIONS: CT imaging of the temporal bone for postoperative electrode position control of the CI is possible with a very low and significantly radiation dose. The tube current-time product and voltage can be reduced by 50% without increasing artifacts. Low-dose postoperative CT scans are sufficient for localizing the CI electrode.

Heterotopic Pregnancy after Natural Conception: A Case Report.

Heterotopic pregnancy (HP), i.e. the simultaneous development of an intrauterine and an ectopic pregnancy, is rare with a reported incidence of between 1 : 2600 and 1 : 30 000. Only a few cases have been described in the literature. We report here on an extremely rare case of HP after natural conception with cardiac activity noted on sonography in both the intrauterine and the ectopic foetus. Examination excluded appendicitis. Vaginal sonography (VS) was performed and revealed a second, extrauterine foetus with cardiac activity. The differential diagnosis included twin pregnancy in a bicornuate uterus, but HP could not be excluded. Diagnostic laparoscopy was scheduled due to progressive abdominal pain. Shortly before surgery the patient became acutely hypotensive. Laparoscopy confirmed a heterotopic pregnancy in the right tube. Due to acute rupture of the extrauterine pregnancy with intraabdominal bleeding, the procedure was converted to a laparotomy with right-sided salpingectomy. Subsequently, the intrauterine pregnancy continued without complications. The intrauterine pregnancy was uneventful with spontaneous delivery at term.

Low-dose temporal bone CT in infants and young children: effective dose and image quality.

BACKGROUND AND PURPOSE: The temporal bone is ideal for low-dose CT because of its intrinsic high contrast. The aim of this study was to retrospectively evaluate image quality and radiation doses of a new low-dose versus a standard high-dose pediatric temporal bone CT protocol and to review dosimetric data from the literature. MATERIALS AND METHODS: Image quality and radiation doses were compared for 38 low-dose (80 kV/90-110 mAs) and 16 high-dose (140 kV/170 mAs) temporal bone CT scans of infants to 5-year-old children. The CT visualization quality of 23 middle and inner ear structures was subjectively graded by 3 neuroradiologists and 3 otologists by using a 5-point scale with scores 1-2 indicating insufficient and scores 3-5 indicating sufficient image quality. Effective doses of local and literature-derived protocols were calculated from dosimetric data by using NRPB-SR250 software. RESULTS: Insufficient image-quality scores were more frequent in low-dose scans versus high-dose scans, but the difference was only statistically significant for otologists (6.0% versus 3.4%, P = .004) and not for neuroradiologists (1.2% versus 0.7%, P = .84). Image quality was critical for small structures (such as the stapes or lamella at the internal auditory canal fundus). Effective doses were 0.25-0.3 mSv for low-dose scans, 1.4-1.8 mSv for high-dose scans, and 0.9-2.6 mSv for literature-derived protocols. CONCLUSIONS: The image quality of the new low-dose protocol remains diagnostic for assessing middle and inner ear anatomy despite a 3- to 8-fold dose reduction over previous and literature-derived protocols. However, image quality of small structures is critical and may be perceived as insufficient.

Development of an auditory implant manipulator for minimally invasive surgical insertion of implantable hearing devices.

OBJECTIVE: To present the auditory implant manipulator, a navigation-controlled mechanical and electronic system which enables minimally invasive ('keyhole') transmastoid access to the tympanic cavity. MATERIALS AND METHODS: The auditory implant manipulator is a miniaturised robotic system with five axes of movement and an integrated drill. It can be mounted on the operating table. We evaluated the surgical work field provided by the system, and the work sequence involved, using an anatomical whole head specimen. RESULTS: The work field provided by the auditory implant manipulator is considerably greater than required for conventional mastoidectomy. The work sequence for a keyhole procedure included pre-operative planning, arrangement of equipment, the procedure itself and post-operative analysis. CONCLUSION: Although system improvements are necessary, our preliminary results indicate that the auditory implant manipulator has the potential to perform keyhole insertion of implantable hearing devices.

[Strategies for reducing the CT radiation dose]. / Strategien zur reduktion der CT-strahlendosis.

The rapid technical advances in computed tomography have led to an increased number of clinical indications. Unfortunately, at the same time the radiation exposure to the population has also increased due to the increased total number of CT examinations. In the last few years various publications have demonstrated the feasibility of radiation dose reduction for CT examinations with no compromise in image quality and loss in interpretation accuracy. The majority of the proposed methods for dose optimization are easy to apply and are independent of the detector array configuration. This article reviews indication-dependent principles (e.g. application of reduced tube voltage for CT angiography, selection of the collimation and the pitch, reducing the total number of imaging series, lowering the tube voltage and tube current for non-contrast CT scans), manufacturer-dependent principles (e.g. accurate application of automatic modulation of tube current, use of adaptive image noise filter and use of iterative image reconstruction) and general principles (e.g. appropriate patient-centering in the gantry, avoiding over-ranging of the CT scan, lowering the tube voltage and tube current for survey CT scans) which lead to radiation dose reduction.

Acute transverse myelitis in Lyme neuroborreliosis.

INTRODUCTION: Acute transverse myelitis (ATM) is a rare disorder (1-8 new cases per million of population per year), with 20% of all cases occurring in patients younger than 18 years of age. Diagnosis requires clinical symptoms and evidence of inflammation within the spinal cord (cerebrospinal fluid and/or magnetic resonance imaging). ATM due to neuroborreliosis typically presents with impressive clinical manifestations. CASE PRESENTATION: Here we present a case of Lyme neuroborreliosis-associated ATM with severe MRI and CSF findings, but surprisingly few clinical manifestations and late conversion of the immunoglobulin G CSF/blood index of Borrelia burgdorferi sensu lato. CONCLUSION: Clinical symptoms and signs of neuroborrelial ATM may be minimal, even in cases with severe involvement of the spine, as shown by imaging studies. The CSF/blood index can be negative in the early stages and does not exclude Lyme neuroborreliosis; if there is strong clinical suspicion of Lyme neuroborreliosis, appropriate treatment should be started and the CSF/blood index repeated to confirm the diagnosis.

CT radiation dose for computer-assisted endoscopic sinus surgery: dose survey and determination of dose-reduction limits.

BACKGROUND AND PURPOSE: Computer-assisted navigation is increasingly used in functional endoscopic sinus surgery (FESS) to prevent injury to vital structures, necessitating preparative CT and, thus, radiation exposure. The purpose of our study was to investigate currently used radiation doses for CT in computer-assisted navigation in sinus surgery (CAS-CT) and to assess minimal doses required. MATERIALS AND METHODS: A questionnaire inquiring about dose parameters used for CAS-CT was sent to 30 radiologic institutions. The feasibility of low-dose registration was tested with a phantom. The influence of CAS-CT dose on technical accuracy and on the practical performance of 5 ear, nose, and throat (ENT) surgeons was evaluated with cadaver heads. RESULTS: The questionnaire response rate was 63%. Variation between minimal and maximal dose used for CAS-CT was 18-fold. Phantom registration was possible with doses as low as 1.1 mGy. No dose dependence on technical accuracy was found. ENT surgeons were able to identify anatomic landmarks on scans with a dose as low as 3.1 mGy. CONCLUSIONS: The vast dose difference between institutions mirrors different attitudes toward image quality and radiation-protection issues rather than being technically founded, and many patients undergo CAS-CT at higher doses than necessary. The only limit for dose reduction in CT for computer-assisted endoscopic sinus surgery is the ENT surgeon's ability to cope with impaired image quality, whereas there is no technically justified lower dose limit. We recommend, generally, doses used for the typical diagnostic low-dose sinus CT (120 kV/20-50 mAs). When no diagnostic image quality is needed, even a reduction down to a third is possible.

Effective doses from scan projection radiographs of the head: impact of different scanning practices and comparison with conventional radiography.

BACKGROUND AND PURPOSE: For CT scan planning, scan projection radiographs (SPR) are used. Tube tension and current for head SPR can be reduced to a minimum because of the small head diameter and because only high-contrast structures need to be visualized for planning. The goal of this study was to investigate SPR of the head in respect to effective doses, the influence of dose-reduction measures, and comparison with conventional x-ray. MATERIALS AND METHODS: Entrance doses for default and minimal settings were measured on a LightSpeed Ultra CT scanner and on conventional x-ray equipment. Effective doses for different scanning fields of the head were calculated for an adult, a 10-year-old child, and a neonate by using the commercially available software PCXMC. RESULTS: Depending on projection and technique, SPR effective doses for adults were 1.9-27.7 muSv; for the 10-year-old child, 2.1-31.1 muSv; and for the neonate, 5.2-97.2 muSv. Doses with the tube under the table were 1.3-3.4 times lower. Doses for conventional radiography were higher than SPR doses for adults and partially lower for children. CONCLUSIONS: Depending on the scanning technique, effective doses for head SPR can differ up to 17-fold. The dose is significantly reduced by lowering tube voltage and current, by positioning the tube under the table, and by keeping the thyroid out of the scan or by protecting it with a lead collar. Compared with the conventional x-ray technique, SPR doses tend to be lower due to x-ray beam characteristics.