[Value of CT and transthoracic lung ultrasound in patients with systemic sclerosis : Joint statement of the ÖRG/ÖGP/ÖGR/ÖGUM]. / Wertigkeit der CT und des transthorakalen Lungenultraschalls bei PatientInnen mit systemischer Sklerose : Gemeinsame Stellungnahme der ÖRG/ÖGP/ÖGR/ÖGUM.

Lung involvement is the most frequent cause of death in patients with systemic sclerosis (SSc). As lung involvement is frequently asymptomatic, the current recommendation is to carry out thoracic computed tomography (CT) in all patients newly diagnosed with SSc. There is currently disagreement on how patients with SSc for whom no lung involvement was found at the time of diagnosis, should be followed up. Based on a consensus of Austrian rheumatologists, pneumologists and radiologists it is recommended that for asymptomatic patients with a negative CT at the time of initial diagnosis, a transthoracic ultrasound examination should be carried out annually and a lung function examination every 6-12 months. In the presence of a positive lung ultrasound finding a supplementary CT for further clarification is recommended. Based on the data situation, annual CT follow-up controls are recommended for patients with a high risk as defined by appropriate risk factors.

[Adverse effects of immunotherapy : Clinical aspects, radiological and nuclear medicine results]. / Unerwünschte Wirkungen der Immuntherapie : Klinik, radiologische und nuklearmedizinische Befunde.

BACKGROUND: The increasing use of immunotherapy in oncology increases the need for radiologic evaluation of frequent and severe immune-related adverse events. OBJECTIVE: Determination of the incidence and manifestation of radiologic and nuclear medicine findings of immune-related adverse events. MATERIAL AND METHODS: Literature review of clinical and imaging findings of immune-related adverse events induced by the immune checkpoint inhibitors ipilimumab, nivolumab and pembrolizumab. Findings are illustrated with pictorial examples and contrasted to other relevant differential diagnoses. RESULTS: The most frequent imaging manifestations are colitis, hepatitis, pancreatitis, hypophysitis, pneumonitis, arthritis and sarcoid-like lymphadenopathy. Severe to life-threatening complications may result from colitis, pneumonitis and hypophysitis. A clear differentiation from other autoimmune diseases and discrimination of immune-related and infectious pulmonary findings can be very difficult and need close multidisciplinary collaboration. CONCLUSION: Knowledge of clinical and imaging findings of adverse events induced by immunotherapy is essential for timely and adequate therapeutic decisions. In addition to staging and follow-up imaging, identification and monitoring of immune-related adverse events adds to the radiologic responsibility in oncologic care.

68Ga-DOTA-TOC uptake in neuroendocrine tumour and healthy tissue: differentiation of physiological uptake and pathological processes in PET/CT.

PURPOSE: We wanted to establish the range of (68)Ga-DOTA-TOC uptake in liver and bone metastases of patients with neuroendocrine tumours (NET) and to establish the range of its uptake in pancreatic NET. This would allow differentiation between physiological uptake and tumour-related somatostatin receptor expression in the pancreas (including the uncinate process), liver and bone. Finally, we wanted to test for differences in patients with NET, either treated or not treated with peptide receptor radionuclide therapy (PRRT). METHODS: In 249 patients, 390 (68)Ga-DOTA-TOC PET/CT studies were performed. The clinical indications for PET/CT were gastroenteropancreatic NET (194 studies), nongastroenteropancreatic NET (origin in the lung and rectum; 46 studies), NET of unknown primary (111 studies), phaeochromocytoma/glomus tumours (18 studies), and radioiodine-negative metastatic thyroid carcinoma (21 studies). RESULTS: SUVmax (mean ± standard deviation) values of (68)Ga-DOTA-TOC were 29.8 ± 16.5 in 162 liver metastases, 19.8 ± 18.8 in 89 bone metastases and 34.6 ± 17.1 in 43 pancreatic NET (33.6 ± 14.3 in 30 tumours of the uncinate process and 36.3 ± 21.5 in 13 tumours of the pancreatic tail). A significant difference in SUVmax (p < 0.02) was found in liver metastases of NET patients treated with PRRT. There were significant differences in SUVmax between nonmalignant and malignant tissue for both bone and liver metastases and for pancreatic NET including the uncinate process (p < 0.0001). At a cut-off value of 17.1 the specificity and sensitivity of SUVmax for differentiating tumours in the uncinate process were 93.6 % and 90.0 %, respectively (p < 0.0001). CONCLUSION: (68)Ga-DOTA-TOC is an excellent tracer for the imaging of tumours expressing somatostatin receptors on the tumour cell surface, facilitating the detection of even small tumour lesions. The noninvasive PET/CT approach by measurement of regional SUVmax can offer important clinical information to distinguish between physiological and pathological somatostatin receptor expression, especially in the uncinate process. PRRT does not significantly influence SUVmax, except in liver metastases of patients with NET.

[Stereotaxy and robotics for ablation - toy or tool?]. / Stereotaxie und Robotik zur Ablation - Spielzeug oder Werkzeug?

CLINICAL AND METHODOLOGICAL ISSUES: Ablative technologies allow local curative tumor treatment by thermal tissue damage. An important prerequisite is the coverage of all tumor cells. Tumor size is the most important limiting factor. STANDARD RADIOLOGICAL METHODS: The drawbacks of conventional computed tomography/ultrasound/magnetic resonance imaging (CT/US/MRI) guided radiofrequency ablation (RFA) are the absence of planning software, imprecise probe placement, imprecise control of probe placement and the ablation zone as well as the lack of reliability and reproducibility. METHODOLOGICAL INNOVATIONS: Stereotactic and robot-assisted systems allow planning of multiple probe positions based on CT/MRI and positron emission tomography (PET) planning data. The probes can be precisely placed according to the coordinates of the image datasets. PERFORMANCE: The 1 and 3 year survival rates after stereotactic RFA (SRFA) of cholangiocellular carcinoma were 91% and 70% respectively and the median overall survival was 60 months. After SRFA of 189 colorectal liver metastases in 63 patients there was no significant difference in local recurrence rates between tumors < 3 cm (17.7%), 3-5 cm (11.1%) and > 5 cm (17.4%). The median overall survival was 33.2 months and the 1, 3, and 5 year overall survival rates after SRFA in patients with resectable colorectal cancer were 92%, 66% and 48%, respectively. ACHIEVEMENTS: In our opinion the excellent and, to a large extent user-independent results justify the increased efforts in time and costs especially for the treatment of patients with large and irregular tumors. PRACTICAL RECOMMENDATIONS: Stereotaxy and robotics are valuable tools for effective tumor ablation especially of large tumors and are likely to gain in importance in the next few years.

Optimizing ultrasound-guided biopsy of musculoskeletal masses by application of an ultrasound contrast agent.

PURPOSE: We report on a novel approach to the work-up of musculoskeletal lesions with addition of an ultrasound contrast agent followed by focal ultrasound-guided biopsy. MATERIALS AND METHODS: In this pilot study 25 patients (age: 12-75) with unclear musculoskeletal tumors underwent grayscale ultrasound, color Doppler, contrast-enhanced ultrasound and subsequent ultrasound-guided biopsy. Grayscale and color Doppler ultrasound were performed with a 12-5 MHz broadband linear transducer and contrast-enhanced ultrasound with a 9-3 MHz broadband linear transducer (iU22®, Philips, USA) using a second-generation contrast agent (SonoVue®, Bracco, Italy). After the definition of the target area by contrast-enhanced ultrasound, guided biopsies were performed with a spring-loaded tru-cut™ biopsy needle using the coaxial technique. RESULTS: The definition of enhancing and viable tumor regions resulted in a diagnostic yield of the subsequent biopsy of 100%. Seventeen tumors were classified as malignant and eight as benign, which was finally confirmed by histological work-up or the further clinical follow-up. CONCLUSION: This pilot study with a limited series of patients improved the diagnostic yield of ultrasound-guided biopsy to 100%, which is at least rather promising. Our easy-to-use algorithm should reduce the rate of inconclusive histology results mainly caused by sampling errors to an unrivaled minimum.

Navigated open, laparoscopic, and percutaneous liver surgery.

Resection and thermal ablation procedures are frequently used for the treatment of primary and secondary liver tumors. Various tools for the virtual planning of liver resections and ablation are available and some of them are already used clinically. Resection planes and ablation volumes can be optimized for sufficient safety margins while preserving a maximal amount of functional liver tissue. Connecting the pre-operative planning with intraoperative guidance based on the 3D imaging data would be desirable. Interactive image guided surgery enables visualization of the actual spatial location of the surgical instrument on preoperatively acquired images in real time. However, extensive soft tissue deformations during open and laparoscopic surgical and ablative procedures may occur, causing unacceptable inaccuracies. The current focus of research is the adaptation of the preoperative virtual planning models to surgery by using intraoperative imaging and biomechanical models. In contrast to open and laparoscopic surgical procedures percutaneous punctures can be performed with high accuracy under stereotactic conditions. Important prerequisites include patient immobilization, respiratory triggering and intraoperative imaging. Due to the high accuracy of probe positioning the virtual preoperative ablation plan can be precisely transferred into the real patient. A total of 350 patients with primary and secondary liver tumors have already successfully been treated with stereotactic radiofrequency ablation (SRFA). Due to its low complication rates and similar local recurrence and survival rates as compared to conventional surgery SRFA is an attractive alternative for the treatment for primary and secondary liver tumors.

[Hypopharyngeal carcinoma and red ear drum]. / Hypopharynxkarzinom und gerötetes Trommelfell.

A 46-year-old male patient with an unresectable hypopharyngeal carcinoma was treated with primary radio-chemotherapy. At follow-up, the patient presented with a red ear drum and combined hearing loss. Because of radiotherapy-induced tubal dysfunction, paracentesis was performed. Biopsy of the polypoid middle ear mucosa revealed petrous bone infiltration of hypopharyngeal carcinoma. MRI studies revealed paracarotideal tumor infiltration to the petrous bone and the middle ear arising from a cervical retropharyngeal lymph node metastasis.

[The learning curve of registration in navigated skull base surgery]. / Lernkurve bei der Registrierung navigierter Eingriffe an der Schädelbasis.

BACKGROUND: Computer aided surgery (CAS) is advantageous in challenging procedures in head and neck surgery. It is not clear, if the application of CAS has to be trained to achieve reliable results. The learning curve of the registration of the patient's coordinates to prior acquired radiologic imagery was investigated. MATERIAL AND METHODS: 4 residents performed pair-point registrations on 5 anatomic specimens in an experimental wet lab. The residents were in the same year of education and had no experience in CAS procedures. After each registration the application error was evaluated by determining the target registration error (TRE). Pair point matching by skin glued external fiducials was compared with pair point matching by internal anatomical landmarks. RESULTS: The application accuracy was improved by increasing numbers of performed registrations (p<0.001, trendtest of Page). An inverse trend of the learning curve could be observed, the median TRE values improved from 3.3 mm in the first registration to 1.6 mm after the fifth registration. In comparison e. g. an experienced CAS-user can achieve submillimetric TRE values under wet lab conditions. Pair point matching by anatomical landmarks resulted in worse application accuracy initially and the learning curve was steeper than with external fiducial markers. CONCLUSION: There is a training effect in CAS interventions. Pair point matching results in sufficient application accuracy after training only.

Integration of multimodality imaging and surgical navigation in the management of patients with refractory epilepsy. A pilot study using a new minimally invasive reference and head-fixation system.

OBJECTIVE: To review the experience with a new system (VBH system) for minimally invasive frameless stereotactic guidance, acting as a common platform to provide multimodal image integration and surgical navigation in a consecutive series of 25 patients who underwent surgery for drug-resistant seizures. METHODS: The usefulness of the VBH system for integrating all images to produce one dataset and for intraoperative instrument guidance and navigation was judged semiquantitatively in a three-tiered scale (+, ++, +++). Seizure outcome was classified according to Engel. RESULTS: The presurgical evaluation extended over 21.2 months (mean). A total of 141 registrations of images were performed (mean 5.6 per patient, range: 2 to 16). In 19 (76%) of 25 patients structural data fused with functional data were used for the presurgical workup. Six patients proceeded directly to navigated resection. Nineteen patients (76%) underwent invasive recording, of whom 13 underwent resective surgery. In seven patients (28%) the combination of multimodal image fusion and intra-operative stereotactic guidance was judged "essential" (+++) to remove the epileptogenic zone. Integration of all images to form one dataset was "essential" (+++) for decision making in 15 and "helpful" (++) in 4 patients (overall 76% of patients). Intraoperative use of frameless neuronavigation was "essential" (+++) in ten and "helpful" (++) in all remaining patients. Eighty percent of the patients achieved satisfactory seizure outcome after 1 year. CONCLUSION: The VBH system is a safe and effective non-invasive tool for repetitive imaging, multimodal image fusion and frameless stereotactic surgical navigation in candidates for epilepsy surgery.

[Headache and hypoglossal nerve palsy]. / Kopfschmerz und Hypoglossusparese.

The symptoms of a 52-year-old male patient of the university ENT out-patient department began with sudden headaches and itching neck followed by tingling in the mouth, problems with chewing and right-sided deviation of the tongue. In addition there was a history of nicotine use. MRI revealed an intraluminal increase in signal intensity in the right internal carotid artery. Isolated hypoglossal nerve palsy without participation of other cranial nerves is rare so that when headaches simultaneously occur, a dissection of the internal carotid artery is indicated, as in the case presented here.

Long-term influence of mandibular advancement on the volume of the posterior airway in skeletal Class II-patients: a retrospective analysis.

In the past, maxillomandibular advancement has resulted in considerable improvement in the volume of the posterior airway space. The objective of the present study was to find out how mandibular advancement without maxillary involvement would affect the posterior airway space in patients with mandibular retrognathism. Cone-beam computed tomographic (CT) scans were done for 20 patients before, and six months after, mandibular advancement. Cephalometric analysis at both time points included 2-dimensional and 3-dimensional assessment of the upper airway. Eight men and 12 women presented a preoperative mean (SD) Wits value of 7.4 (1.54) mm, with an airway area of 7.11 (1.88) cm2 and a volume of 14.92 (4.46) cm3. Six months postoperatively they showed a Wits value of 2.7 (0.41) mm, an airway area of 11.33 (3.49) cm2, and a volume of 25.7 (6.10) cm3. There was a mean (range) enlargement of 59 (22-82) % of the area and 73 (29-108) % of the volume. A preoperative Wits value of 8mm or more correlated significantly with a larger increase of the posterior airway space (p=0.002). At the same time, an improvement in the Wits value of 4.5mm or more correlated significantly with an increase in volume (p=0.016). The effect of mandibular advancement on the posterior airway space was significant, and the volumetric effect seems to be even more relevant than the two-dimensional changes.

Influence of Ultra-Low-Dose and Iterative Reconstructions on the Visualization of Orbital Soft Tissues on Maxillofacial CT.

BACKGROUND AND PURPOSE: Dose reduction on CT scans for surgical planning and postoperative evaluation of midface and orbital fractures is an important concern. The purpose of this study was to evaluate the variability of various low-dose and iterative reconstruction techniques on the visualization of orbital soft tissues. MATERIALS AND METHODS: Contrast-to-noise ratios of the optic nerve and inferior rectus muscle and subjective scores of a human cadaver were calculated from CT with a reference dose protocol (CT dose index volume = 36.69 mGy) and a subsequent series of low-dose protocols (LDPs I-4: CT dose index volume = 4.18, 2.64, 0.99, and 0.53 mGy) with filtered back-projection (FBP) and adaptive statistical iterative reconstruction (ASIR)-50, ASIR-100, and model-based iterative reconstruction. The Dunn Multiple Comparison Test was used to compare each combination of protocols (α = .05). RESULTS: Compared with the reference dose protocol with FBP, the following statistically significant differences in contrast-to-noise ratios were shown (all, P ≤ .012) for the following: 1) optic nerve: LDP-I with FBP; LDP-II with FBP and ASIR-50; LDP-III with FBP, ASIR-50, and ASIR-100; and LDP-IV with FBP, ASIR-50, and ASIR-100; and 2) inferior rectus muscle: LDP-II with FBP, LDP-III with FBP and ASIR-50, and LDP-IV with FBP, ASIR-50, and ASIR-100. Model-based iterative reconstruction showed the best contrast-to-noise ratio in all images and provided similar subjective scores for LDP-II. ASIR-50 had no remarkable effect, and ASIR-100, a small effect on subjective scores. CONCLUSIONS: Compared with a reference dose protocol with FBP, model-based iterative reconstruction may show similar diagnostic visibility of orbital soft tissues at a CT dose index volume of 2.64 mGy. Low-dose technology and iterative reconstruction technology may redefine current reference dose levels in maxillofacial CT.

Comparison of Two Electromagnetic Navigation Systems For CT-Guided Punctures: A Phantom Study.

PURPOSE: We compared the targeting accuracy and reliability of two different electromagnetic navigation systems for manually guided punctures in a phantom. MATERIALS AND METHODS: CT data sets of a gelatin filled plexiglass phantom were acquired with 1, 3, and 5 mm slice thickness. After paired-point registration of the phantom, a total of 480 navigated stereotactic needle insertions were performed manually using electromagnetic guidance with two different navigation systems (Medtronic Stealth Station: AxiEM; Philips: PercuNav). A control CT was obtained to measure the target positioning error between the planned and actual needle trajectory. RESULTS: Using the Philips PercuNav, the accomplished Euclidean distances were 4.42 ±â€Š1.33 mm, 4.26 ±â€Š1.32 mm, and 4.46 ±â€Š1.56 mm at a slice thickness of 1, 3, and 5 mm, respectively. The mean lateral positional errors were 3.84 ±â€Š1.59 mm, 3.84 ±â€Š1.43 mm, and 3.81 ±â€Š1.71 mm, respectively. Using the Medtronic Stealth Station AxiEM, the Euclidean distances were 3.86 ±â€Š2.28 mm, 3.74 ±â€Š2.1 mm, and 4.81 ±â€Š2.07 mm at a slice thickness of 1, 3, and 5 mm, respectively. The mean lateral positional errors were 3.29 ±â€Š1.52 mm, 3.16 ±â€Š1.52 mm, and 3.93 ±â€Š1.68 mm, respectively. CONCLUSION: Both electromagnetic navigation devices showed excellent results regarding puncture accuracy in a phantom model. The Medtronic Stealth Station AxiEM provided more accurate results in comparison to the Philips PercuNav for CT with 3 mm slice thickness. One potential benefit of electromagnetic navigation devices is the absence of visual contact between the instrument and the sensor system. Due to possible interference with metal objects, incorrect position sensing may occur. In contrast to the phantom study, patient movement including respiration has to be compensated for in the clinical setting. KEY POINTS: • Commercially available electromagnetic navigation systems have the potential to improve the therapeutic range for CT guided percutaneous procedures by comparing the needle placement accuracy on the basis of planning CT data sets with different slice thickness. Citation Format: • Putzer D, Arco D, Schamberger B et al. Comparison of Two Electromagnetic Navigation Systems For CT-Guided Punctures: A Phantom Study. Fortschr Röntgenstr 2016; 188: 470 - 478.

Ultralow-dose computed tomography imaging for surgery of midfacial and orbital fractures using ASIR and MBIR.

The influence of dose reductions on diagnostic quality using a series of high-resolution ultralow-dose computed tomography (CT) scans for computer-assisted planning and surgery including the most recent iterative reconstruction algorithms was evaluated and compared with the fracture detectability of a standard cranial emergency protocol. A human cadaver head including the mandible was artificially prepared with midfacial and orbital fractures and scanned using a 64-multislice CT scanner. The CT dose index volume (CTDIvol) and effective doses were calculated using application software. Noise was evaluated as the standard deviation in Hounsfield units within an identical region of interest in the posterior fossa. Diagnostic quality was assessed by consensus reading of a craniomaxillofacial surgeon and radiologist. Compared with the emergency protocol at CTDIvol 35.3 mGy and effective dose 3.6 mSv, low-dose protocols down to CTDIvol 1.0 mGy and 0.1 mSv (97% dose reduction) may be sufficient for the diagnosis of dislocated craniofacial fractures. Non-dislocated fractures may be detected at CTDIvol 2.6 mGy and 0.3 mSv (93% dose reduction). Adaptive statistical iterative reconstruction (ASIR) 50 and 100 reduced average noise by 30% and 56%, and model-based iterative reconstruction (MBIR) by 93%. However, the detection rate of fractures could not be improved due to smoothing effects.

Radiologic and functional evaluation of electrode dislocation from the scala tympani to the scala vestibuli in patients with cochlear implants.

BACKGROUND AND PURPOSE: Localization of the electrode after cochlear implantation seems to have an impact on auditory outcome, and conebeam CT has emerged as a reliable method for visualizing the electrode array position within the cochlea. The aim of this retrospective study was to evaluate the frequency and clinical impact of scalar dislocation of various electrodes and surgical approaches and to evaluate its influence on auditory outcome. MATERIALS AND METHODS: This retrospective single-center study analyzed a consecutive series of 63 cochlear implantations with various straight electrodes. The placement of the electrode array was evaluated by using multiplanar reconstructed conebeam CT images. For the auditory outcome, we compared the aided hearing thresholds and the charge units of maximum comfortable loudness level at weeks 6, 12, and 24 after implantation. RESULTS: In 7.9% of the cases, the electrode array showed scalar dislocation. In all cases, the electrode array penetrated the basal membrane within 45° of the electrode insertion. All 3 cases of cochleostomy were dislocated in the first 45° segment. No hearing differences were noted, but the charge units of maximum comfortable loudness level seemed to increase with time in patients with dislocations. CONCLUSIONS: The intracochlear dislocation rate of various straight electrodes detected by conebeam CT images is relatively low. Scalar dislocation may not negatively influence the hearing threshold but may require an increase of the necessary stimulus charge and should be reported by the radiologist.

Approximation of head and neck cancer volumes in contrast enhanced CT.

BACKGROUND: Tumor volume may serve as a predictor of response to radiochemotherapy (RCT) in head and neck squamous cell carcinoma (HNSCC). Computer assisted tumor volumetry requires time-consuming slice-by-slice manual or semi-automated segmentation. We questioned how accurately primary tumor and suspect cervical lymph node (LN) volumes can be approximated by the maximum tumor diameters in three dimensions. METHODS: In contrast-enhanced diagnostic CT scans of 74 patients with incident advanced HNSCC, manual slice-by-slice segmentation volumetry of primary tumor, total- and largest suspect cervical LN served as the reference method. In the same scans, maximum orthogonal diameters were measured using the distance measurement tool in standard visualization software in axial and coronal sections. From these diameters, approximate volumes were calculated using the cubic and ellipsoid formula. A second segmentation volumetry was performed in contrast enhanced radiotherapy-planning CT scans obtained prior to primary concurrent RCT 24 days (+/- 13 days) following the initial diagnostic CT scans. Intraclass correlation coefficients and Bland-Altman analyses were used to compare results. RESULTS: Slice-by-slice manual segmentation volumetry of primary and LN volumes revealed a lognormal distribution and ranged from 0 to 86 ml and 0 to 129 ml, respectively. Volume approximations in diagnostic CT scans with the ellipsoid formula resulted in an -8 % underestimation of tumor volumes (95 % CI -14 % to -1 %; p = 0.022) and an -18 % underestimation of suspect cervical LN volumes (95 % CI -25 % to -12 %; p = 0.001). Inter rater intraclass correlation for primaries was 0.95 (95 % CI +0.92 to +0.97; p = 0.001), and intra rater intraclass correlation was 0.99 (95 % CI +0.98 to +0.99; p = 0.001). The cubic formula resulted in pronounced overestimation of primary and LN volumes. Primary tumor volumes obtained by the second segmentation volumetry in radiotherapy-planning CT scans obtained on average 24 days following the initial volumetry resulted in larger primary tumor volumes (mean bias +28 %, 95 % CI +14 % to +41 %; p = 0.001). Tumor volume increase correlated with time between the diagnostic and planning CTs (r = 0.24, p = 0.05) and was approximately 1 % per day. DISCUSSION: Ellipsoid approximations of tumor and lymph node volumes in HNSCC using maximum orthogonal diameters underestimates volumes based on segmentation in multiple slices. Due to time difference and safety margins, segmented volumes in radiotherapy-planning CT scans tend to be larger than in diagnostic CT scans. CONCLUSION: Ellipsoid approximations of tumor and lymph node volumes in HNSCC are easily available from diagnostic CT scans. Volume estimates are applicable over a wide range of tumor and LN sizes and may be useful in clinical decision-making and oncologic research.

Comparison of freehand-navigated and aiming device-navigated targeting of liver lesions.

BACKGROUND: Accurate needle placement is crucial for the success of percutaneous radiological needle interventions. We compared three guiding methods using an optical-based navigation system: freehand, using a stereotactic aiming device and active depth control, and using a stereotactic aiming device and passive depth control. METHODS: For each method, 25 punctures were performed on a non-rigid phantom. Five 1 mm metal screws were used as targets. Time requirements were recorded, and target positioning errors (TPE) were measured on control scans as the distance between needle tip and target. RESULTS: Time requirements were reduced using the aiming device and passive depth control. The Euclidian TPE was similar for each method (4.6 ± 1.2-4.9 ± 1.7 mm). However, the lateral component was significantly lower when an aiming device was used (2.3 ± 1.3-2.8 ± 1.6 mm with an aiming device vs 4.2 ± 2.0 mm without). DISCUSSION: Using an aiming device may increase the lateral accuracy of navigated needle insertion.