CT-guided Interventional Procedures Research Articles

Deep convolutional-neural-network-based metal artifact reduction for CT-guided interventional oncology procedures (MARIO).

Computed tomography (CT) is routinely used to guide cryoablation procedures. Notably, CT-guidance provides 3D localization of cryoprobes and can be used to delineate frozen tissue during ablation. However, metal-induced artifacts from ablation probes can make accurate probe placement challenging and degrade the ice ball conspicuity, which in combination could lead to undertreatment of potentially curable lesions. In this work, we propose an image-based neural network (CNN) model for metal artifact reduction for CT-guided interventional procedures. An image domain metal artifact simulation framework was developed and validated for deep-learning-based metal artifact reduction for interventional oncology (MARIO). CT scans were acquired for 19 different cryoablation probe configurations. The probe configurations varied in the number of probes and the relative orientations. A combination of intensity thresholding and masking based on maximum intensity projections (MIPs) was used to segment both the probes only and probes + artifact in each phantom image. Each of the probe and probe + artifact images were then inserted into 19 unique patient exams, in the image domain, to simulate metal artifact appearance for CT-guided interventional oncology procedures. The resulting 361 pairs of simulated image volumes were partitioned into disjoint training and test datasets of 304 and 57 volumes, respectively. From the training partition, 116600 image patches with a shape of 128×128×5 pixels were randomly extracted to be used for training data. The input images consisted of a superposition of the patient and probe + artifact images. The target images consisted of a superposition of the patient and probe only images. This dataset was used to optimize a U-Net type model. The trained model was then applied to 50 independent, previously unseen CT images obtained during renal cryoablations. Three board-certified radiologists with experience in CT-guided ablations performed a blinded review of the MARIO images. A total of 100 images (50 original, 50 MARIO processed) were assessed across different aspects of image quality on a 4-point likert-type item. Statistical analyses were performed using Wilcoxon signed-rank test for paired samples. Reader scores were significantly higher for MARIO processed images compared to the original images across all metrics (all p<0.001). The average scores of the overall image quality, iceball conspicuity, overall metal artifact, needle tip visualization, target region confidence, and worst metal artifact, needle tip visualization, iceball conspicuity, and target region confidence improved by 34.91%, 36.29%, 39.94%, 34.17%, 35.13%, and 45.70%, respectively. The proposed method of image-based metal artifact simulation can be used to train a MARIO algorithm to effectively reduce probe-related metal artifacts in CT-guided cryoablation procedures.

Comparison of Ketamine-Dexmedetomidine Combination with Fentanyl-Dexmedetomidine Combination for Procedural Sedoanalgesia during CT-Guided Interventional Radiology Procedures: A Randomized Controlled Study

Background: The quest for an ideal sedoanalgesic-combination exhibiting the triad of efficacy, safety and patient comfort has led to administration of several permutations and combinations of drugs (midazolam, fentanyl, remifentanil, dexmedetomidine, propofol, ketamine, pethidine, pentazocine). The ideal sedoanalgesic for CT-guided core-biopsy of spine, radiofrequency/microwave ablation of hepatic/pulmonary lesions, has hitherto been elusive. In the absence of any guidelines, we compared a ketamine-dexmedetomidine combination (Group-K) with fentanyl-dexmedetomidine (Group-F).&#x0D; Methods: This prospective, interventional, single-centric, parallel-armed, randomized controlled study included 60 patients (ASA physical state I-II, either gender, aged 18-75y, weighing 35-85kg), undergoing CT-guided core biopsy/radiofrequency/microwave ablation in remote location, allocated to Group-K and Group-F. Independent/paired-sample t-tests were utilized and data expressed as box-whisker plots and trendlines, p-value&lt;0.05 being statistically significant.&#x0D; Results: There was a significant difference in intraprocedural pain-scores between both groups (p-values 0.0001, 0.0011, 0.0092 and 0.0201 at 0-10mins, 10-20mins, 20-30mins and 30-40mins respectively). More patients in Group-F required rescue-analgesic with reduced interventionist-satisfaction score versus Group-K. In Group-K, mean arterial pressure and heart rate (95.1mmHg;79.6/min) increased after initial ketamine bolus, but were maintained/decreased at intervention-initiation (93.2mmHg;79.4/min) and at 10min and 30min thereafter. In Group-F, MAP and HR decreased after initial fentanyl bolus (83.5mHg;71.9/min), increased with intervention-initiation (90.1mmHg;77/min), progressively decreasing at every time-point thereafter. VAS-scores (resting; on coughing) were lower in Group-K.&#x0D; Conclusion: A ketamine-dexmedetomidine combination technique demonstrated a superior sedoanalgesic effect with reduced intra-procedural bradypnea, bradycardia, rescue-drug requirement and post-procedural complications with enhanced interventionist-satisfaction and may emerge as the ideal procedural sedoanalgesic for patients undergoing CT-guided core-biopsy, radiofrequency/microwave ablation.

CT-Guided Interventional Radiology Procedures: Review Article

CT-Guided Interventional Radiology Procedures: Review Article

Validation of a method for estimating peak skin dose from CT‐guided procedures

A method for estimating peak skin dose (PSD) from CTDIvol has been published but not validated. The objective of this study was to validate this method during CT‐guided ablation procedures. Radiochromic film was calibrated and used to measure PSD. Sixty‐eight patients were enrolled in this study, and measured PSD were collected for 46 procedures. CTDIvol stratified by axial and helical scanning was used to calculate an estimate of PSD using the method [1.2 × CTDIvol(helical) + 0.6 × CTDIvol(axial)], and both calculated PSD and total CTDIvol were compared to measured PSD using paired t‐tests on the log‐transformed data and Bland‐Altman analysis. Calculated PSD were significantly different from measured PSD (P < 0.0001, bias, 18.3%, 95% limits of agreement, −63.0% to 26.4%). Measured PSD were not significantly different from total CTDIvol (P = 0.27, bias, 3.97%, 95% limits of agreement, −51.6% to 43.7%). Considering that CTDIvol is reported on the console of all CT scanners, is not stratified by axial and helical scanning modes, and is immediately available to the operator during CT‐guided interventional procedures, it may be reasonable to use the scanner‐reported CTDIvol as an indicator of PSD during CT‐guided procedures. However, further validation is required for other models of CT scanner.

Operator\u2019s eye lens dose in computed tomography\u2013guided interventions

ObjectivesTo survey (1) operator’s eye lens doses in typical computed tomography (CT)-guided interventions, (2) correlation between dose length product (DLP) and the operator’s dose, and (3) different ways for estimating the eye lens dose in clinical settings.MethodsDoses of 16 radiologists in 164 CT-guided interventional procedures were prospectively measured during a 6-month time period upon radioprotective garments and descriptive statistical outcomes were calculated. The correlations between DLP and measured doses were surveyed.ResultsOn average, the operator’s dose at the eye level (DEL, Hp(0.07)) was 22 μSv per procedure and the personal equivalent dose Hp(10) at the collar level was 21 μSv per procedure. The mean DLP of a procedure was 320 mGy cm, where 54% resulted from the fluoroscopy, the mean exposure time being 18 s. Based on the results, the operator’s DEL could be estimated from DLP using the equation DEL (μSv) = 0.10 μSv/mGy cm × patient fluoro DLP (mGycm) (p < 0.001), and the dose at the collar level (DCL) using the equation DCL (μSv) = 0.12 μSv/mGy cm × patient fluoro DLP (mGy cm) (p < 0.001). In addition, DEL (μSv) = 0.7 × DCL (μSv).ConclusionsThe eye lens doses in CT-guided interventions are generally low even without protective equipment, and it is unlikely that the recommended annual equivalent dose limit of 20 mSv for the lens of the eye will be exceeded by conducting CT-guided interventions solely. Eye lens dose can be roughly estimated based on either DLP of the procedure or dose measured at the operator’s collar level.Key Points• Eye lens doses in CT-guided operations are generally low.• It is unlikely that the ICRP recommendation of the yearly equivalent dose limit of 20 mSv will be exceeded by conducting CT-guided interventions solely.• Magnitude of eye lens dose can be estimated based on either DLP of the procedure or dose measured at the operator’s collar level.

Development of a Gripper with Variable Stiffness for a CT-Guided Needle Insertion Robot

In recent years, interventional radiology (IR) as a medical procedure has attracted considerable attention. Among the various IR techniques, computed tomography (CT)-guided IR is performed by inserting a specific needle into a lesion under CT guidance, leading to this medical procedure being less invasive. However, as the procedure requires the doctor to be positioned near the CT, radiation exposure may be a major concern. To overcome this problem, we developed a remote-controlled robotic system for needle insertion during CT-guided interventional procedures. The current needle holder for the robot is risky in that it might hurt a patient since a needle is always held firmly even when the patient moves. To solve this problem, we designed and fabricated a gripper with variable stiffness through jamming transition. Subsequently, we conducted experiments to investigate the effect of elements constituting the gripper to improve its performance.

03:54 PM Abstract No. 369 Comparison of measured peak skin dose to scanner-reported dose indices during CT-guided interventions

CT-guided interventional procedures, in particular ablations and complex orthopedic procedures, can at times require the use of substantial radiation doses. A theoretical model for skin dose based on the definitions of CTDIvol and CTIDw has been published, but not validated experimentally. The aim of this study was to validate this model and benchmark against a typical mix of helical and axial scanning during CT-guided procedures. 68 patients were enrolled in this IRB-approved study. Radiochromic film was calibrated using standard methods and used to measure patient skin doses for consecutive ablation procedures performed on a single CT scanner. Procedural dose indices, including CTDIvol, were collected and compared to the measured skin doses using a paired t-test and Bland-Altman analysis. CTDIvol separated by axial and helical imaging was used to estimate skin doses using a published theoretical model, which were compared to measured doses. All data was log transformed for hypothesis testing. When a theoretical model was applied to the data, predicted skin doses were significantly different from measured skin doses according to a two-tailed t-test (p < 0.0001). However, skin dose was not significantly different from uncorrected total CTDIvol according to a two-tailed t-test (p = 0.29). Bland-Altman analysis revealed a bias of -3.75 for percent difference (standard deviation [SD] = 24.0) with limits of agreement (LoA) of [-50.7, 43.2] between measured skin dose and CTDIvol (measured skin dose – CTDIvol) and a bias of -18.1 (SD = 22.4) with LoA of [-62.0, 25.7] between measured skin dose and skin dose as calculated using a theoretical model. CTDIvol alone was a better predictor of skin dose than dose estimated using a theoretical model. This is likely a consequence of how CTDI is measured, with scatter contributing much of the signal, rather than primary radiation. Also, patient positioning during CT-guided procedures varies substantially, and patients are often off-center, meaning the skin surface may not match well to the surface of a phantom centered in the gantry. CTDIvol is reported by all CT scanners and is a simple index for monitoring skin dose.

Operator radiation doses during CT-guided spine procedures

ObjectivesTo perform a pilot study to quantify the radiation dose incident on operators during CT-guided interventional spine procedures, and provide a quick method to approximate it based on the total amount of radiation reported by the CT scanner. Patients and MethodsData retrospectively obtained from 26 consecutive CT-guided spine procedures, encompassing a variety of interventions. Intermittent low-dose limited-coverage CT-scanning performed using a "step and shoot" mode to visualize needle advancement. The operator wore an electronic direct dosimeter to record the dose measured above the operator's lead apron [μGy] for each procedure. Total amount of radiation used for CT-guidance quantified by the Dose-Length Product (DLP) [mGy-cm] provided by the CT scanner. The relationship between the operator's dose and the DLP was assessed. ResultsAverage and median operator's dose were 2.3 and 1.9 μGy, respectively, with half of these values ranging between 0.7 and 2.5 μGy. Average and median DLP values used to perform the CT-guided procedure were 58 and 54 mGy-cm respectively, and half of these values ranged between 38 and 68 mGy-cm. There was a statistically significant correlation between the operator's dose and the DLP used to perform CT-guidance (r = 0.61), with an operator's dose-DLP conversion factor of 0.04 μGy / 1 mGy-cm (range: 0.006-0.083 μGy / 1 mGy-cm). ConclusionsIn our series, the average amount of radiation used during CT guided procedures was about 50 mGy-cm (DLP), and the corresponding average operator's dose was about 2 μGy. We showed how an approximate estimate of the operator's dose could be obtained right after each procedure, based on the CT-scanner DLP output.

Procedure-specific CT Dose and Utilization Factors for CT-guided Interventional Procedures.

Purpose To present procedure-specific radiation dose metric distributions and define quantitative CT utilization factors for CT-guided interventional procedures. Materials and Methods This single-center, retrospective study collected dictation reports and radiation dose data from 9143 consecutive CT-guided interventional procedures in adult patients from 2012 to 2017. Procedures were sorted into four major interventional categories: ablation, aspiration, biopsy, and drainage, each of which was further divided into subcategories. After exclusion, a total of 8213 procedures (4391 in men and 3822 in women) were divided into 21 subcategories. The mean patient age at examination for men was 62 years ± 15 (standard deviation; age range, 19-114 years), and for women it was 61 years ± 15 (age range, 19-113 years). Distributions of dose metrics and CT usage-related parameters were analyzed by category with descriptive statistic outcomes. Quantitative CT utilization factors (which measure average CT usage) for each interventional subcategory were derived by using total scan length, acquisition count, and number of images. Results Interventional CT scans have distinctly different dose metric characteristics from diagnostic CT scans. Wide variations of dose metrics were observed among subcategories, even within the same major category. For the most frequently performed CT-guided interventional procedures within each major category, liver ablation, chest aspiration, liver biopsy, and single abdominal drainage, the median dose-length product was 2351, 657, 1175, and 1125 mGy ∙ cm, respectively. Procedure-specific CT utilization factors ranged between 0.6 and 3.6. Conclusion This study provides procedure-specific CT dose metric distributions and quantitative CT utilization factors on the basis of a large number of procedures and categorization of CT-guided interventional procedures. © RSNA, 2018.

Radiation exposure during CT-guided biopsies: recent CT machines provide markedly lower doses.

To examine radiation dose levels of CT-guided interventional procedures of chest, abdomen, spine and extremities on different CT-scanner generations at a large multicentre institute. 1,219 CT-guided interventional biopsies of different organ regions ((A) abdomen (n=516), (B) chest (n=528), (C) spine (n=134) and (D) extremities (n=41)) on different CT-scanners ((I) SOMATOM-Definition-AS+, (II) Volume-Zoom, (III) Emotion6) were included from 2013-2016. Important CT-parameters and standard dose-descriptors were retrospectively examined. Additionally, effective dose and organ doses were calculated using Monte-Carlo simulation, following ICRP103. Overall, radiation doses for CT interventions are highly dependent on CT-scanner generation: the newer the CT scanner, the lower the radiation dose imparted to patients. Mean effective doses for each of four procedures on available scanners are: (A) (I) 9.3mSv versus (II) 13.9mSv (B) (I) 7.3mSv versus (III) 11.4mSv (C) (I) 6.3mSv versus (II) 7.4mSv (D) (I) 4.3mSv versus (II) 10.8mSv. Standard dose descriptors [standard deviation (SD); CT dose indexvol (CTDIvol); dose-length product (DLPbody); size-specific dose estimate (SSDE)] were also compared. Effective dose, organ doses and SSDE for various CT-guided interventional biopsies on different CT-scanner generations following recommendations of the ICRP103 are provided. New CT-scanner generations involve markedly lower radiation doses versus older devices. • Effective dose, organ dose and SSDE are provided for CT-guided interventional examinations. • These data allow identifying organs at risk of higher radiation dose. • Detailed knowledge of radiation dose may contribute to a better individual risk-stratification. • New CT-scanner generations involve markedly lower radiation doses compared to older devices.

3:45 PM Abstract No. 76 Procedure-specific complexity factors based on dose metric distributions for CT-guided interventional procedures

3:45 PM Abstract No. 76 Procedure-specific complexity factors based on dose metric distributions for CT-guided interventional procedures

Evaluation of the clinical benefit of an electromagnetic navigation system for CT-guided interventional radiology procedures in the thoraco-abdominal region compared with conventional CT guidance (CTNAV II): study protocol for a randomised controlled trial

BackgroundInterventional radiology includes a range of minimally invasive image-guided diagnostic and therapeutic procedures that have become routine clinical practice. Each procedure involves a percutaneous needle insertion, often guided using computed tomography (CT) because of its availability and usability. However, procedures remain complicated, in particular when an obstacle must be avoided, meaning that an oblique trajectory is required. Navigation systems track the operator’s instruments, meaning the position and progression of the instruments are visualised in real time on the patient’s images. A novel electromagnetic navigation system for CT-guided interventional procedures (IMACTIS-CT®) has been developed, and a previous clinical trial demonstrated improved needle placement accuracy in navigation-assisted procedures. In the present trial, we are evaluating the clinical benefit of the navigation system during the needle insertion step of CT-guided procedures in the thoraco-abdominal region.Methods/designThis study is designed as an open, multicentre, prospective, randomised, controlled interventional clinical trial and is structured as a standard two-arm, parallel-design, individually randomised trial. A maximum of 500 patients will be enrolled. In the experimental arm (navigation system), the procedures are carried out using navigation assistance, and in the active comparator arm (CT), the procedures are carried out with conventional CT guidance. The randomisation is stratified by centre and by the expected difficulty of the procedure. The primary outcome of the trial is a combined criterion to assess the safety (number of serious adverse events), efficacy (number of targets reached) and performance (number of control scans acquired) of navigation-assisted, CT-guided procedures as evaluated by a blinded radiologist and confirmed by an expert committee in case of discordance. The secondary outcomes are (1) the duration of the procedure, (2) the satisfaction of the operator and (3) the irradiation dose delivered, with (4) subgroup analysis according to the expected difficulty of the procedure, as well as an evaluation of (5) the usability of the device.DiscussionThis trial addresses the lack of published high-level evidence studies in which navigation-assisted CT-guided interventional procedures are evaluated. This trial is important because it addresses the problems associated with conventional CT guidance and is particularly relevant because the number of interventional radiology procedures carried out in routine clinical practice is increasing.Trial registrationClinicalTrials.gov identifier: NCT01896219. Registered on 5 July 2013.

Application of Real-Time 3D Navigation System in CT-Guided Percutaneous Interventional Procedures: A Feasibility Study.

Introduction To evaluate the accuracy of a quantitative 3D navigation system for CT-guided interventional procedures in a two-part study. Materials and Methods Twenty-two procedures were performed in abdominal and thoracic phantoms. Accuracies of the 3D anatomy map registration and navigation were evaluated. Time used for the navigated procedures was recorded. In the IRB approved clinical evaluation, 21 patients scheduled for CT-guided thoracic and hepatic biopsy and ablations were recruited. CT-guided procedures were performed without following the 3D navigation display. Accuracy of navigation as well as workflow fitness of the system was evaluated. Results In phantoms, the average 3D anatomy map registration error was 1.79 mm. The average navigated needle placement accuracy for one-pass and two-pass procedures, respectively, was 2.0 ± 0.7 mm and 2.8 ± 1.1 mm in the liver and 2.7 ± 1.7 mm and 3.0 ± 1.4 mm in the lung. The average accuracy of the 3D navigation system in human subjects was 4.6 mm ± 3.1 for all procedures. The system fits the existing workflow of CT-guided interventions with minimum impact. Conclusion A 3D navigation system can be performed along the existing workflow and has the potential to navigate precision needle placement in CT-guided interventional procedures.

Potential Clinical Ramifications of Dose Alert on CT-Guided Interventional Procedures

INTRODUCTION In an effort to protect patients from inadvertent radiation overexposure during CT exams, a new feature, called “dose check,” has been implemented by all CT scanner manufacturers [1-3]. Dose check is designed in accordance with the National Electrical Manufacturers Association (NEMA) XR-25 national standard [4]. Dose check initiates a procedural pause during the examination to indicate that the prescribed image acquisition may yield an “abnormally” large dose to the patient; the upper limit of “normal” patient dose values (threshold CT dose index [CTDIvol] or dose length product [DLP] values) are predetermined by the institution. These thresholds are referred to as “notification values” and “alert values.” Dose check is comprised of two components: dose notification and dose alert. Through dose notification, the estimated CTDIvol or DLP value from each acquisition is compared with the notification value. If the estimated CTDIvol or DLP exceeds the notification value, the technologist is notified, questioned if the acquisition(s) should continue as prescribed, and prompted to record justification for the unusually large CTDIvol or DLP value. The notification value can be configured by the institution and set for each individual scan acquisition. Through dose alert, the cumulative

Reduced Kilovoltage in Computed Tomography–Guided Intervention in a Community Hospital: Effect on the Radiation Dose

PurposeThe purpose of this study was to determine whether low-kilovoltage (80 or 100 kV) computed tomography (CT)-guided interventions performed in a community-based hospital are feasible and to compare radiation exposure incurred with conventional 120 kV potential. Materials and MethodsEffective doses (ED) received by patients who underwent CT-guided intervention were analysed before and after a low-dose kilovoltage protocol was instituted in our department. We performed CT-guided procedures of 93 consecutive patients by using conventional 120-kV tube voltage (50 patients) and a low voltage of 80 or 100 kV for the remainder of this cohort. Automatic tube current modulation was enabled to obtain the best image quality. Procedure details were prospectively recorded and included examination site and type, slice width, tube voltage and current, dose length product, volume CT dose index, and size-specific dose estimate. Dose length product was converted to ED to account for radiosensitivity of specific organs. Statistical comparisons with test differences in the ED, volume CT dose index, size-specific dose estimate, and effective diameter (patient size) were made by using the Student t test. ResultsAll but 6 of the procedures performed at 80 kV were successful, for a success rate of 86%. At lower voltages, the ED was significantly (P < .01) reduced, on average, by 57%, 73%, and 65% for the pelvic, chest, and abdomen procedures, respectively. ConclusionA low-dose radiation technique by using 80 or 100 kV results in a high technical success rate for pelvic, chest, and abdomen CT-guided interventional procedures, although dramatically decreasing radiation exposure. There was no significant difference in effective diameter (patient size) between the conventional and the low-dose groups, which would suggest that dose reduction was indeed a result of kVp change and not patient size.

Radiation Dose Optimization for CT-Guided Interventional Procedures in the Abdomen and Pelvis

Radiation dose to patients can be high for some CT-guided interventional procedures in the abdomen and pelvis, especially tumor ablations. Strategies for radiation dose reduction include choosing an alternative guidance modality that does not use radiation whenever feasible, restricting the cranio-caudal length of interventional scans to the interventional target, and refinement of technical skills in order to minimize the number of scans acquired for interventional guidance. Dose optimization for these procedures is best achieved by lowering the tube current relative to the prior diagnostic scan, choosing dose efficient scanning modes, and using intermittent-mode, narrowly collimated CT fluoroscopy for interventional guidance.

Gold Nanoparticles Provide Bright Long-Lasting Vascular Contrast for CT Imaging

Iodinated contrast agent for CT has a short half-life in the vasculature. As the field of interventional procedures expands, a more durable contrast agent would be highly useful. Our study investigated whether gold nanoparticles are feasible as a long-lasting vascular contrast agent for CT. Gold nanoparticles were synthesized by a modified Turkevich method, coated with methoxy-polyethylene glycol-thiol chains, and compared with an iodine-based contrast agent used in mice. Contrast agents were imaged in tubes by CT at 40, 60, and 140 kVp and then were tested in vivo by tail vein injection. Nine mice received gold nanoparticles, two received iodine-based contrast agent, and one received saline. CT of mice was performed at 60 kVp immediately, 6 hours, and 24 hours after injection. In an isolated form in tubes, gold nanoparticles had greater radiographic density than did iodine-based contrast agent at 40 kVp and were comparable at the other CT voltages. In mice, gold nanoparticles provided bright contrast enhancement that enabled clear visualization of the abdominal aorta and renal arteries, which could not be distinguished without contrast agent. This persisted up to 24 hours, which was the last time point assessed. Contrast enhancement of the vasculature by iodine-based contrast agent was present immediately after injection but had disappeared by 6 hours. Gold nanoparticles can provide clear and durable contrast enhancement of the vasculature even at 24 hours. These findings merit further study of gold nanoparticles for their potential as a contrast agent in CT and CT-guided interventional procedures.

Assessment of Patient and Occupational Dose in Established and New Applications of MDCT Fluoroscopy

This study aimed to assess patient dose and occupational dose in established and new applications of MDCT fluoroscopy. Electronic personal dosimeters were used to measure occupational dose equivalent. Effective patient dose was derived from the recorded dose-length product. Acquisition parameters that were observed during CT fluoroscopy (CTF) provided the basis for the estimation of an entrance skin dose profile. Two hundred ten CT-guided interventional procedures were included in the study. The median effective patient dose was 10 mSv (range, 0.1-235 mSv; 107 procedures). The median peak entrance skin dose was 0.4 Sv (0.1-2.1 Sv; 27 procedures). From 547 measurements of occupational dose equivalent, a median occupational effective dose of 3 muSv per procedure was derived for the interventional radiologists and 0.4 muSv per procedure for the assisting radiologists and radiology technologists. The estimated maximum occupational effective dose reached 0.4 mSv. The study revealed high effective patient doses, up to 235 mSv, mainly for relatively new applications such as CTF-guided radiofrequency ablations using MDCT, vertebroplasty, and percutaneous ethanol injections of tumors. Entrance doses were occasionally in the range of the warning level for deterministic skin effects but were always below the threshold for serious deterministic effects. The complexity of the procedure, expected benefits of the treatment, and general health state of the patient contribute to the justification of observed high effective patient doses.

Comparison of Measured and Calculated Skin Doses in CT-Guided Interventional Procedures

The objective of our study was to compare theoretic estimations of the dose to the patient's skin during CT-guided interventional procedures with measurements performed using radiation therapy verification films. In each of the 12 interventions studied, a Kodak EDR2 film was positioned under the patient's anatomic area of concern. After processing, each film was scanned with a medical-grade scanner to produce a digital image from which the gray-scale profiles were obtained using the appropriate software. From these data and respective data from a series of calibration films, the entrance skin dose (ESD) profiles were derived. These ESD profiles were compared with the ESD profiles produced using a theoretic model and its revised version, which utilizes the DICOM data of each slice (i.e., tube potential, tube loading, slice thickness, slice location, pitch, and table height) and air-kerma output measurements from the CT tube. In general, the ESD profiles calculated using the revised theoretic method were in better agreement with the profiles derived from the verification films than the ESD profiles derived from the original theoretic method. The deviations from the peak skin doses (PSDs) derived from the digital film images were within -3% and 27% of the PSDs derived from the verification films. The respective deviations of the ESD profiles calculated with the original theoretic method were quite larger. The theoretic model provides a useful tool for estimating skin doses during CT-guided interventions with a reasonable level of accuracy. With further refinement and a little automation this method could be implemented for daily use.

Computergestütztes Navigationssystem für CT-gesteuerte Interventionen: Ergebnisse am Phantom und im klinischen Einsatz

To evaluate the technical applicability and accuracy of a navigation system for CT-guided interventional procedures in a phantom and a patient study. A novel navigation tool (CAPPA IRAD, CAS innovations AG, Erlangen, Germany) was employed for CT-guided biopsies in a phantom and in patients. The entire system consists of a PC, navigation software, an optical tracking system and a patient frame. For the phantom study, a spine phantom in wax was used. The phantom as well as the patients were placed on the CT table in a stable position and fixed within a double vacuum device. The patient frame equipped with optical and CT markers was placed above the target region, followed by acquisition of a planning scan. All data were transferred to the navigation system inside the scanning room, and with the aid of the above mentioned navigation software, the biopsy pathway was planned. Hereafter, the needle holder was aligned accordingly, and a coaxial biopsy needle was pushed forward to the planned target. An additional control scan confirmed needle position, and the navigation software was used to evaluate the distance between the target and needle tip. In the phantom study (n = 60) the average deviation between the planned and documented needle tip position was 1.1 mm. In the clinical study (n = 15), we performed biopsies of the lung, the mediastinal area, the pancreas and liver and some bone biopsies as well as a therapeutic nerve root infiltration. 12 of 15 cases required oblique needle access. In 9 / 15 cases merely a single planning and control scan were required, whereas in 5 / 15 cases additional safety or correction scans were performed. In the case of pancreas biopsy, the lesion (diameter 1 centimeter) visible during the arterial phase only could not be punctured even following repeated corrections due to severe breathing artifacts and pronounced peristaltic movement of the adjacent bowel. The time between planning CT and correct needle position was about 30 minutes. The navigation system allows for safe interventions in case of angulated needle access with high accuracy and little tissue trauma. However, insufficient corrections for respiration movement constitute a substantial limitation of the tool.