A method for calculating the dose length product from CT DICOM images

Radiation doses and diagnostic reference levels for common CT scans in adults in Northwest region of Iran

This study aims to estimate organ dose and cancer risks, establish region-specific diagnostic reference levels (DRLs), and determine achievable doses (ADs) for common CT procedures in adults in the northwest of Iran. Effective and organ doses were estimated using VirtualDoseCT software in a sample of 480 adult patients who underwent head, sinus, chest, and abdomen-pelvis (AP) CT scans. The guidelines provided by the BEIR VII report were utilized to estimate cancer risks. Effective and organ doses for specific procedures were determined, with the highest mean organ dose being observed in the brain during head CT examinations, with a value of 54.02 mGy. It was observed that the lungs in chest examinations and the colon in AP examinations had the highest risk of cancer, with rates of 30.72 and 21.37 per 100,000 persons, respectively. Higher cancer risk values were generally exhibited by females compared to males. The DRLs for common CT examinations were established as follows: Head CT (CTDIvol 41 mGy, DLP 760 mGy cm), Sinus CT (CTDIvol 16 mGy, DLP 261 mGy cm), Chest CT (CTDIvol 8 mGy, DLP 287 mGy cm), and AP CT (CTDIvol 9 mGy, DLP 508 mGy cm). Significant variations in dose distribution among facilities were identified, indicating the need for optimization. The study highlights the importance of minimizing radiation exposure to critical organs and promoting patient safety in CT examinations. The establishment of region-specific DRLs and ADs can help optimize radiation doses and reduce cancer risks for patients.

The impact of automatic tube current modulation related settings of a modern GE CT scanner on image quality and patient dose; details do matter

PURPOSE

To investigate the operation principles of the automatic tube current modulation (ATCM) of a modern GE healthcare CT scanner, and the impact of related settings on image quality and patient dose.

MATERIAL & METHODS

A dedicated phantom (Mercury 4.0) was scanned using two of the most frequently used clinical scanning protocols (chest and abdomen-pelvis). The preset protocol settings were used as starting points (reference conditions). Scan direction, scan mode (helical vs. axial), total beam width, tube potential (kVp), and ATCM settings were then modified individually to understand their impact on radiation dose and image quality. Regarding the ATCM settings, the SmartmA minimum and maximum mA limits, and the noise index (NI) values were varied. As surrogates of patient dose, the CTDIvol and DLP values of each scan were used. As surrogates of image quality were used the image noise and the detectability index (d') of five different materials (air, solid water, polystyrene, iodine, and bone) embedded in the Mercury phantom calculated with the ImQuest software.

RESULTS

The scanning direction did not have any effect on ATCM curves, unlike what has been observed in CT scanners from other manufacturers. Total beam width does matter, however, the SmartmA limit settings and kVp selection had the greatest impact on image quality and dose. It was seen that improper minimum mA limit settings practically invalidated the ATCM operation. In contrast, when full modulation was allowed without restrictions, noise standard deviation, and detectability index became much more consistent across the wide range of phantom diameters. For lower kVp settings an impressive dose reduction was observed that requires further investigation.

CONCLUSION

SmartmA is a tool that if not properly used may increase the patient doses considerably. Therefore, its settings should be carefully adjusted for each preset different clinical protocol.

Automatic image quality evaluation in digital radiography using for-processing and for-presentation images

PURPOSE

To investigate the impact of digital image post-processing algorithms on various image quality (IQ) metrics of radiographic images under different exposure conditions.

METHODS

A custom-made phantom constructed according to the instructions given in the IAEA Human Health Series No.39 publication was used, along with the respective software that automatically calculates various IQ metrics. Images with various exposure parameters were acquired with a digital radiography unit, which for each acquisition produces two images: one for-processing (raw) and one for-presentation (clinical). Various examination protocols were used, which incorporate diverse post-processing algorithms. The IQ metrics' values (IQ-scores) obtained were analyzed to investigate the effects of increasing incident air kerma (IAK) on the image receptor, tube potential (kVp), additional filtration, and examination protocol on image quality, and the differences between image type (raw or clinical).

RESULTS

The IQ-scores were consistent for repeated identical exposures for both raw and clinical images. The effect that changes in exposure parameters and examination protocol had on IQ-scores were different depending on the IQ metric and image type. The expected positive effect that increasing IAK and decreasing tube potential should have on IQ was clearly exhibited in two IQ metrics only, the signal difference-to-noise-ratio (SDNR) and the detectability index (d'), for both image types. No effect of additional filtration on any of the IQ metrics was detected on images of either type. An interesting finding of the study was that for all different image acquisition selections the d' scores were larger in raw images, whereas the other IQ metrics were larger in clinical images for most of the cases.

CONCLUSIONS

Since IQ-scores of raw and their respective clinical images may be largely different, the same type of image should be consistently used for monitoring IQ constancy and when results from different X-ray systems are compared.

DIAGNOSTIC REFERENCE LEVELS FOR COMMON CT EXAMINATIONS: RESULTS FROM A STATEWIDE DOSE SURVEY

The aim of this study was to investigate the current radiation doses for CT examinations throughout a state in Malaysia and, based on this data, to propose local diagnostic reference levels (DRLs) for the most common CT examinations. A study was conducted in three of the four hospitals that have provided CT services throughout the state. A survey booklet was designed to facilitate collection of pertinent CT scan data. The following information were extracted and recorded for each study: tube voltage, tube current, number of scans phases, CT dose index volume (CTDIvol) and dose length product (DLP). Proposed local DRLs of CT brain and thorax were up to 12% lower than the current national DRLs. However, an increase of DLP (median value) for CT abdomen was also found as compared to the 75th percentile of national DRLs. Therefore, considerable optimisation should be made to achieve a better dose reduction.

Image Quality Comparison between Digital Breast Tomosynthesis Images and 2D Mammographic Images Using the CDMAM Test Object

To evaluate the image quality (IQ) of synthesized two-dimensional (s2D) and tomographic layer (TL) mammographic images in comparison to the 2D digital mammographic images produced with a new digital breast tomosynthesis (DBT) system. Methods: The CDMAM test object was used for IQ evaluation of actual 2D images, s2D and TL images, acquired using all available acquisition modes. Evaluation was performed automatically using the commercial software that accompanied CDMAM. Results: The IQ scores of the TLs with the in-focus CDMAM were comparable, although usually inferior to those of 2D images acquired with the same acquisition mode, and better than the respective s2D images. The IQ results of TLs satisfied the EUREF limits applicable to 2D images, whereas for s2D images this was not the case. The use of high-dose mode (H-mode), instead of normal-dose mode (N-mode), increased the image quality of both TL and s2D images, especially when the standard mode (ST) was used. Although the high-resolution (HR) mode produced TL images of similar or better image quality compared to ST mode, HR s2D images were clearly inferior to ST s2D images. Conclusions: s2D images present inferior image quality compared to 2D and TL images. The HR mode produces TL images and s2D images with half the pixel size and requires a 25% increase in average glandular dose (AGD). Despite that, IQ evaluation results with CDMAM are in favor of HR resolution mode only for TL images and mainly for smaller-sized details.

Evaluation of automatic tube current modulation of CT scanners using a dedicated and the CTDI dosimetry phantoms

PURPOSE

To investigate the operation principles of the automatic tube current modulation (ATCM) of a CT scanner, using a dedicated phantom and the CT dosimetry index (CTDI) phantom.

MATERIAL AND METHODS

The Mercury 4.0 phantom and three different configurations of the CTDI dosimetry phantom were employed. A frequently used clinical scanning protocol was employed as a basis for the acquisitions performed with all phantoms, using both scanning directions. Additional acquisitions with different pitch and examination protocols were performed with Mercury phantom, to further explore their effect on ATCM and the resulting image quality. Different software named DICOM Info Extractor, ImageJ, and imQuest, were used to derive CTDI_vol and table position, image noise, and water equivalent diameter (WED) of each phantom CT image, respectively. ImQuest was also used to derive the detectability index (d') of five different materials (air, solid water, polystyrene, iodine, and bone) embedded in the Mercury phantom.

RESULTS

It was exhibited with all four phantoms that the scanning direction greatly affects the modulation curves. The fitting of the dose modulations curves suggested that for each table position what determines the CTDI_vol value is the WED values of the phantom structures laying ahead towards the scanning direction, for a length equal to the effective width of the X-ray beam. Furthermore, it was also exhibited that ATCM does not fully compensate for larger thicknesses, since images of larger WED phantom sections present more noise (larger SD) in all four phantoms and in Mercury 4.0 phantom smaller detectability (d').

CONCLUSION

Mercury 4.0 is a dedicated phantom for a complete and in-depth evaluation of the ATCM operation and the resulting image quality. However, in its absence, different CTDI configurations can be used as an alternative to investigate and comprehend some basic operation principles of the CT scanners' ATCM systems.

Evaluation of Radiation Exposure to the Patients Undergoing Positron Emission Tomography/Computed Tomography-Guided Biopsies

Purpose

We aimed to evaluate the radiation exposure to patients undergoing positron emission tomography/computed tomography (PET/CT)-guided biopsies.

Materials and Methods

Patients undergoing PET/CT-guided biopsy were recruited prospectively from October 2019 to April 2020. PET/CT-guided biopsy from a tracer avid site was done using an automated-robotic-arm 1 h after intravenous injection of F-18-fluorodeoxyglucose (FDG) (2-5 mCi) or Ga-68-PSMA (1-4 mCi). Regional CT-images were acquired for biopsy planning and confirmation of needle placement. The internal radiation exposure due to the PET component was estimated using the value of activity injected and dose-coefficient for FDG and PSMA. The external radiation exposure due to the CT component was estimated using the value of dose length product and organ coefficients conversion factor. The total effective dose during the procedure was calculated by adding exposure due to both CT and PET components. Percentage contribution from CT and PET component to total effective dose was compared using a paired t-test.

Results

A total of 101 patients (76 males) were recruited for PET/CT-guided biopsy using FDG (n = 79) and PSMA (n = 22). The mean effective-dose due to PET and CT components and total effective-dose was 2.49 ± 1.02 mSv, 2.35 ± 1.03 mSv and 4.83 ± 1.90 mSv, respectively, for FDG-guided procedures and 1.60 ± 0.57 mSv, 3.06 ± 1.36 mSv, and 4.66 ± 1.37 mSv for Ga-68-PSMA-guided procedures. The percentage contribution of PET and CT in total effective-dose was comparable in F-18-FDG and Ga-68-PSMA PET/CT-guided biopsy procedures; however, for Ga-68-PSMA PET/CT-biopsies, CT contributed a higher radiation dose than PET component.

Conclusion

PET/CT-guided biopsy is a safe interventional procedure, and radiation exposure to the patients was less than routine whole-body PET/CT-imaging.

Evaluation of image quality and patient exposure in fluoroscopy using a phantom: Is there any clinical relevance?

OBJECTIVE

To investigate the impact of X-ray preset acquisition protocol settings on fluoroscopy image quality (IQ) and radiation exposure.

MATERIALS & METHODS

A quality control (QC) phantom was imaged with a modern digital C-arm system, using various preset fluoroscopy protocols. IQ was assessed using human observers and in-house software for automated evaluation, based on contrast-to-noise ratios of details and their background. Patient radiation exposure was evaluated using the displayed Incident Air-Kerma and Kerma-Area Product values.

RESULTS

Protocol selection affects radiation exposure by a factor of about 3. IQ evaluation showed that acquisition protocols produce images with quite different characteristics. The visual IQ evaluation method was time consuming and cumbersome. The automated method, utilized the visual IQ evaluation results for calibration of detection thresholds. However, it failed to reproduce these results for all images and details types. In some images, digital image processing created artifacts which affected the pixel value distributions around details in a way that could be handled only by the human vision.

CONCLUSION

Manufacturers provide many preset protocols designated for specific clinical uses, which have large impact on IQ characteristics and radiation exposure. However, protocol settings' selection rationale is essentially a "black box" for the end user. Though QC phantoms are currently used for IQ evaluation, they are not appropriate for drawing firm conclusions concerning the expected performance of each protocol in clinical practice. Currently, there is no consensus on the optimum technical characteristics of preset protocols for specific procedures. More work is needed in this area.

Task-based assessment of neck CT protocols using patient-mimicking phantoms-effects of protocol parameters on dose and diagnostic performance

Objectives

To assess how modifying multiple protocol parameters affects the dose and diagnostic performance of a neck CT protocol using patient-mimicking phantoms and task-based methods.

Methods

Six patient-mimicking neck phantoms containing hypodense lesions of 1 cm diameter and 30 HU contrast and one non-lesion phantom were examined with 36 CT protocols. All possible combinations of the following parameters were investigated: 100- and 120-kVp tube voltage; tube current modulation (TCM) noise levels of SD 7.5, 10, and 14; pitches of 0.637, 0.813, and 1.388; filtered back projection (FBP); and iterative reconstruction (AIDR 3D). Dose-length products (DLPs) and lesion detectability (assessed by 14 radiologists) were compared with the clinical standard protocol (120 kVp, TCM SD 7.5, 0.813 pitch, AIDR 3D).

Results

The DLP of the standard protocol was 25 mGy•cm; the area under the curve (AUC) was 0.839 (95%CI: 0.790–0.888). Combined effects of tube voltage reduction to 100 kVp and TCM noise level increase to SD 10 optimized protocol performance by improving dose (7.3 mGy•cm) and detectability (AUC 0.884, 95%CI: 0.844–0.924). Diagnostic performance was significantly affected by the TCM noise level at 120 kVp (AUC 0.821 at TCM SD 7.5 vs. 0.776 at TCM SD 14, p = 0.003), but not at 100-kVp tube voltage (AUC 0.839 at TCM SD 7.5 vs. 0.819 at TCM SD 14, p = 0.354), the reconstruction method at 100 kVp (AUC 0.854 for AIDR 3D vs. 0.806 for FBP, p < 0.001), but not at 120-kVp tube voltage (AUC 0.795 for AIDR 3D vs. 0.793 for FBP, p = 0.822), and the tube voltage for AIDR 3D reconstruction (p < 0.001), but not for FBP (p = 0.226).

Conclusions

Combined effects of 100-kVp tube voltage, TCM noise level of SD 10, a pitch of 0.813, and AIDR 3D resulted in an optimal neck protocol in terms of dose and diagnostic performance. Protocol parameters were subject to complex interactions, which created opportunities for protocol improvement.

Key Points

• A task-based approach using patient-mimicking phantoms was employed to optimize a CT system for neck imaging through systematic testing of protocol parameters.

• Combined effects of 100-kVp tube voltage, TCM noise level of SD 10, a pitch of 0.813, and AIDR 3D reconstruction resulted in an optimal protocol in terms of dose and diagnostic performance.

• Interactions of protocol parameters affect diagnostic performance and should be considered when optimizing CT techniques.

Electronic supplementary material

The online version of this article (10.1007/s00330-020-07374-8) contains supplementary material, which is available to authorized users.

3D imaging and stealth navigation instead of CT guidance for radiofrequency ablation of osteoid osteomas: a series of 52 patients

Background

Osteoid osteomas are benign bone neoplasms that may cause severe pain and limit function. They are commonly treated by radiofrequency ablation (RFA) through a needle inserted into the nidus of the lesion under CT guidance, which is associated with exposure of young patients to relatively high dose of radiation. The objective of this study was to investigate the amount of radiation, effectiveness and safety of an alternative imaging approach, the 3D image-guided (O-arm) technology and the Stealth navigation.

Methods

We retrospectively reviewed 52 electronic medical files of patients (mean age 24.7 years, range 8–59 years) who were treated with thermal ablation of benign osteoid osteomas guided by the navigated O-arm-assisted technique in our institution between 2015 and 2017. Data were extracted on the associated complications, the reduction in pain at 3 months and one year postoperatively, and the amount of radiation administered during the procedure.

Results

The level of pain on a visual analogue scale decreased from the preoperative average of 7.73 to 0 at the 3-month follow-up. The mean dose-length product was 544.7 mGycm² compared to the reported radiation exposure of 1971–7946 mGycm² of CT-guided radio ablations. The one intra-operative complication was a superficial burn in the subcutaneous lesion in a tibia that was treated locally with no major influence on recovery.

Conclusions

RFA ablation guided by 3D O-arm stealth navigation is as effective as the traditional CT-guided technique with the advantage of lower radiation exposure.

Trial registration

Retrospective study number 0388–17-TLV at Tel Aviv Sourasky Medical Center IRB, approved at 25.10.17.

DICOM Metadata Analysis for Population Studies

This article reports an experimental study to determine how to use the stored Digital Imaging and Communication in Medicine (DICOM) metadata to perform population studies. As a case study, it was considered three types of medical imaging studies (i.e. routine head computed tomography, thorax computed radiography and thorax digital radiography) stored in the picture archiving and communication systems (PACS) of three healthcare institutions. The final sample consisted of DICOM metadata belonging to 1370360 images, corresponding to 109160 medical imaging studies performed on 72716 patients. The study followed a methodological approach that allows the identification of the number of patients with performed studies by age group and gender, as well as the average number of studies by patient, age group and gender in each one of the three healthcare institutions. The results show the relevance of the aggregation and analyses of DICOM metadata stored in heterogeneous PACS facilities.

Electronic collimation of radiographic images: does it comprise an overexposure risk?

OBJECTIVE

To investigate whether electronic collimation software, which is available in all digital X-ray systems, may comprise an overexposure risk.

METHODS

In the context of surveys on Diagnostic Reference Levels carried out in two radiographic facilities, along with data on exposure factors, the radiographic field sizes were also recorded. In one facility (Unit A), a wireless flat panel detector is used with a conventional X-ray unit, while in the other, a fully digital system is installed (Unit B). The electronically collimated image sizes were compared with the original radiation field sizes. The differences between these two systems concerning the field sizes and the mode of electronic collimation utilization were investigated.

RESULTS

In Unit A, manual electronic collimation was extensively used and cases where the radiation field size was up to three times larger than that electronically collimated, were identified. On the contrary, in Unit B radiation fields were smaller and electronic collimation was automatic.

CONCLUSION

When electronic collimation is used in manual mode instead of proper pre-exposure collimation, then it does comprise an overexposure risk. The risk is larger in radiographic units where the field size is not automatically selected according to the examination protocol and no interlocks against oversized collimation settings exist. Advances in knowledge: When radiologists review masked images to make the diagnosis, possible suboptimal X-ray field collimation practices may go unnoticed for long. Therefore, radiologists and medical physicists should periodically survey the original images to determine the actual radiation field sizes used for each radiographic examination type.

Estimation and comparison of the radiation effective dose during coronary computed tomography angiography examinations on single-source 64-MDCT and dual-source 128-MDCT

GOAL

To estimate and compare the radiation dose associated with coronary computed tomography angiography (CCTA) examinations on two multi-detector CT scanners (MDCT), 64-MDCT and 128-MDCT, in daily practice.

METHODS

Scan parameters of 90 patients undergoing retrospective electrocardiographic gating spiral CCTA exam were recorded during a period on a single-source 64-MDCT and a dual-source 128-MDCT, and average scan parameters were derived that were used for dosimetry. The computed tomography dose index (CTDI) with a pencil ionisation chamber and polymethyl methacrylate body phantom with diameter of 32 cm was measured on both scanners. The dose-length product (DLP) was calculated and the DLP to effective dose conversion factor (for chest scan at 120 kV of 0.014 mSv mGy^-1 cm^-1) was used to estimate effective dose (ED).

RESULTS

Patients' heart rate, scan length, pitch factor, CTDIv, DLP and ED for 128-MDCT were 64 (5) (beats min^-1), 161 (10) (mm), 0.26, 47 (12) (mGy), 769 (212) (mGy cm) and 10.3 (3.1) (mSv), respectively [mean (one standard deviation)]. Patients' heart rate, scan length, pitch factor, CTDIv, DLP and ED for 64-MDCT were 60 (7) (beats min^-1), 172 (14) (mm), 0.2, 60 (6) (mGy), 1068 (98) (mGy cm) and 14.9 (1.4) (mSv), respectively.

CONCLUSION

Our results indicated that the CTDIv, DLP and the effective dose with 128-MDCT is significantly lower than with 64-MDCT (p < 0.05). As differences between the exposure parameter mAs on two CT scanners was not significant (p > 0.05) and the kV was constant for both scanners (120 kV), the differences resulted from a shorter scan length on the 128-MDCT and use of a higher pitch factor (0.26 and 0.2 in the 128-MDCT and 64-MDCT, respectively). Comparison with other published studies confirms the findings and indicates methods for reducing patient dose.

A routine quality assurance test for CT automatic exposure control systems

The study purpose was to develop and validate a quality assurance test for CT automatic exposure control (AEC) systems based on a set of nested polymethylmethacrylate CTDI phantoms. The test phantom was created by offsetting the 16 cm head phantom within the 32 cm body annulus, thus creating a three part phantom. This was scanned at all acceptance, routine, and some nonroutine quality assurance visits over a period of 45 months, resulting in 115 separate AEC tests on scanners from four manufacturers. For each scan the longitudinal mA modulation pattern was generated and measurements of image noise were made in two annular regions of interest. The scanner displayed CTDIvol and DLP were also recorded. The impact of a range of AEC configurations on dose and image quality were assessed at acceptance testing. For systems that were tested more than once, the percentage of CTDIvol values exceeding 5%, 10%, and 15% deviation from baseline was 23.4%, 12.6%, and 8.1% respectively. Similarly, for the image noise data, deviations greater than 2%, 5%, and 10% from baseline were 26.5%, 5.9%, and 2%, respectively. The majority of CTDIvol and noise deviations greater than 15% and 5%, respectively, could be explained by incorrect phantom setup or protocol selection. Barring these results, CTDIvol deviations of greater than 15% from baseline were found in 0.9% of tests and noise deviations greater than 5% from baseline were found in 1% of tests. The phantom was shown to be sensitive to changes in AEC setup, including the use of 3D, longitudinal or rotational tube current modulation. This test methodology allows for continuing performance assessment of CT AEC systems, and we recommend that this test should become part of routine CT quality assurance programs. Tolerances of ±15% for CTDIvol and ±5% for image noise relative to baseline values should be used.

PACS number(s): 87.57.Q‐

Open-Source Radiation Exposure Extraction Engine (RE3) with Patient-Specific Outlier Detection

We present an open-source, picture archiving and communication system (PACS)-integrated radiation exposure extraction engine (RE3) that provides study-, series-, and slice-specific data for automated monitoring of computed tomography (CT) radiation exposure. RE3 was built using open-source components and seamlessly integrates with the PACS. RE3 calculations of dose length product (DLP) from the Digital imaging and communications in medicine (DICOM) headers showed high agreement (R (2) = 0.99) with the vendor dose pages. For study-specific outlier detection, RE3 constructs robust, automatically updating multivariable regression models to predict DLP in the context of patient gender and age, scan length, water-equivalent diameter (D w), and scanned body volume (SBV). As proof of concept, the model was trained on 811 CT chest, abdomen + pelvis (CAP) exams and 29 outliers were detected. The continuous variables used in the outlier detection model were scan length (R (2)  = 0.45), D w (R (2) = 0.70), SBV (R (2) = 0.80), and age (R (2) = 0.01). The categorical variables were gender (male average 1182.7 ± 26.3 and female 1047.1 ± 26.9 mGy cm) and pediatric status (pediatric average 710.7 ± 73.6 mGy cm and adult 1134.5 ± 19.3 mGy cm).

Measuring skin dose in CT examinations under complex geometries: Instruments, methods and considerations

OBJECTIVE

To investigate skin dose in Computed Tomography (CT) and its dependence on scanning geometry.

MATERIALS AND METHODS

Measurements of entrance surface air kerma (ESAK) in free air and entrance skin dose (ESD) on an anthropomorphic phantom were performed in a 64-slice CT scanner, using two different instruments: the Dose Profiler (DP) and the QED skin diode (QEDSD). Using DP and QEDSD, the ESAK rate profiles at the isocenter and at different distances from it, were measured using axial scans. Using DP and helical scans the ESAK rate profile in the Z-axis was acquired. The same profile was acquired with the QEDSD also, using many axial scans and manual table translation. ESD measurements were performed with the DP and QEDSD, in axial and helical scan mode.

RESULTS

ESAK measurements with DP and QEDSD were in good agreement, for both point dose and profile measurements. The agreement was also good for ESD measurements but not for helical scans, due to variable X-ray beam overlapping and different tube angular positions at each scan start. It was observed that the ESD values at different Y-axis offsets were comparable to the respective ESAK values recorded at the same Y-axis offset distances without the phantom.

CONCLUSIONS

Both DP and QEDSD were proven suitable for performing point ESD measurements. However, calculating the skin dose distribution in CT examinations is a very challenging task. A practical approach would be for CT scanners to provide a conservative estimate of the peak skin dose using the isocenter ESAK value.

Medical image file formats

Image file format is often a confusing aspect for someone wishing to process medical images. This article presents a demystifying overview of the major file formats currently used in medical imaging: Analyze, Neuroimaging Informatics Technology Initiative (Nifti), Minc, and Digital Imaging and Communications in Medicine (Dicom). Concepts common to all file formats, such as pixel depth, photometric interpretation, metadata, and pixel data, are first presented. Then, the characteristics and strengths of the various formats are discussed. The review concludes with some predictive considerations about the future trends in medical image file formats.

The Role of Virtual Cystoscopy, after Multidetector Computed Tomography Imaging Reconstruction without the Use of Contrast Medium, in the Diagnosis and Evaluations of Bladder Tumors: Preliminary Study

Introduction. Although conventional cystoscopy is considered to be the gold standard for diagnosis and follow-up of bladder tumors, it remains an invasive and costly procedure. With the advent of the multidetector CT (MDCT) scanners supported by specialized software virtual cystoscopy (VC) is possible. We assess the role of VC in diagnosing and evaluating bladder lesions. Materials and Methods. Between September 2010 and October 2011, 25 consecutive patients with cystoscopically confirmed bladder tumor underwent VC. The radiologists involved in this prospective study were blinded to the exact findings. After draining any residual urine with a catheter, the bladder was retrogradely insufflated with 200–600 cc of air. No intravenous or intravesical contrast was used. MDCT scan was performed in supine and prone positions and three-dimensional reconstruction of the urinary bladder was performed. Results. The examination was well tolerated by all patients with no complications. In total, 43 lesions were detected both with conventional cystoscopy and VC. Tumor size measured by CT ranged from 3 to 80 mm in diameter. The pathological report revealed noninvasive transitional cell carcinomas in all cases. Conclusion. VC has promising results in detecting exophytic bladder lesions. In the future it could be part of the diagnostic algorithm for bladder tumors.

Radiation dose in the thyroid and the thyroid cancer risk attributable to CT scans for pediatric patients in one general hospital of China

Objective: To quantify the radiation dose in the thyroid attributable to different CT scans and to estimate the thyroid cancer risk in pediatric patients. Methods: The information about pediatric patients who underwent CT scans was abstracted from the radiology information system in one general hospital between 1 January 2012 and 31 December 2012. The radiation doses were calculated using the ImPACT Patient Dosimetry Calculator and the lifetime attributable risk (LAR) of thyroid cancer incidence was estimated based on the National Academies Biologic Effects of Ionizing Radiation VII model. Results: The subjects comprised 922 children, 68% were males, and received 971 CT scans. The range of typical radiation dose to the thyroid was estimated to be 0.61–0.92 mGy for paranasal sinus CT scans, 1.10–2.45 mGy for head CT scans, and 2.63–5.76 mGy for chest CT scans. The LAR of thyroid cancer were as follows: for head CT, 1.1 per 100,000 for boys and 8.7 per 100,000 for girls; for paranasal sinus CT scans, 0.4 per 100,000 for boys and 2.7 per 100,000 for girls; for chest CT scans, 2.1 per 100,000 for boys and 14.1 per 100,000 for girls. The risk of thyroid cancer was substantially higher for girls than for the boys, and from chest CT scans was higher than that from head or paransal sinus CT scans. Conclusions: Chest CT scans caused higher thyroid dose and the LAR of thyroid cancer incidence, compared with paransal sinus or head CT scans. Therefore, physicians should pay more attention to protect the thyroid when children underwent CT scans, especially chest CT scans.

A comparison of methods to estimate organ doses in CT when utilizing approximations to the tube current modulation function

PURPOSE

Most methods to estimate patient dose from computed tomography (CT) exams have been developed based on fixed tube current scans. However, in current clinical practice, many CT exams are performed using tube current modulation (TCM). Detailed information about the TCM function is difficult to obtain and therefore not easily integrated into patient dose estimate methods. The purpose of this study was to investigate the accuracy of organ dose estimates obtained using methods that approximate the TCM function using more readily available data compared to estimates obtained using the detailed description of the TCM function.

METHODS

Twenty adult female models generated from actual patient thoracic CT exams and 20 pediatric female models generated from whole body PET∕CT exams were obtained with IRB (Institutional Review Board) approval. Detailed TCM function for each patient was obtained from projection data. Monte Carlo based models of each scanner and patient model were developed that incorporated the detailed TCM function for each patient model. Lungs and glandular breast tissue were identified in each patient model so that organ doses could be estimated from simulations. Three sets of simulations were performed: one using the original detailed TCM function (x, y, and z modulations), one using an approximation to the TCM function (only the z-axis or longitudinal modulation extracted from the image data), and the third was a fixed tube current simulation using a single tube current value which was equal to the average tube current over the entire exam. Differences from the reference (detailed TCM) method were calculated based on organ dose estimates. Pearson's correlation coefficients were calculated between methods after testing for normality. Equivalence test was performed to compare the equivalence limit between each method (longitudinal approximated TCM and fixed tube current method) and the detailed TCM method. Minimum equivalence limit was reported for each organ.

RESULTS

Doses estimated using the longitudinal approximated TCM resulted in small differences from doses obtained using the detailed TCM function. The calculated root-mean-square errors (RMSE) for adult female chest simulations were 9% and 3% for breasts and lungs, respectively; for pediatric female chest and whole body simulations RMSE were 9% and 7% for breasts and 3% and 1% for lungs, respectively. Pearson's correlation coefficients were consistently high for the longitudinal approximated TCM method, ranging from 0.947 to 0.999, compared to the fixed tube current value ranging from 0.8099 to 0.9916. In addition, an equivalence test illustrated that across all models the longitudinal approximated TCM is equivalent to the detailed TCM function within up to 3% for lungs and breasts.

CONCLUSIONS

While the best estimate of organ dose requires the detailed description of the TCM function for each patient, extracting these values can be difficult. The presented results show that an approximation using available data extracted from the DICOM header provides organ dose estimates with RMSE of less than 10%. On the other hand, the use of the overall average tube current as a single tube current value was shown to result in poor and inconsistent estimates of organ doses.

A comprehensive method for calculating patient effective dose and other dosimetric quantities from CT DICOM images

OBJECTIVE

The purpose of this article is to present a method for the calculation of effective dose using the DICOM header information of CT images.

MATERIALS AND METHODS

Using specialized software, the DICOM data were automatically extracted into a spreadsheet containing embedded functions for calculating effective dose. These data were used to calculate the dose-length product (DLP) fraction that corresponds to each image, and the respective effective dose was obtained by multiplying the image DLP by a conversion coefficient that was automatically selected depending on the CT scanner, the tube potential, and the anatomic position to which each image corresponded. The total effective dose was calculated as the sum of effective doses of all images plus the contribution of overscan. The conversion coefficient tables were derived using dosimetry calculator software for both the International Commission on Radiological Protection (ICRP) 60 and ICRP 103 organ-weighting schemes. This method was applied for 90 chest, abdomen-pelvis, and chest-abdomen-pelvis examinations performed in three different MDCT scanners.

RESULTS

The DLP values calculated with this method were in good agreement with those calculated by the CT scanners' software. The effective dose values calculated using the ICRP 103 conversion coefficient compared with those calculated using the ICRP 60 conversion coefficient were roughly equal for the chest-abdomen-pelvis examinations, smaller for the abdomen-pelvis examinations, and larger for the chest examinations. The applicability of this method for estimating organ doses was also explored.

CONCLUSION

With this method, all patient dose-related quantities, such as the DLP, effective dose, and individual organ doses, can be calculated.