Contrast thresholds for detection of various iodine concentrations in subtraction CT and dual-energy CT systems.

OBJECTIVE: To estimate the minimum iodine concentrations detectable in simulated vessels of various diameters for both subtraction computed tomography (CT) and dual-energy CT systems. METHODS: Fillable tubes (diameters: 1, 3, and 5 mm) were filled with a variety of iodine concentrations (range: 0-20 mg/ml), placed in the center of 28-mm cylindrical rods and surrounded with water. Rods with and without fillable tubes were placed in a 20-cm cylindrical solid-water phantom to simulate administration of iodine in blood vessels. The phantom was scanned with clinical subtraction CT (SCT) and dual-energy CT (DECT) head protocols to assess the detection of minimum iodine concentrations in both systems. The SCT and DECT images were evaluated quantitatively with a MATLAB script to extract regions of interest (ROIs) of each simulated vessel. ROI measurements were used to calculate the limit of detectability (LOD) and signal-to-noise ratio of Rose criteria for the assessment of the contrast thresholds. RESULTS: Both SNRRose and LOD methods agreed and determined the minimum detectable iodine concentration to be 0.4 mg/ml in the 5-mm diameter vessel for SCT. However, the minimum detectable concentration in the 5-mm vessel with DECT was 1 mg/ml. The 3-mm vessel had a minimum detectable concentration of 0.8 mg/ml for SCT and 2 mg/ml for DECT. Lastly, the minimum detectable iodine concentration for the 1-mm vessel was 10 mg/ml for SCT and 10 mg/ml for DECT. CONCLUSION: In this phantom study, SCT showed the capability to detect lower iodine concentrations compared to DECT. Contrast thresholds varied for vessels of different diameters and the smaller vessels required a higher iodine concentration for detection. Based on this knowledge, radiologists can modify their protocols to increase contrast enhancement.

Comparison of metal artifact reduction using single-energy CT and dual-energy CT with various metallic implants in cadavers.

OBJECTIVES: The purpose of this study was to compare the effectiveness of metal artifact reduction using Single Energy Metal Artifact Reduction (SEMAR) and Dual Energy CT (DECT). MATERIALS AND METHODS: Six cadavers containing metal implants in the head, neck, abdomen, pelvis, and extremities were scanned with Standard, SEMAR, and DECT protocols on a 320-slice CT scanner. Four specialized radiologists blinded to acquisition methods rated severity of metal artifacts, visualization of anatomic structures, diagnostic interpretation, and image preference with a 5-point grading scale. RESULTS: Scores were significantly better for SEMAR than Standard images in the hip, knee, pelvis, abdomen, and maxillofacial scans (3.25 ±â€¯0.88 versus 2.14 ±â€¯0.93, p < 0.001). However, new reconstruction artifacts developed in SEMAR images that were not present in Standard images. Scores for severity of metal artifacts and visualization of smooth structures were significantly better for DECT than Standard images in the cervical spine (3.50±0.50 versus 2.0±0.58, p < 0.001) and was preferred over Standard images by one radiologist. In all other cases, radiologists preferred the Standard image over the DECT image due to increased image noise and reduced low-contrast resolution with DECT. In all cases, SEMAR was preferred over Standard and DECT images. CONCLUSION: SEMAR was more effective at reducing metal artifacts than DECT. Radiologists should be aware of new artifacts and review both the original and SEMAR images. When the anatomy or implant is relatively small, DECT may be superior to SEMAR without additional artifacts. However, radiologist should be aware of a reduction in soft tissue contrast.

Impact of patient centering in CT on organ dose and the effect of using a positioning compensation system: Evidence from OSLD measurements in postmortem subjects.

The purpose of this study was to investigate the frequency and impact of vertical mis-centering on organ doses in computed tomography (CT) exams and evaluate the effect of a commercially available positioning compensation system (PCS). Mis-centering frequency and magnitude was retrospectively measured in 300 patients examined with chest-abdomen-pelvis CT. Organ doses were measured in three postmortem subjects scanned on a CT scanner at nine different vertical table positions (maximum shift ± 4 cm). Organ doses were measured with optically stimulated luminescent dosimeters inserted within organs. Regression analysis was performed to determine the correlation between organ doses and mis-centering. Methods were repeated using a PCS that automatically detects the table offset to adjust tube current output accordingly. Clinical mis-centering was >1 cm in 53% and 21% of patients in the vertical and lateral directions, respectively. The 1-cm table shifts resulted in organ dose differences up to 8%, while 4-cm shifts resulted in organ dose differences up to 35%. Organ doses increased linearly with superior table shifts for the lung, colon, uterus, ovaries, and skin (R2  = 0.73-0.99, P < 0.005). When the PCS was utilized, organ doses decreased with superior table shifts and dose differences were lower (average 5%, maximum 18%) than scans performed without PCS (average 9%, maximum 35%) at all table shifts. Mis-centering occurs frequently in the clinic and has a significant effect on patient dose. While accurate patient positioning remains important for maintaining optimal imaging conditions, a PCS has been shown to reduce the effects of patient mis-centering.

Current state of practice regarding digital radiography exposure indicators and deviation indices: Report of AAPM Imaging Physics Committee Task Group 232.

Beginning with the advent of digital radiography systems in 1981, manufacturers of these systems provided indicators of detector exposure. These indicators were manufacturer-specific, and users in facilities with equipment from multiple manufacturers found it a challenge to monitor and manage variations in indicated exposure in routine clinical use. In 2008, a common definition of exposure index (EI) was realized in International Electrotechnical Commission (IEC) International Standard 62494-1 Ed. 1, which also introduced and defined the deviation index (DI), a number quantifying the difference between the detector EI for a given radiograph and the target exposure index (EIT ). An exposure index that differed by a constant from that established by the IEC and the concept of the deviation index also appear in American Association of Physicists in Medicine (AAPM) Report No. 116 published in 2009. The AAPM Report No. 116 went beyond the IEC standard in supplying a table (Table II in the report of TG-116) titled "Exposure Indicator DI Control Limits for Clinical Images," which listed suggested DI ranges and actions to be considered for each range. As the IEC EI was implemented and clinical DI data were gathered, concerns were voiced that the DI control limits published in the report of TG-116 were too strict and did not accurately reflect clinical practice. The charge of task group 232 (TG-232) and the objective of this final report was to investigate the current state of the practice for CR/DR Exposure and Deviation Indices based on AAPM TG 116 and IEC-62494, for the purpose of establishing achievable goals (reference levels) and action levels in digital radiography. Data corresponding to EI and DI were collected from a range of practice settings for a number of body parts and views (adults and pediatric radiographs) and analyzed in aggregate and separately. A subset of radiographs was also evaluated by radiologists based on criteria adapted from the European Guidelines on Quality Criteria for Diagnostic Radiographic Images from the European Commission. Analysis revealed that typical DI distribution was characterized by a standard deviation (SD) of 1.3-3.6 with mean DI values substantially different from 0.0, and less than 50% of DI values fell within the significant action limits proposed by AAPM TG-116 (-1.0 ≤ DI ≤ 1.0). Recommendations stemming from this analysis include targeting a mean DI value of 0.0 and action limits at ±1 and ±2 SD of the DI based on actual DI data of an individual site. EIT values, DI values, and associated action limits should be reviewed on an ongoing basis and optimization of DI values should be a process of continuous quality improvement with a goal of reducing practice variation.

Determining Organ Doses from CT with Direct Measurements in Postmortem Subjects: Part 2--Correlations with Patient-specific Parameters.

PURPOSE: To generate empirical sets of equations that can be used to calculate patient-specific organ doses resulting from a group of computed tomographic (CT) studies by using data from direct dose measurements performed within a human body. MATERIALS AND METHODS: Organ dose measurements were obtained in eight postmortem female subjects. A chest-abdomen-pelvis protocol was used for this study. The relationships among measured organ doses, body mass index, effective diameter (D(eff)), and volume CT dose index (CTDI(vol)) were investigated. Organ dose equations were developed by means of linear regression from organ dose data, with CTDI(vol) and D(eff) as variables, by using Pearson correlation coefficients and P values to determine correlation strength of fit. Measured organ doses were compared with corresponding size-specific dose estimates (SSDEs). RESULTS: The central-section D(eff) presented similar correlations with organ doses to those from D(eff) measured at specific organ locations. The strongest correlations were observed between the central-section D(eff) and CTDI(vol)-normalized organ doses (R(2): 0.478-0.941). The average of measured organ doses for each subject resulted in an average difference of only 5% from SSDE-calculated doses; however, individual organ doses differed from +31% to -61% from the calculated SSDE. CONCLUSION: The organ dose equations developed represent a method for organ dose estimation from direct organ dose measurements that can estimate organ doses more accurately than the calculated SSDE, which provides a less-specific patient dose estimate.

Determining Organ Doses from CT with Direct Measurements in Postmortem Subjects: Part 1--Methodology and Validation.

PURPOSE: To develop a methodology that allows direct measurement of organ doses from computed tomographic (CT) examinations of postmortem subjects. MATERIALS AND METHODS: In this institutional review board approved study, the x-ray linear attenuation coefficients of various tissues were calculated from the mean CT numbers of images that were obtained in eight embalmed adult female cadavers and compared with the corresponding linear attenuation coefficients calculated from CT images obtained in eight living patients that were body mass index (BMI)-matched. Dosimetry was performed in three of the cadavers by accessing organs of interest and affixing partially sealed vinyl tubes inside them. Optically stimulated luminescent dosimeters (OSLDs) were inserted into the tubes and positioned within the organs of interest and on the skin. OSLDs were read with an InLight MicroStar (Landauer, Glenwood, Ill) reader, and readings were corrected for energy and scatter response. Fifteen tubes containing dosimeters were used, and imaging was repeated twice in each cadaver, for a total of five standard clinical protocols. Average dosimetry values were used for analysis. RESULTS: Differences in linear attenuation coefficients between living and embalmed cadaveric tissues were within 3% for the tissues investigated. Measured organ doses for a chest-abdomen-pelvis CT protocol were less than 32 mGy for all organs measured. Organs that were completely irradiated during a given examination received similar doses, whereas organs that were partially irradiated displayed a large variation in measured organ dose. CONCLUSION: The anatomic and radiation attenuation characteristics of cadavers are comparable to those of living human tissue. This methodology allows direct measurement of organ doses from clinical CT examinations.

Workflow efficiency comparison of a new CR system with traditional CR and DR systems in an orthopedic setting.

Workflow efficiency is a crucial factor in selecting computed radiography (CR) versus digital radiography (DR) systems for digital projection radiography operations. DR systems can be more efficient, but present higher costs and limitations in performing some radiographic exams. A newly developed CR system presents a good alternative with its faster line-by-line instead of pixel-by-pixel image plate-scanning technology and a more efficient workstation. To evaluate workflow characteristics, a time-motion study was conducted to compare radiographic exam times of the new CR system with traditional CR and DR systems in a high-volume orthopedic operation. Approximately 200 exams for each modality were documented from the moment when a patient entered the X-ray room to the moment when all images were sent to the PACS archive using a timer and speech-recognition software. Applying Welch ANOVA and Tamhane's T2 tests, average exam times for the new CR system were significantly faster (18-42%; P ≤ 0.025) than for the traditional CR system. Average exam times for the DR system were also faster than for the new CR system by 22-36% (P<0.001) with one exception. In the case where the new CR system was located outside the X-ray room, using a one-technologist workflow model, average single-study exam times were not significantly different from those found when using DR. Therefore, the new CR system may be comparable in efficiency with the DR system for this particular setting and operation.

Radiation exposure with use of the mini-C-arm for routine orthopaedic imaging procedures.

BACKGROUND: The use of mobile fluoroscopic devices during orthopaedic procedures is associated with substantial concern with regard to the radiation exposure to surgeons and support staff. The perceived increased risks associated with large c-arm devices have been well documented. However, no study to date has documented the relative radiation risk associated with the use of a mini-c-arm device. The purpose of the current study was to determine the amount of radiation received by the surgeon during the use of a mini-c-arm device and to compare this amount with documented measurements associated with the large c-arm device. METHODS: With use of a radiation dosimeter, measurements were carried out with tissue-equivalent anthropomorphic phantoms to quantitatively determine exposure rates at various locations and distances from the mini-c-arm for two common upper and lower extremity procedures. RESULTS: Regardless of position, distance, or relative duration of exposure, exposure rates resulting from the use of the mini-c-arm device were one to two orders of magnitude lower than those reported in the literature in association with the use of the large c-arm device. CONCLUSIONS: The mini-c-arm device should be utilized whenever feasible in order to eliminate many of the concerns associated with use of the large c-arm device, specifically those related to cumulative radiation hazards, positioning considerations, relative distance from the beam, and the need for protective shielding.

Evaluating radiographic parameters for mobile chest computed radiography: phantoms, image quality and effective dose.

Conventional chest radiography is technically difficult because of wide variations in tissue attenuations in the chest and limitations of screen-film systems. Mobile chest radiography, performed bedside on hospital inpatients, presents additional difficulties due to geometric and equipment limitations inherent in mobile x-ray procedures and the severity of illness in the patients. Computed radiography (CR) offers a different approach for mobile chest radiography by utilizing a photostimulable phosphor. Photostimulable phosphors overcome some image quality limitations of mobile chest imaging, particularly because of the inherent latitude. Because they are more efficient in absorbing lower-energy x-rays than rare-earth intensifying screens, this study evaluated changes in kVp for improving mobile chest CR. Three commercially available systems were tested, with the goal of implementing the findings clinically. Exposure conditions (kVp and grid use) were assessed with two acrylic-and-aluminum chest phantoms which simulated x-ray attenuation for average-sized and large-sized adult chests. These phantoms contained regions representing the lungs, heart and subdiaphragm to allow proper CR processing. Signal-to-noise ratio (SNR) measurements using different techniques were obtained for acrylic and aluminum disks (1.9 cm diameter) superimposed in the lung and heart regions of the phantoms, where the disk thicknesses (contrast) were determined from disk visibility. Effective doses to the phantoms were also measured for these techniques. The results indicated that using an 8:1, 33 lines/cm antiscatter grid improved the SNR by 60-300 % compared with nongrid images, depending on phantom and region; however, the dose to the phantom also increased by 400-600%. Lowering x-ray tube potential from 80 to 60 kVp improved the SNR by 30-40%, with a corresponding increase in phantom dose of 40-50%. Increasing the potential from 80 to 100 kVp reduced both the SNR and the phantom dose by approximately 10%. The most promising changes in technique for trial in clinical implementation include using an antiscatter grid, especially for large patients, and potentially increasing kVp.

Enterprise-wide CR implementation: the Shands Healthcare System experience.

Major healthcare systems are comprised of hospitals and clinics of different sizes and locations. Many such enterprises are already using picture archiving and communication systems (PACS) and computed radiography (CR) in their main hospitals. The integration of other hospitals and clinics into PACS is a more complex problem. The introduction of CR in remote facilities presents problems, as patient populations, department sizes, and work flow patterns may differ among facilities, and inadequate implementation programs may lead to disruption of patient care services. Although the University of Florida has had an operating PACS for years, facilities affiliated with the Shands Healthcare System (SHS) had not been incorporated into PACS until recently. This article presents the 5-year process to convert all film-screen radiological services to CR in the main hospital, five affiliated community hospitals, and four clinics. The article shows the importance of leadership by the medical physicist from inception of the project through installation and clinical implementation.