Investigation of Scattered Radiation Reduction Effect by Use of Collimator Cover Covered with Leaded Sheet in Angiography Equipment.

The purpose of this study was to investigate the effect of scattered radiation reduction to medical staff by attaching the leaded sheet on the collimator cover of the angiography equipment. Ambient dose equivalent was measured to compare the rate of scattered radiation reduction between with and without the leaded sheet. Shielding effect was confirmed for scattered radiation in all directions, especially 27% of shielding ratio in the head and neck area when angiography equipment installed with small detector, and more than 40% of shielding ratio when adjusting a cut portion of leaded sheet to the field size. However, it decreased when the dose area product meter was not attached. Therefore, our proposed leaded sheet can reduce radiation dose to medical staff during angiographic and interventional procedures.

Software Development for Estimating the Conversion Factor (K-Factor) at Suitable Scan Areas, Relating the Dose Length Product to the Effective Dose.

We developed a k-factor-creator software (kFC) that provides the k-factor for CT examination in an arbitrary scan area. It provides the k-factor from the effective dose and dose-length product by Imaging Performance Assessment of CT scanners and CT-EXPO. To assess the reliability, we compared the kFC-evaluated k-factors with those of the International Commission on Radiological Protection (ICRP) publication 102. To confirm the utility, the effective dose determined by coronary computed tomographic angiography (CCTA) was evaluated by a phantom study and k-factor studies. In the CCTA, the effective doses were 5.28 mSv in the phantom study, 2.57 mSv (51%) in the k-factor of ICRP, and 5.26 mSv (1%) in the k-factor of the kFC. Effective doses can be determined from the kFC-evaluated k-factors in suitable scan areas. Therefore, we speculate that the flexible k-factor is useful in clinical practice, because CT examinations are performed in various scan regions.

Electrocardiogram-gated coronary CT angiography dose estimates using ImPACT.

The primary study objective was to assess radiation doses using a modified form of the Imaging Performance Assessment of Computed Tomography (CT) scanner (ImPACT) patient dosimetry for cardiac applications on an Aquilion ONE ViSION Edition scanner, including the Ca score, target computed tomography angiography (CTA), prospective CTA, continuous CTA/cardiac function analysis (CFA), and CTA/CFA modulation. Accordingly, we clarified the CT dose index (CTDI) to determine the relationship between heart rate (HR) and X-ray exposure. As a secondary objective, we compared radiation doses using modified ImPACT, a whole-body dosimetry phantom study, and the k-factor method to verify the validity of the dose results obtained with modified ImPACT. The effective dose determined for the reference person (4.66 mSv at 60 beats per minute (bpm) and 33.43 mSv at 90bpm) were approximately 10% less than those determined for the phantom study (5.28 mSv and 36.68 mSv). The effective doses according to the k-factor (0.014 mSv•mGy-1•cm-1; 2.57 mSv and 17.10 mSv) were significantly lower than those obtained with the other two methods. In the present study, we have shown that ImPACT, when modified for cardiac applications, can assess both absorbed and effective doses. The results of our dose comparison indicate that modified ImPACT dose assessment is a promising and practical method for evaluating coronary CTA.

Tube Current Modulation Between Single- and Dual-Energy CT With a Second-Generation Dual-Source Scanner: Radiation Dose and Image Quality.

OBJECTIVE: The purpose of this study was to compare the effects of tube current modulation between single- and dual-energy CT with a second-generation dual-source scanner. MATERIALS AND METHODS: Custom-made elliptic polymethylmethacrylate phantoms for slim and large patients were used. Absorbed radiation dose at the central point of the phantoms was measured with a solid-state detector while the phantoms were scanned in single-energy (120 kV) and dual-energy (100/Sn140, 80/Sn140, and 140/80 kV) modes with a second-generation dual-source CT scanner. Tube current modulation was activated in both modes, and quality reference tube current-time settings of 150, 300, 450, and 600 mAs were selected. Scanning was performed three times under the same conditions, and image noise was evaluated by measuring the SD of CT numbers in four separate regions of three adjacent images of the phantoms. RESULTS: Absorbed dose increased and image noise decreased with an increase in quality reference tube current-time setting when the slim phantom was scanned. For the large phantom, the radiation dose and noise level reached a plateau above quality reference tube current-time settings of 300 mAs for 100/Sn140 kV and 450 mAs for 120 kV. The radiation dose was small and the noise level was large with 80/Sn140 kV compared with that obtained with 120 and 100/Sn140 kV at all quality reference tube current-time settings. CONCLUSION: When a large phantom is scanned with 100/Sn140 kV, exposure demand for tube current modulation exceeds system limits at a lower quality reference tube current-time setting than for scanning 120 kV.

128-slice dual-source CT coronary angiography with prospectively electrocardiography-triggered high-pitch spiral mode: radiation dose, image quality, and diagnostic acceptability.

BACKGROUND: Dual-source computed tomography (CT) enables CT coronary angiography (CTCA) with a prospectively electrocardiography (ECG)-triggered high-pitch spiral (HPS) mode. PURPOSE: To evaluate the radiation dose, image quality, and diagnostic acceptability of the HPS mode in CTCA and to compare HPS with the step-and-shoot (SAS) and low-pitch spiral (LPS) modes. MATERIAL AND METHODS: One hundred and thirty-eight patients who underwent CTCA with a 128-slice dual-source CT scanner were retrospectively included in this study. Seventeen patients (average heart rate of ≤65 beats per minute [bpm] prior to acquisition) were evaluated in the HPS mode, 88 (average heart rate of >65 and ≤80 bpm prior to acquisition) in the SAS mode, and 33 (average heart rate of >80 bpm prior to acquisition or patients with an unstable heart rhythm) in the LPS mode. Radiation dose and image noise were recorded for each patient. Diagnostic acceptability was graded using a four-point scale (1, unacceptable; 2, suboptimal; 3, acceptable; 4, fully acceptable). RESULTS: The effective dose in the HPS mode was 1.5 ± 0.2 mSv, which was lower than that in SAS (8.9 ± 2.7 mSv) and LPS (21.5 ± 4.3 mSv) modes. There were no significant differences in the image noise levels in the descending aorta and left atrium. The average per-patient diagnostic acceptability was 3.2, 3.6, and 3.7 in HPS, SAS, and LPS modes, respectively. CONCLUSION: The radiation dose is lower with HPS than with other modes, and the HPS mode-acquired images of patients with heart rates of ≤65 bpm are nearly acceptable for diagnostic image interpretation.

Nationwide survey of radiation exposure during pediatric computed tomography examinations and proposal of age-based diagnostic reference levels for Japan.

BACKGROUND: Diagnostic reference levels (DRLs) have not been established in Japan. OBJECTIVE: To propose DRLs for CT of the head, chest and abdomen for three pediatric age groups. MATERIALS AND METHODS: We sent a nationwide questionnaire by post to 339 facilities. Questions focused on pediatric CT technology, exposure parameters, CT protocols, and radiation doses for age groups <1 year, 1-5 years, and 6-10 years. RESULTS: For the three age groups in the 196 facilities that responded, the 75th percentile values of volume CT dose index based on a 16-cm phantom (CTDIvol 16 [mGy]) for head, chest and abdominal CT were for infants 39.1, 11.1 and 12.0, respectively; for 1-to 5-year-olds 46.9, 14.3 and 16.7, respectively; and for 6-to 10-year-olds 67.7, 15.0 and 17.0, respectively. The corresponding dose­length products (DLP 16 [mGy・cm]) for head, chest and abdominal CT were for infants 526.1, 209.1 and 261.5, respectively; for 1-to 5-year-olds 665.5, 296.0 and 430.8, respectively; and for 6-to 10-year-olds 847.9, 413.0 and 532.2, respectively. CONCLUSION: The majority of CTDIvol 16 and DLP 16 values for the head were higher than DRLs reported from other countries. For risk reduction, it is necessary to establish DRLs for pediatric CT in Japan.

[Properties and usage of radiophotoluminescent glass dosimeters for computed tomography dosimetry].

There are two types of radiophotoluminescent glass dosimeters (RPLDs). One has a tin filter in the capsule (GD-352M) and the other has no filter (GD-302M). The purpose of our study was to evaluate the properties of these RPLDs for computed tomography (CT) dosimetry: energy dependence, variation, angular dependence, and dose distribution in a single slice. Energy dependence and variation were investigated for ratio of the air kerma measured by RPLDs to that by ion chamber. Angular dependence was investigated for RPLDs and ion chamber. RPLDs were irradiated at 90°, 60°, 30°, 0°, -30°, -60°, and -90°: 0° was vertical to long axial direction of the RPLD, and plus and minus meant clockwise and anti-clockwise, respectively. Dose distribution in a single slice of an anthropomorphic phantom was acquired using 46 RPLDs. The dose responses of GD-302M and GD-352M depended on beam energy and irradiation angle of X-ray, respectively. The dose variation among dosimeters was large with GD-352M. The dose obtained from GD-352M was lower than that from GD-302M. It was expected that the dose distribution of GD-352M was formed by the primary X-ray, so RPLD without tin filter should be used for CT dosimetry.

The use of positron emission tomography/computed tomography imaging in radiation therapy: a phantom study for setting internal target volume of biological target volume.

BACKGROUND: Fluorodeoxyglucose ((18)F-FDG) positron emission tomography/computed tomography (PET/CT) is an important method for detecting tumours, planning radiotherapy treatment, and evaluating treatment responses. However, using the standardized uptake value (SUV) threshold with PET imaging may be suitable not to determine gross tumour volume but to determine biological target volume (BTV). The aim of this study was to extract internal target volume of BTV from PET images. METHODS: Three spherical densities of (18)F-FDG were employed in a phantom with an air or water background with repetitive motion amplitudes of 0-30 mm. The PET data were reconstructed with attenuation correction (AC) based on CT images obtained by slow CT scanning (SCS) or helical CT scanning (HCS). The errors in measured SUVmax and volumes calculated using SUV threshold values based on SUVmax (THmax) in experiments performed with varying extents of respiratory motion and AC were analysed. RESULTS: A partial volume effect (PVE) was not observed in spheres with diameters of ≥ 28 mm. When calculating SUVmax and THmax, using SCS for AC yielded smaller variance than using HCS (p<0.05). For spheres of 37- and 28-mm diameters in the phantom with either an air or water background, significant differences were observed when mean THmax of 30-, 20-, or 10-mm amplitude were compared with the stationary conditions (p<0.05). The average THmax values for 37-mm and 28-mm spheres with an air background were 0.362 and 0.352 in non-motion, respectively, and the mean THmax values for 37-mm and 28-mm spheres with a water background were 0.404 and 0.387 in non-motion and 0.244 and 0.263 in motion, respectively. When the phantom background was air, regardless of sphere concentration or size, THmax was dependent only on motion amplitude. CONCLUSIONS: We found that there was no PVE for spheres with ≥ 28-mm diameters, and differences between SUVmax and THmax were reduced by using SCS for AC. In the head-and-neck and the abdomen, the standard values of THmax were 0.25 and 0.40 with and without respiratory movement, respectively. In the lungs, the value of THmax became the approximate expression depending on motion amplitude.

Evaluation of the CT dose index for scans with an ECG using a 320-row multiple-detector CT scanner.

The relationship between heart rate (HR) and computed tomography dose index (CTDI) was evaluated using an electrocardiogram (ECG) gate scan for scan applications such as prospective triggering, Ca scoring, target computed tomography angiography (CTA), prospective CTA and retrospective gating, continuous CTA/CFA (cardiac functional analysis) and CTA/CFA modulation. Even in the case of a volume scan, doses for the multiple scan average dose were similar to those for CTDI. Moreover, it was found that the ECG gate scan yields significantly different doses. When selecting the optimum scan, the doses were dependent on many factors such as HR, scan rotation time, active time, prespecified cardiac phase and modulation rate. Therefore, it is necessary to take these results into consideration when selecting the scanning parameters.

Investigation of qualitative and quantitative factors related to radiological exposure to nursing staff during computed tomography examinations.

Radiologists or nurses intermittently stay in computed tomography rooms during computed tomography examinations; these actions are defined as "entrance actions." The qualitative and quantitative factors related to radiological exposure to computed tomography nursing staff were investigated to identify the protective measures against entrance actions. A questionnaire survey was used to investigate the frequency, motives, and causalities of entrance actions. Individual and area monitoring were simultaneously performed. The mean frequency of entrance actions was 1.2 times mo(−1). The primary motive for entrance actions was to dispel anxieties regarding collateral accidents during computed tomography. The nursing staff particularly engaged in close supervision to help the patients cope with contrast media extravasation. The average personal dose equivalent [Hp(10)] to the nurses was 0.21 mSv mo(−1). The ambient dose equivalent [H*(10)] rate was 1.4­3.7 mSv min(−1) at a distance of 1 m from CT gantry centre. Avoidance of entrance actions and collateral accidents would decrease the occupational exposures to nurses.

Evaluation of organ doses and effective dose according to the ICRP Publication 110 reference male/female phantom and the modified ImPACT CT patient dosimetry.

We modified the Imaging Performance Assessment of CT scanners (ImPACT) to evaluate the organ doses and the effective dose based on the International Commission on Radiological Protection (ICRP) Publication 110 reference male/female phantom with the Aquilion ONE ViSION Edition scanner. To select the new CT scanner, the measurement results of the CTDI100,c and CTDI100,p for the 160 (head) and the 320 (body) mm polymethylmethacrylate phantoms, respectively, were entered on the Excel worksheet. To compute the organ doses and effective dose of the ICRP reference male/female phantom, the conversion factors obtained by comparison between the organ doses of different types of phantom were applied. The organ doses and the effective dose were almost identical for the ICRP reference male/female and modified ImPACT. The results of this study showed that, with the dose assessment of the ImPACT, the difference in sex influences only testes and ovaries. Because the MIRD-5 phantom represents a partially hermaphrodite adult, the phantom has the dimensions of the male reference man including testes, ovaries, and uterus but no female breasts, whereas the ICRP male/female phantom includes whole-body male and female anatomies based on high-resolution anatomical datasets. The conversion factors can be used to estimate the doses of a male and a female accurately, and efficient dose assessment can be performed with the modified ImPACT.

[Radiation dose evaluation in a photon-counting digital mammography unit].

The purpose of our study was to evaluate radiation dose and beam quality in photon-counting digital mammography (PCDM) and compare them with those in a full-field digital mammography (FFDM) unit. Dose variation in the X-ray tube axis direction, aluminum half-value layer, average glandular and skin doses, and contrast-to-noise ratio (CNR) were evaluated for the PCDM and FFDM units. In PCDM, the dose variation in the X-ray tube axis direction was greater than that in FFDM. At a tube voltage of 28 kV, the first half-value layers were 0.407 mmAl for PCDM, 0.357 mmAl for FFDM with a molybdenum target and molybdenum filter (Mo/Mo), and 0.579 mmAl for FFDM with a tungsten target and rhodium filter (W/Rh). The average glandular doses with 45-mm-equivalent breast thickness were 0.723 mGy for the PCDM, 1.55 mGy for the FFDM with Mo/Mo in low-dose mode, and 0.835 mGy for the FFDM with W/Rh in low-dose mode. In PCDM, the skin dose was equivalent to or lower than that in FFDM. The CNR was 2.65±0.04, 2.35±0.04, and 2.52±0.03 for the PCDM, FFDM with Mo/Mo, and that with W/Rh, respectively. The CNR for PCDM was significantly higher than that for FFDM (p<0.001). It is therefore possible to reduce the radiation dose to the patient by using a PCDM unit while maintaining a significantly higher CNR than with the FFDM unit.

[A comparison of several convenient methods of estimating effective energy in X-ray computed tomography].

The measurement of half-value layers (HVLs) and effective energy in X-ray computed tomography (CT) using conventional nonrotating methods is regarded as a highly challenging task, as it necessitates the use of a nonrotating X-ray tube and the assistance of service engineers. Several convenient methods have been proposed to circumvent this limitation; however, to the best of our knowledge, there are no reports that provide a comparative study on the accuracy of each method. This prompted us to compare the accuracy and practicality of each method. Effective energy was calculated using four methods: lead shielding, copper pipe, localization, and inner-metal center-air ratio (IMCAR). The accuracy of each method for the measurement of effective energy in X-ray CT was evaluated and compared with the conventional nonrotating method. The differences in the effective energy were 0.0 to 0.6 keV (0.0% to 1.1%) for lead shielding, -2.2 to -0.6 keV (1.4% to 4.3%) for copper pipe, 4.7 to 16.7 keV (9.9% to 31.4%) for localization, and -7.4 to -0.3 keV (0.6% to 17.5%) for the IMCAR method. The results indicate that the lead shielding method is the most accurate and practical method of estimating effective energy in X-ray CT.

A novel removable shield attached to C-arm units against scattered X-rays from a patient's side.

OBJECTIVES: We invented a drape-like shield against scattered X-rays that can safely come into contact with medical equipment or people during fluoroscopically guided procedures. The shield can be easily removed from a C-arm unit using one hand. We evaluated the use of the novel removable shield during the endoscopic retrograde cholangiopancreatography (ERCP) procedure. METHODS: We measured the dose rate of scattered X-rays around endoscopists with and without this removable shield and surveyed the occupational doses to the ERCP staff. We also examined the endurance of the shield. RESULTS: The removable shield reduced the dose rate of scattered X-rays to one-tenth and reduced the monthly dose to an endoscopist by at least two-fifths. For 2.5 years, there was no damage to the shield and no loosening of the seam. The bonding of the hook-and-loop fasteners did not weaken, although the powerful double-sided tapes made especially for plastic did. CONCLUSIONS: The removable shield can reduce radiation exposure to the ERCP staff and may contribute to reducing the exposure to the eye lenses of operators. It would also be possible to expand its use to other fluoroscopically guided procedures besides ERCP because it is a light, simple, and useful device. KEY POINTS: • We invented a shield that can be removed from C-arm units with one hand. • The removable shield reduces the dose rate of X-rays to one-tenth. • The removable shield reduces operator exposure by two-fifths. • The removable shield is durable, lasting for several years. • The drape-like removable shield is light, simple, and useful.

Differences in behavior of tube current modulation techniques for thoracic CT examinations between male and female anthropomorphic phantoms.

Our objective was to investigate the differences in behavior of tube current modulation (TCM) techniques for thoracic CT examinations between male and female anthropomorphic phantoms. The phantoms were scanned with an automatic exposure control system in the longitudinal (z-) and angular-longitudinal (xyz-) TCM, in addition to the fixed-mA which was used as a reference. Axial dose distributions were measured at the levels of the breasts and the diaphragm, and longitudinal dose distributions were measured from the thoracic-inlet level to the diaphragm level at the center and periphery of the phantoms by use of eight solid-state detectors. Image noise was quantitatively measured continuously from the top to the bottom images of the phantoms. With the male phantom, the percentage of average absorbed dose with the xyz-TCM mode compared to the z-TCM mode was 90.2 % at the level of the nipples. This value was significantly smaller than that for the female phantom (95.6 %, P < 0.0001). With either phantom, the percentage of absorbed doses in the longitudinal direction with the xyz-TCM mode compared to the z-TCM mode at the center of the phantom was almost the same as the percent ratio at the periphery of the phantom. Therefore, the effect of xyz-TCM was less pronounced with the female phantom, especially on the reduction of the breast dose. The increase of image noise at the level of the supraclavicular fossa (in the male phantom) and at the level of the diaphragm (both phantoms) could not be avoided with the use of TCM techniques.

Effects of pacemaker, implantable cardioverter-defibrillator, and left ventricular leads on CT-based attenuation correction.

UNLABELLED: CT-based attenuation correction (CTAC) of myocardial SPECT images has been becoming more popular--and the application of SPECT/CT increasing--because it prevents attenuation-induced image degradation. However, CTAC can be affected by overestimation of counts caused by metals. It is possible that pacemaker, left ventricle (LV), and implantable cardioverter-defibrillator (ICD) leads have an influence on myocardial SPECT findings. The present study investigated the impact of these leads on SPECT with CTAC. METHODS: Pacemaker, LV, and ICD leads were examined using a simple phantom and a cardiac phantom. The effects of metal artifacts from leads in high-resolution mode and ultra-high-resolution mode were assessed using a simple phantom. Images and polar maps were generated from the cardiac phantom. RESULTS: The pacemaker and LV leads essentially had no influence, whereas the ICD lead resulted in maximal (6%) overestimation in a study investigating which metals cause artifacts that affect CTAC. None of the leads seriously influenced CTAC when the cardiac phantom was used. CONCLUSION: Small pacemaker or ICD and LV leads will cause a slight overestimation, but CTAC should be used because it can correct attenuation of the inferior and anteroseptal walls on SPECT images.

Accuracy of measuring half- and quarter-value layers and appropriate aperture width of a convenient method using a lead-covered case in X-ray computed tomography.

Determination of the half-value layer (HVL) and quarter-value layer (QVL) values is not an easy task in x-ray computed tomography (CT), because a nonrotating x-ray tube must be used, which requires the assistance of service engineers. Therefore, in this study, we determined the accuracy of the lead-covered case method, which uses x-rays from a rotating x-ray tube, for measuring the HVL and QVL in CT. The lead-covered case was manufactured from polystyrene foam and a 4-mm thick lead plate. The ionizing chamber was placed in the center of the case, and aluminum filters were placed 15 cm above the aperture surface. Aperture widths of 1.0, 2.0, and 3.0 cm for a tube voltage of 110 kV and an aperture width of 2.0 cm for the tube voltages of 80 and 130 kV were used to measure exposure doses. The results of the HVL and QVL were compared with those of the conventional nonrotating method. A 2.0-cm aperture was believed to be adequate, because of its small differences in the HVL and QVL in the nonrotating method and its reasonable exposure dose level. When the 2.0-cm aperture was used, the lead-covered case method demonstrated slightly larger HVLs and QVLs (0.03-0.06 mm for the HVL and 0.2-0.4 mm for the QVL) at all the tube voltage settings. However, the differences in the effective energy were 0.1-0.3 keV; therefore, it could be negligible in an organ-absorbed dose evaluation and a quality assurance test for CT.

Evaluation of the effectiveness of X-ray protective aprons in experimental and practical fields.

Few practical evaluation studies have been conducted on X-ray protective aprons in workplaces. We examined the effects of exchanging the protective apron type with regard to exposure reduction in experimental and practical fields, and discuss the effectiveness of X-ray protective aprons. Experimental field evaluations were performed by the measurement of the X-ray transmission rates of protective aprons. Practical field evaluations were performed by the estimation of the differences in the transit doses before and after the apron exchange. A 0.50-mm lead-equivalent-thick non-lead apron had the lowest transmission rate among the 7 protective aprons, but weighed 10.9 kg and was too heavy. The 0.25 and 0.35-mm lead-equivalent-thick non-lead aprons differed little in the practical field of interventional radiology. The 0.35-mm lead apron had lower X-ray transmission rates and transit doses than the 0.25-mm lead-equivalent-thick non-lead apron, and each of these differences exceeded 8% in the experimental field and approximately 0.15 mSv/month in the practical field of computed tomography (p < 0.01). Therefore, we concluded that the 0.25-mm lead-equivalent-thick aprons and 0.35-mm lead apron are effective for interventional radiology operators and computed tomography nurses, respectively.

Artifacts caused by insufficient contrast medium filling during C-arm cone-beam CT scans: a phantom study.

We investigated artifacts due to late-arriving contrast medium (CM) during C-arm cone-beam computed tomography. We scanned a phantom filled with water or with 100, 50, or 5% v/v concentrations of CM and then virtually produced CM-delayed projection data by partially replacing the projection images. Artifacts as a function of concentration, percentage of filling time, and size and position of the filling area were assessed. In addition, we used an automatic power injector with different injection delays to inject CM during the scans. A decrease in filling times caused by a lag in CM arrival during the scan resulted in a decrease in pixel values, distortion of the filling area, and appearance of streak artifacts. Even a delay of approximately 20% in CM arrival in the total scan time resulted in obvious distortion of the filling area. The distortion and streak artifacts tended to worsen at higher CM concentrations. Use of a minimum CM concentration based on the purpose of the examination and constant filling at the target region are effective for avoiding these artifacts.

Adjustment of overestimated CT-based attenuation correction on bone SPECT/CT after hip-resurfacing arthroplasty.

UNLABELLED: SPECT/CT has made it possible to perform attenuation correction easily. However, CT-based attenuation correction (CTAC) is overestimated when metal is inside the body. The aim of this investigation was to create and test a new attenuation correction formula for CTAC that decreases the overestimation caused by an artificial femoral head and hip joint. METHODS: We tested the usefulness of the new formula in a phantom study. The phantom contained "bones" made from gypsum. The components were placed in the phantom, the point source was placed both near metal and away from metal, and the counts were compared to verify the usefulness of the new attenuation correction formula. The new formula included use of thresholds to prevent the overestimation caused by proximity to metal. RESULTS: With the standard formula, the maximum overestimation was 18% for a 22-cm artificial hip joint placed in the acetabular roof. With the new formula, using 2 thresholds, the overestimation decreased to 4%. CONCLUSION: The new attenuation correction formula helps provide more correct data in SPECT/CT examinations of patients with metallic implants.