Terry T. Yoshizumi

Effective Doses in Radiology and Diagnostic Nuclear Medicine: A Catalog

Medical uses of radiation have grown very rapidly over the past decade, and, as of 2007, medical uses represent the largest source of exposure to the U.S. population. Most physicians have difficulty assessing the magnitude of exposure or potential risk. Effective dose provides an approximate indicator of potential detriment from ionizing radiation and should be used as one parameter in evaluating the appropriateness of examinations involving ionizing radiation. The purpose of this review is to provide a compilation of effective doses for radiologic and nuclear medicine procedures. Standard radiographic examinations have average effective doses that vary by over a factor of 1000 (0.01-10 mSv). Computed tomographic examinations tend to be in a more narrow range but have relatively high average effective doses (approximately 2-20 mSv), and average effective doses for interventional procedures usually range from 5-70 mSv. Average effective dose for most nuclear medicine procedures varies between 0.3 and 20 mSv. These doses can be compared with the average annual effective dose from background radiation of about 3 mSv.

Radiologic and Nuclear Medicine Studies in the United States and Worldwide: Frequency, Radiation Dose, and Comparison with Other Radiation Sources—1950–2007

The U.S. National Council on Radiation Protection and Measurements and United Nations Scientific Committee on Effects of Atomic Radiation each conducted respective assessments of all radiation sources in the United States and worldwide. The goal of this article is to summarize and combine the results of these two publicly available surveys and to compare the results with historical information. In the United States in 2006, about 377 million diagnostic and interventional radiologic examinations and 18 million nuclear medicine examinations were performed. The United States accounts for about 12% of radiologic procedures and about one-half of nuclear medicine procedures performed worldwide. In the United States, the frequency of diagnostic radiologic examinations has increased almost 10-fold (1950-2006). The U.S. per-capita annual effective dose from medical procedures has increased about sixfold (0.5 mSv [1980] to 3.0 mSv [2006]). Worldwide estimates for 2000-2007 indicate that 3.6 billion medical procedures with ionizing radiation (3.1 billion diagnostic radiologic, 0.5 billion dental, and 37 million nuclear medicine examinations) are performed annually. Worldwide, the average annual per-capita effective dose from medicine (about 0.6 mSv of the total 3.0 mSv received from all sources) has approximately doubled in the past 10-15 years.

Low-tube-voltage, high-tube-current multidetector abdominal CT: improved image quality and decreased radiation dose with adaptive statistical iterative reconstruction algorithm--initial clinical experience.

PURPOSE To investigate whether an adaptive statistical iterative reconstruction (ASIR) algorithm improves the image quality at low-tube-voltage (80-kVp), high-tube-current (675-mA) multidetector abdominal computed tomography (CT) during the late hepatic arterial phase. MATERIALS AND METHODS This prospective, single-center HIPAA-compliant study was institutional review board approved. Informed patient consent was obtained. Ten patients (six men, four women; mean age, 63 years; age range, 51-77 years) known or suspected to have hypervascular liver tumors underwent dual-energy 64-section multidetector CT. High- and low-tube-voltage CT images were acquired sequentially during the late hepatic arterial phase of contrast enhancement. Standard convolution FBP was used to reconstruct 140-kVp (protocol A) and 80-kVp (protocol B) image sets, and ASIR (protocol C) was used to reconstruct 80-kVp image sets. The mean image noise; contrast-to-noise ratio (CNR) relative to muscle for the aorta, liver, and pancreas; and effective dose with each protocol were assessed. A figure of merit (FOM) was computed to normalize the image noise and CNR for each protocol to effective dose. Repeated-measures analysis of variance with Bonferroni adjustment for multiple comparisons was used to compare differences in mean CNR, image noise, and corresponding FOM among the three protocols. The noise power spectra generated from a custom phantom with each protocol were also compared. RESULTS When image noise was normalized to effective dose, protocol C, as compared with protocols A (P = .0002) and B (P = .0001), yielded an approximately twofold reduction in noise. When the CNR was normalized to effective dose, protocol C yielded significantly higher CNRs for the aorta, liver, and pancreas than did protocol A (P = .0001 for all comparisons) and a significantly higher CNR for the liver than did protocol B (P = .003). Mean effective doses were 17.5 mSv +/- 0.6 (standard error) with protocol A and 5.1 mSv +/- 0.3 with protocols B and C. Compared with protocols A and B, protocol C yielded a small but quantifiable noise reduction across the entire spectrum of spatial frequencies. CONCLUSION Compared with standard FBP reconstruction, an ASIR algorithm improves image quality and has the potential to decrease radiation dose at low-tube-voltage, high-tube-current multidetector abdominal CT during the late hepatic arterial phase.

MEDICAL RADIATION EXPOSURE IN THE U.S. IN 2006 : PRELIMINARY RESULTS

Medical radiation exposure of the U.S. population has not been systematically evaluated for almost 25 y. In 1982, the per capita dose was estimated to be 0.54 mSv and the collective dose 124,000 person-Sv. The preliminary estimates of the NCRP Scientific Committee 6-2 medical subgroup are that, in 2006, the per capita dose from medical exposure (not including dental or radiotherapy) had increased almost 600% to about 3.0 mSv and the collective dose had increased over 700% to about 900,000 person-Sv. The largest contributions and increases have come primarily from CT scanning and nuclear medicine. The 62 million CT procedures accounted for 15% of the total number procedures (excluding dental) and over half of the collective dose. Nuclear medicine accounted for about 4% of all procedures but 26% of the total collective dose. Medical radiation exposure is now approximately equal to natural background radiation.

Radiation Doses from Small-Bowel Follow-Through and Abdominopelvic MDCT in Crohn's Disease

OBJECTIVE The purpose of our study was to compare organ and effective doses for small-bowel follow-through (SBFT) and abdominopelvic MDCT in adults with Crohns disease, to retrospectively evaluate the number of radiographic examinations performed for Crohns disease indications, and to identify those patients undergoing serial examinations to better delineate the use of radiology in the diagnosis and clinical management of Crohns disease. MATERIALS AND METHODS Using an anthropomorphic phantom and metal-oxide semiconductor field-effect transistor (MOSFET) dosimeters, specific organ doses were measured for 5 minutes of continuous fluoroscopy (kVp, 120; mA, 0.6) of each of the following: right lower quadrant, central abdomen, and pelvis. Effective doses were determined based on International Commission on Radiological Protection (ICRP) 60 weighting factors. Organ and effective doses were determined for abdominal and pelvic 16-MDCT: detector configuration, 16 x 0.625 mm; pitch, 1.75; 17.5 mm per rotation; rotation time, 0.5 second; 140 kVp; 340 mA. Electronic records were reviewed to determine the number of patients imaged for Crohns disease indications and the number of studies per patient. RESULTS The highest fluoroscopic organ doses were as follows: in the right lower quadrant, right kidney (0.78 cGy) and marrow (0.66 cGy); in the central abdomen, kidneys (1.5 and 1.6 cGy) and marrow (0.76 cGy); and in the pelvis, marrow (0.67-0.95 cGy). Effective doses for the right lower quadrant, central abdomen, and pelvis were 1.37, 2.02, and 3.83 mSv, respectively. For MDCT, the highest organ doses were to the liver (2.95-3.33 cGy). The effective dose for abdominopelvic MDCT was 16.1 mSv. Three hundred seventy-three patients underwent imaging for Crohns disease. The average number of SBFT and CT examinations was 1.8 and 2.3, respectively. Thirty-four (9%) of 373 patients underwent more than five CT examinations and 11 (3%) had more than 10. CONCLUSION Organ and effective doses are up to five times higher with MDCT than with SBFT. Crohns disease is more frequently imaged with CT. For a subset of patients who undergo numerous CT examinations, efforts should be made to minimize the number of CT examinations, decrease the CT dose, or consider MR enterography.

Radiation Dose Savings for Adult Pulmonary Embolus 64-MDCT Using Bismuth Breast Shields, Lower Peak Kilovoltage, and Automatic Tube Current Modulation

OBJECTIVE The purpose of this study was to assess whether radiation dose savings using a lower peak kilovoltage (kVp) setting, bismuth breast shields, and automatic tube current modulation could be achieved while preserving the image quality of MDCT scans obtained to assess for pulmonary embolus (PE). MATERIALS AND METHODS CT angiography (CTA) examinations were performed to assess for the presence or absence of pulmonary artery emboli using a 64-MDCT scanner with automatic tube current modulation (noise level=10 HU), two kVp settings (120 and 140 kVp), and bismuth breast shields. Absorbed organ doses were measured using anthropomorphic phantoms and metal oxide semiconductor field effect transistor (MOSFET) detectors. Image quality was assessed quantitatively as well as qualitatively in various anatomic sites of the thorax. RESULTS Using a lower kVp (120 vs 140 kVp) and automatic tube current modulation resulted in a dose savings of 27% to the breast and 47% to the lungs. The use of a lower kVp (120 kVp), automatic tube current modulation, and bismuth shields placed directly on the anterior chest wall reduced absorbed breast and lung doses by 55% and 45%, respectively. Qualitative assessment of the images showed no change in image quality of the lungs and mediastinum when using a lower kVp, bismuth shields, or both. CONCLUSION The use of bismuth breast shields together with a lower kVp and automatic tube current modulation will reduce the absorbed radiation dose to the breast and lungs without degradation of image quality to the organs of the thorax for CTA detection of PE.

Pediatric Chest MDCT Using Tube Current Modulation: Effect on Radiation Dose with Breast Shielding

OBJECTIVE The purpose of our study was to assess the effect on radiation dose and image noise during pediatric chest 16-MDCT using automatic tube current modulation and bismuth breast shields. MATERIALS AND METHODS Age-based chest 16-MDCT was performed on an anthropomorphic phantom representing a 5-year-old child. Two scans were obtained in each of four sequences: first, without a shield; second, with a 2-ply bismuth shield; third, using automatic tube current modulation with a scout image obtained after placement of the shield; and fourth, using automatic tube current modulation with a scout image obtained before placement of the shield. Metal oxide semiconductor field effect transistor technology was used to measure the radiation dose in 20 organ locations. Effective dose was estimated using the console dose-length product. Noise was measured by recording the SD of Hounsfield units in identical regions of interest. RESULTS The bismuth breast shield reduced the dose to the breast by 26%. Shielding and automatic tube current modulation reduced the breast dose by 52%. Multiple organ doses were lowest when the shield was placed after the scout radiograph had been obtained. When the shield was placed after the scout image was obtained, the mean noise in the range of shielding increased from 11.4 to 13.1 H (superior mediastinum) and from 10.0 to 12.8 H (heart) (p < 0.01). Increased noise, however, was near the target noise index (measured in SD of Hounsfield units) of 12.0 H (SD). Using automatic tube current modulation, the effective dose was reduced by 35% when the shield was placed after the scout and by 20% when the shield was present in the scout. CONCLUSION The greatest dose reduction is achieved by placing the shield after obtaining the scout image to avoid Auto mA compensation due to density of shield. With this technique, image noise increased but remained close to the target noise index.

Detection of Pancreatic Tumors, Image Quality, and Radiation Dose during the Pancreatic Parenchymal Phase: Effect of a Low-Tube-Voltage, High-Tube-Current CT Technique—Preliminary Results

PURPOSE To intraindividually compare a low-tube-voltage (80 kVp), high-tube-current (675 mA) computed tomographic (CT) technique with a high-tube-voltage (140 kVp) CT protocol for the detection of pancreatic tumors, image quality, and radiation dose during the pancreatic parenchymal phase. MATERIALS AND METHODS This prospective, single-center, HIPAA-compliant study was approved by the institutional review board, and written informed consent was obtained. Twenty-seven patients (nine men, 18 women; mean age, 64 years) with 23 solitary pancreatic tumors underwent dual-energy CT. Two imaging protocols were used: 140 kVp and 385 mA (protocol A) and 80 kVp and 675 mA (protocol B). For both protocols, the following variables were compared during the pancreatic parenchymal phase: contrast enhancement for the aorta, the pancreas, and the portal vein; pancreas-to-tumor contrast-to-noise ratio (CNR); noise; and effective dose. Two blinded, independent readers qualitatively scored the two data sets for tumor detection and image quality. Random-effect analysis of variance tests were used to compare differences between the two protocols. RESULTS Compared with protocol A, protocol B yielded significantly higher contrast enhancement for the aorta (508.6 HU vs 221.5 HU, respectively), pancreas (151.2 HU vs 67.0 HU), and portal vein (189.7 HU vs 87.3 HU), along with a greater pancreas-to-tumor CNR (8.1 vs 5.9) (P < .001 for all comparisons). No statistically significant difference in tumor detection was observed between the two protocols. Although standard deviation of image noise increased with protocol B (11.5 HU vs 18.6 HU), this protocol significantly reduced the effective dose (from 18.5 to 5.1 mSv; P < .001). CONCLUSION A low-tube-voltage, high-tube-current CT technique has the potential to improve the enhancement of the pancreas and peripancreatic vasculature, improve tumor conspicuity, and reduce patient radiation dose during the pancreatic parenchymal phase.

Radiation Dose to the Female Breast from 16-MDCT Body Protocols

OBJECTIVE The objective of our study was to determine the radiation dose to the female breast from current 16-MDCT body examinations. MATERIALS AND METHODS Metal oxide semiconductor field effect transistor (MOSFET) detectors were placed in four quadrants of the breast of a female-configured anthropomorphic phantom to determine radiation dose to the breast. Imaging was performed on a 16-MDCT scanner (LightSpeed, GE Healthcare) using current clinical protocols designed to assess pulmonary embolus (PE) (140 kVp, 380 mA, 0.8-sec rotation, 16 x 1.25 mm collimation), appendicitis (140 kVp, 340 mA, 0.5-sec rotation, 16 x 0.625 mm collimation), and renal calculus (140 kVp, 160 mA, 0.5-sec rotation, 16 x 0.625 mm collimation). RESULTS Radiation dose to the breast ranged from 4 to 6 cGy for the PE protocol and up to 1-2 cGy in the inferior aspect of the right breast and lateral aspect of the left breast for the appendicitis protocol. The renal calculus protocol yielded less than 150 microGy absorbed breast dose. CONCLUSION Current clinical chest and abdomen protocols result in vairable radiation doses to the breast. The magnitude of exposure may have implications for imaging strategies.

Pediatric cardiac-gated CT angiography : Assessment of radiation dose

OBJECTIVE The purpose of our study was to determine a dose range for cardiac-gated CT angiography (CTA) in children. MATERIALS AND METHODS ECG-gated cardiac CTA simulating scanning of the heart was performed on an anthropomorphic phantom of a 5-year-old child on a 16-MDCT scanner using variable parameters (small field of view; 16 x 0.625 mm configuration; 0.5-second gantry cycle time; 0.275 pitch; 120 kVp at 110, 220, and 330 mA; and 80 kVp at 385 mA). Metal oxide semiconductor field effect transistor (MOSFET) technology measured 20 organ doses. Effective dose calculated using the dose-length product (DLP) was compared with effective dose determined from measured absorbed organ doses. RESULTS Highest organ doses included breast (3.5-12.6 cGy), lung (3.3-12.1 cGy), and bone marrow (1.7-7.6 cGy). The 80 kVp/385 mA examination produced lower radiation doses to all organs than the 120 kVp/220 mA examination. MOSFET effective doses (+/- SD) were as follows: 110 mA: 7.4 mSv (+/- 0.6 mSv), 220 mA: 17.2 mSv (+/- 0.3 mSv), 330 mA: 25.7 mSv (+/- 0.3 mSv), 80 kVp/385 mA: 10.6 mSv (+/- 0.2 mSv). DLP effective doses for diagnostic runs were as follows: 110 mA: 8.7 mSv, 220 mA: 19 mSv, 330 mA: 28 mSv, 80 kVp/385 mA: 12 mSv. DLP effective doses exceeded MOSFET effective doses by 9.7-17.2%. CONCLUSION Radiation doses for a 5-year-old during cardiac-gated CTA vary greatly depending on parameters. Organ doses can be high; the effective dose may reach 28.4 mSv. Further work, including determination of size-appropriate mA and image quality, is important before routine use of this technique in children.