Derek A. Fladeland

Thyroid Shields versus z-Axis Automatic Tube Current Modulation for Dose Reduction at Neck CT

PURPOSE To assess the effectiveness of in-plane bismuth thyroid shields and a z-axis automatic tube current modulation (ATCM) technique with respect to dose reduction and image noise in the thyroid and other regional tissues during neck computed tomography (CT). MATERIALS AND METHODS Because this was a phantom study, neither institutional review board approval nor HIPAA compliance was required. A female phantom, thyroid shields, and an eight-section CT scanner were used. Radiation dose was measured by using thermoluminescent dosimetry (TLD) chips placed in the phantoms thyroid, cervical bone marrow, and soft tissues. Scans were performed by using fixed tube current and a z-axis ATCM technique with and without shields. Image noise was quantified as the standard deviation of the attenuation value (in Hounsfield units) on CT images. RESULTS Thyroid dose was 76.9 mGy with an unshielded fixed tube current technique. Use of shields and ATCM reduced this dose to 44.7 mGy (42% reduction, P < .001) and 17.0 mGy (78% reduction, P < .001), respectively. The combination of shields and ATCM further reduced this dose to between 11.9 and 12.9 mGy (83%-85% reduction, P < .001), depending on the shields presence in the scout scan. ATCM resulted in minimized tube current throughout the neck, which reduced dose-length product across the entire scan volume by 60% (926 vs 368 mGy . cm). Thyroid bed noise was lowest (3.9 HU) during the fixed tube current technique without shields, with noise slightly higher (6.9 HU) with the unshielded ATCM technique (P < .001). Thyroid image noise was markedly higher when using shields (P < .001), with noise measuring between 74 and 113 HU for fixed tube current and ATCM scans. CONCLUSION z-Axis ATCM is more effective than shields at reducing thyroid radiation dose during neck CT. Shields combined with ATCM slightly further reduces dose; however, this is associated with higher image noise.

Lead versus Bismuth-Antimony Shield for Fetal Dose Reduction at Different Gestational Ages at CT Pulmonary Angiography

PURPOSE To compare the effective fetal dose reduction at different stages of gestation during maternal computed tomographic (CT) pulmonary angiography by using traditional lead apron and bismuth-antimony shields combined with limited z-axis and tube current. MATERIALS AND METHODS Phantom with gravid prosthesis, 0.5-mm lead, and two grades of bismuth-antimony shield was used. Thermoluminescent dosimeters (TLDs) measured radiation in the first- to third-trimester uterus. Fetal dose was determined for each gestation by using 100 kVp to the costophrenic angles (CPAs) with and without shielding for a total of 12 scans. Eight third-trimester scans were used to compare shields using 120 kVp to CPAs versus those using 100 kVp to the diaphragm. RESULTS Average fetal dose increased with gestation with use of 100 kVp to CPAs, from 0.11 mGy in first trimester to 0.50 mGy in third trimester. Average third-trimester unshielded fetal dose was reduced from 0.82 mGy by using 120 kVp to CPAs to 0.17 mGy (79%, P < .001) by using 100 kVp to the diaphragm. Lead apron reduced dose more than either of the bismuth-antimony shields (72%-79% vs 57%-81%) with use of 100 kVp to CPAs. Shields reduced the dose by 73% (lead), 62% (90% attenuation bismuth-antimony), and 72% (95% attenuation bismuth-antimony) (P < .01) at 120 kVp to CPAs. No significant difference between shields was demonstrated with 100 kVp to the diaphragm (P < .01). Maternal dose was 8.13 mSv at 120 kVp to CPAs, 4.90 mSv at 100 kVp to CPAs, and 4.02 mSv at 100 kVp to the diaphragm. CONCLUSION Reducing voltage and limiting z-axis is more effective than shields at reducing fetal dose. Shielding improves reduction with no significant difference between lead and bismuth-antimony shields when conservative scanning parameters are observed.

Fetal shielding combined with state of the art CT dose reduction strategies during maternal chest CT

PURPOSE Custom bismuth-antimony shields were previously shown to reduce fetal dose by 53% on an 8DR (detector row) CT scanner without dynamic adaptive section collimation (DASC), automatic tube current modulation (ATCM) or adaptive statistical iterative reconstruction (ASiR). The purpose of this study is to compare the effective maternal and average fetal organ dose reduction both with and without bismuth-antimony shields on a 64DR CT scanner using DASC, ATCM and ASiR during maternal CTPA. MATERIALS AND METHODS A phantom with gravid prosthesis and a bismuth-antimony shield were used. Thermoluminescent dosimeters (TLDs) measured fetal radiation dose. The average fetal organ dose and effective maternal dose were determined using 100 kVp, scanning from the lung apices to the diaphragm utilizing DASC, ATCM and ASiR on a 64DR CT scanner with and without shielding in the first and third trimester. Isolated assessment of DASC was done via comparing a new 8DR scan without DASC to a similar scan on the 64DR with DASC. RESULTS Average third trimester unshielded fetal dose was reduced from 0.22 mGy ± 0.02 on the 8DR to 0.13 mGy ± 0.03 with the conservative 64DR protocol that included 30% ASiR, DASC and ATCM (42% reduction, P<0.01). Use of a shield further reduced average third trimester fetal dose to 0.04 mGy ± 0.01 (69% reduction, P<0.01). The average fetal organ dose reduction attributable to DASC alone was modest (6% reduction from 0.17 mGy ± 0.02 to 0.16 mGy ± 0.02, P=0.014). First trimester fetal organ dose on the 8DR protocol was 0.07 mGy ± 0.03. This was reduced to 0.05 mGy ± 0.03 on the 64DR protocol without shielding (30% reduction, P=0.009). Shields further reduced this dose to below accurately detectable levels. Effective maternal dose was reduced from 4.0 mSv on the 8DR to 2.5 mSv on the 64DR scanner using the conservative protocol (38% dose reduction). CONCLUSION ASiR, ATCM and DASC combined significantly reduce effective maternal and fetal organ dose during CTPA. Shields continue to be an effective means of fetal dose reduction.

Radiation Dose from Diagnostic Computed Tomography in Saskatchewan

Objective To calculate the effective dose from diagnostic computed tomography (CT) scans in Saskatchewan, Canada, and compare with other reported dose levels. Methods Data from CT scans were collected from 12 scanners in 7 cities across Saskatchewan. The patient age, scan type, and selected technique parameters including the dose length product and the volume computed tomography dose index were collected for a 2-week period. This information then was used to calculate effective doses patients are exposed to during CT examinations. Data from 2,061 clinically indicated CT examinations were collected, and of them 1,690 were eligible for analysis. Every examination during a 2-week period was recorded without selection. Results The average provincial estimated patient dose was as follows: head, 2.7 mSv (638 scans; standard deviation [SD], ±1.6); chest, 11.3 mSv (376 scans; SD, ±8.9); abdomen-pelvis, 15.5 mSv (578 scans; SD, ±10.0); abdomen, 11.7 mSv (80 scans; SD, ±11.48), and pelvis, 8.6 mSv (18 scans; SD, ±6.04). Significant variation in dose between the CT scanners was observed (P = .049 for head, P = .001 for chest, and P = .034 for abdomen-pelvis). Conclusions Overall, the estimated dose from diagnostic CT examinations was similar to other previously published Canadian data from British Columbia. This dose varied slightly from some other published standards, including being higher than those found in a review conducted in the United Kingdom in 2003.

Normal Expiratory Flow Rate and Lung Volumes in Patients with Combined Emphysema and Interstitial Lung Disease: A Case Series and Literature Review

Pulmonary function tests in patients with idiopathic pulmonary fibrosis characteristically show a restrictive pattern including small lung volumes and increased expiratory flow rates resulting from a reduction in pulmonary compliance due to diffuse fibrosis. Conversely, an obstructive pattern with hyperinflation results in emphysema by loss of elastic recoil, expiratory collapse of the peripheral airways and air trapping. When the diseases coexist, pulmonary volumes are compensated, and a smaller than expected reduction or even normal lung volumes can be found. The present report describes 10 patients with progressive breathlessness, three of whom experienced severe limitation in their quality of life. All patients showed lung interstitial involvement and emphysema on computed tomography scan of the chest. The 10 patients showed normal spirometry and lung volumes with severe compromise of gas exchange. Normal lung volumes do not exclude diagnosis of idiopathic pulmonary fibrosis in patients with concomitant emphysema. The relatively preserved lung volumes may underestimate the severity of idiopathic pulmonary fibrosis and attenuate its effects on lung function parameters.

Changing Radiation Dose From Diagnostic Computed Tomography Examinations in Saskatchewan

Purpose Follow-up study to observe if provincial mean effective radiation dose for head, chest, and abdomen-pelvis (AP) computed tomographies (CTs) remained stable or changed since the initial 2006 survey. Methods Data were collected in July 2008 from Saskatchewans 13 diagnostic CT scanners of 3358 CT examinations. These data included the number of scan phases and projected dose length product (DLP). Technologists compared projected DLP with 2006 reference data before scanning. Projected DLP was converted to effective dose (ED) for each head, chest, and AP CT. The total dose that the patients received with scans of multiple body parts at the same visit also was determined. Results The mean (± SD) provincial ED was 3.4 ± 1.6 mSv for 1023 head scans (2.7 ± 1.6 mSv in 2006), 9.6 ± 4.8 mSv for 588 chest scans (11.3 ± 8.9 mSv in 2006), and 16.1 ± 9.9 mSv for 983 AP scans (15.5 ± 10.0 mSv in 2006). Single-phase multidetector row CT ED decreased by 31% for chest scans (9.5 ± 3.9 mSv vs 13.7 ± 9.7 mSv in 2006) and 17% for AP scans (13.9 ± 6.0 mSv vs 16.8 ± 10.6 mSv in 2006) and increased by 19% for head scans (3.2 ± 1.2 mSv vs 2.7 ± 1.5 mSv in 2006). The total patient dose was highest (33.8 ± 10.1 mSv) for the 20 patients who received head, neck, chest, and AP scans during a single visit. Because of increased utilisation and the increased CT head dose, Saskatchewan per capital radiation dose from CT increased by 21% between 2006 and 2008 (1.14 vs 1.38 mSv/person per year). Conclusion Significant dose and variation reduction was seen for single-phase CT chest and AP examinations between 2006 and 2008, whereas CT head dose increased over the same interval. These changes, combined with increased utilisation, resulted in per capita increase in radiation dose from CT between the 2 studies.

Familial Interstitial Pulmonary Fibrosis: A Large Family with Atypical Clinical Features

A large kindred of familial pulmonary fibrosis is reported. Six members from the first two generations of this particular kindred were described more than 40 years previously; six more individuals from the third and fourth generations have also been evaluated. The proband, now 23 years of age, has mild disease; the other 11 documented affected family members all died from their disease at an average age of 37 years (range 25 to 50 years). The pathology was that of usual interstitial pneumonia, as is typical in idiopathic pulmonary fibrosis. However, the initial radiographic pattern in many of these individuals was upper lobe and nodular and, along with the young age, was atypical for idiopathic pulmonary fibrosis. Several genetic abnormalities have been associated with familial pulmonary fibrosis. The present study examined the genes coding for surfactant protein-C, ATPbinding cassette protein A3 and telomerase, and found no abnormalities.

Are pretest clinical probability algorithms used before obtaining multidetector computed tomographic pulmonary embolism studies

Pulmonary embolism (PE) is a complex and important clinical entity that requires accurate and timely diagnosis and management. With the advent of multidetector computed tomography (MDCT) technology, the ability to perform imaging for the detection of PE during the pulmonary arterial phase of contrast enhancement became a reality. The advancement of this technology over the last decade has led to ever-increasing utilisation of this imaging modality in the acute care setting. The relatively high frequency of negative MDCT examinations for PE at our facility led us to suspect that our clinical colleagues may not be screening the patient population with clinical algorithms as effectively as possible. This suspicion, coupled with an emergency medical department communication that suggested that the revised Wells criteria, published in 2006 in the Journal of Thrombosis and Thrombolysis, should be used for pre-MDCT screening led us to investigate whether pretest clinical algorithms were being applied at our institution [1e3]. Current recommendations mandate that patients undergo D-dimer testing if there is a low pretest clinical probability of PE (Wells !4). A MDCT study or ventilation-perfusion lung scan should be pursued if the D-dimer result is positive, whereas a negative D-dimer result in this patient population has been shown to safely exclude PE [2e5]. Van Belle showed the 3 month incidence of PE in patients who had an unlikely Wells clinical probability score and negative D-dimer result to be 0.5% [5]. Patients with a high pretest probability of PE (Wells >4) should receive an MDCT or VQ scan, regardless of their D-dimer score [2e4]. Methods

A Posterior Pneumothorax

1Division of Respirology, Critical Care and Sleep Medicine, Department of Medicine; 2Department of Medical Imaging, University of Saskatchewan, Saskatoon, Saskatchewan Correspondence: Dr Julian S Tam, Division of Respirology, Critical Care and Sleep Medicine, Department of Medicine, University of Saskatchewan, 5th Floor Ellis Hall, 103 Hospital Drive, Saskatoon, Saskatchewan S7N 0W8. Telephone 306-966-8274, fax 306-966-8694, e-mail contact@juliantam.com A 60-year-old woman with interstitial lung disease was reviewed in clinic three weeks after undergoing a right lower lobe lung biopsy via video-assisted thoracoscopic surgery. Chest imaging studies had revealed bilateral reticular markings with peripheral and lower lung zone predominance. The pathology documented constrictive bronchiolitis and a usual interstitial pneumonia (UIP)-type fibrosing interstitial pneumonia. The patient described modest worsening of dyspnea on exertion and discomfort in her right-lower chest following her surgery; she attributed this to expected sequelae of surgery. The initial chest radiograph revealed lung markings extending to the chest wall, but increased radiolucency in the right base compared with previous. Shift of the heart to the left, depression of the right hemidiaphragm and an apparent prominent right hilum were also seen (Figure 1). On bedside right-sided chest ultrasonographic examination, positive sliding pleural and seashore signs were elicited anteriorly; posterior examination was significant for negative sliding pleural and positive barcode signs (1) (Figures 2 and 3, Videos 1 and 2 [click on the camera icons in the video legends on this page]). A computed tomography scan of the chest confirmed the diagnosis of a large, posterior right-sided pneumothorax (Figure 4). The patient was admitted to hospital and a chest tube was inserted. Her hospital admission was prolonged due to a persistent air leak. Following drainage of the pneumothorax, subsequent chest radiographs showed re-expansion of the right lung (Figure 5). imAges in respirAtory medicine

Hot tub lung: A tale of two manifestations

ABSTRACT Hot tub lung is a form of Mycobacterium avium complex (MAC)-associated pulmonary disease following exposure to contaminated hot tub water. Diagnosis is based on subacute symptoms, hot tub exposure, radiographic findings and MAC isolates in sputum, bronchoalveolar lavage fluid, biopsies and/or hot tub water. Management recommendations include avoidance of hot tubs, manufacturer recommended maintenance and consideration of corticosteroids and anti-mycobacterials on a case-by-case basis. We present here two distinct presentations of MAC-associated pulmonary disease from the same exposure, including one with a tracheal nodule showing granulomatous inflammation, which has not been previously described.