Taebong Chung

Imaging of Lung Transplantation: Review

OBJECTIVE Lung transplantation is an established treatment for end-stage pulmonary disease. Complications of lung transplantation include airway stenosis and dehiscence, reimplantation response, acute rejection, infection, posttransplantation lymphoproliferative disorder, and bronchiolitis obliterans syndrome. The incidence of graft rejection and airway anastomosis experienced in the early years of lung transplantation have been significantly reduced by advances in immunosuppression and surgical techniques. Infection is currently the most common cause of mortality during the first 6 months after transplantation, whereas chronic rejection or obliterative bronchiolitis is the most common cause of mortality thereafter. This article reviews the radiologic findings of different surgical techniques as well as the common early and late complications of lung transplantation. CONCLUSION Radiology plays a pivotal role in the diagnosis and management of complications of lung transplantation. Advancements in surgical technique and medical therapy influence the spectrum of expected radiologic findings. Familiarity with the radiologic appearances of common surgical techniques and complications of lung transplantation is important.

Dynamic Airway Evaluation with Volume CT: Initial Experience

Purpose The purpose of the study was to prospectively establish the use of a novel multidetector computed tomography unit (MDCT) with 320 × 0.5 detector rows for the evaluation of tracheomalacia by using a dynamic expiratory low-dose technique. Methods Six adult patients (5 men, 1 woman; mean age, 53.7 years [37–70 years]) referred for a clinical suspicion of tracheomalacia were studied on a 320-row MDCT unit by using the following parameters: 120 kVp, 40–50 mA, 0.5-second gantry rotation, and z-axis coverage of 160 mm sufficient to cover the thoracic trachea to the proximal bronchi. Image acquisition occurred during a forceful exhalation. The image data set was subject to the following analyses: cross-sectional area of airway lumen at 4 predefined locations (thoracic inlet, aortic arch, carina, and bronchus intermedius) and measurement of airway volume. Results All 6 patients had evidence of tracheomalacia, the proximal trachea collapsed at a later phase of expiration (3–4 seconds) than the distal trachea (2–3 seconds). The most common region of airway collapse occurred at the level of the aortic arch (5/6 [83%]), Three patients (50%) had diffuse segmental luminal narrowing that involved the tracheobronchial tree. The radiation dose (estimated dose length product, computed tomography console) measured 293.9 mGy in 1 subject and 483.5 mGy in 5 patients. Conclusions Four-dimensional true isophasic and isovolumetric imaging of the central airways by using 320-row MDCT is a viable technique for the diagnosis of tracheomalacia; it provides a comprehensive assessment of airways dynamic.

Chest low-dose computed tomography in neutropenic acute myeloid leukaemia patients.

BACKGROUND We aimed to compare chest low-dose computed tomography (LDCT) with chest radiography (CXR) in the assessment of febrile acute myeloid leukaemia neutropenic patients. METHODS A prospective non-randomized study was carried out between 30 May, 2003 and 3 June, 2004 in consecutive neutropenic patients who required imaging of the thorax and were treated for acute myeloid leukaemia. Each patient had a baseline 2-view chest radiograph followed by LDCT. Both the CXR and the LDCT studies were blindly and independently reviewed by two chest radiologists. RESULTS Forty patients were enrolled: 24 male and 16 female, mean age 53.5 years (range 18-83) and an average neutrophil count of 0.78 x 10(9)/L. Patients had CXR within a mean of 40 min from the LDCT. Overall, 31 (77.5%) of 40 CXR were abnormal, whereas LDCT detected abnormalities in 38 (95%) of 40 patients. LDCT demonstrated three times the number of lung nodules as CXR and twice as many ground-glass opacities. Lung consolidation was detected similarly using both techniques, but LDCT demonstrated more extensive and multi-focal consolidation. The majority of nodules detected only on LDCT were subcentimetre in diameter. The additional information provided by LDCT led to an alteration in the clinical management of 11 (27.5%) of 40 patients. CONCLUSION LDCT is a useful tool in the initial investigation of suspected pulmonary complication in neutropenic patients. This is supported by the additional information it provides to the CXR with reduced radiation when compared to conventional CT.

Investigating the low-dose limits of multidetector CT in lung nodule surveillance

The purpose of this study was to evaluate the factors limiting nodule detection in thoracic computed tomography (CT) and to determine whether prior knowledge of nodule size and attenuation, available from a baseline CT study, influences the minimum radiation dose at which nodule surveillance CT scans can be performed while maintaining current levels of nodule detectability. Multiple nodules varying in attenuation (-509 to + 110 HU) and diameter (1.6 to 9.5 mm) were layered in random and ordered sequences within 2 lung cylinders made of Rando lung material and suspended within a custom-built CT phantom. Multiple CT scans were performed at varying kVp (120, 100, and 80), mA (200, 150, 100, 50, 20, and 10), and beam collimation (5, 2.5, and 1.25 mm) on a four-row multidetector scanner (Lightspeed, General Electric, Milwaukee, WI) using 0.8 s gantry rotation. The corresponding range of radiation dose over which images were acquired was 0.3-26.4 mGy. Nine observers independently performed three specific tasks, namely: (1) To detect a 3.2 mm nodule of 23 HU; (2) To detect 3.2 mm nodules of varying attenuation (-509 to -154 HU); and (3) To detect nodules varying in size (1.6-9 mm) and attenuation (-509 to 110 HU). A two-alternative forced-choice test was used in order to determine the limits of nodule detection in terms of the proportion of correct responses (Pcorr, related to the area under the ROC curve) as a summary metric of observer performance. The radiation dose levels for detection of 99% of nodules in each task were as follows: Task 1 (1 mGy); Task 2 (5 mGy); and Task 3 (7 mGy). The corresponding interobserver confidence limits were 1, 5, and 10 mGy for Tasks 1, 2, and 3, respectively. There was a fivefold increase in the radiation dose required for detection of lower-density nodules (Tasks 1 to 2). Absence of prior knowledge of the nodule size and density (Task 3) corresponds to a significant increase in the minimum required radiation dose. Significant image degradation and reduction in observer performance for all tasks occur at a dose of < or = 1 mGy. It is concluded that the size and attenuation of a nodule strongly influence the radiation dose required for confident evaluation with a minimum threshold value of 1-2 mGy (minimum dose CT). A prior knowledge of nodule size and attenuation is available from the baseline CT scan and is an important consideration in minimizing the radiation exposure required for nodule detection with surveillance CT.

Imaging of Lung Transplantation: Self-Assessment Module

ObjectiveThe educational objectives of this continuing medical education activity are for the reader to exercise, self-assess, and improve skills in diagnostic radiology with regard to imaging of lung transplantation and to improve familiarity with the complications of lung transplantation.ConclusionThe articles in this activity review the imaging and complications of lung transplantation and discuss the role of imaging in the assessment of complications from lung transplantation.