Lung perfusion scan

M.B. Use of macroaggregated albumin lung perfusion scan to diagnose hepatopulmonary syndrome a new approach. Gastroenterology 1998 114 305-310... 

Jeffrey, G.R, Prince, R.L., van der Schaaf, A. Fatal intrapulmonary arteriovenous shunting in cirrhosis diagnosis by radionuclide lung perfusion scan. Med. J. Aust. 1990 152 549-553... 

Figure 3. Lung perfusion anterior scan using Kr-81m. Top, supine bottom, upright. (Photo courtesy of Drs. Matthew Horn and Kathryn Witztum, VA Medical Center, University of California, San Diego.)...

Figure 14 Planar anterior and posterior images obtained following inhalation of two different-size pMDI aerosols, with the outline of the lung drawn from the anterior and posterior perfusion scans. The difference in geometry and distribution of deposited radioactivity between the anterior and posterior images reflects the proximity of that area of the lung to the gamma camera face.

For example, when using a perfusion scan to outline the lung and to correct for tissue attenuation of radioactivity, the total lung dose deposited (TLDrf) is calculated as follows ... 

Taplin GV, Chopra SK (1978) Lung perfusion-inhalation scintigraphy in obstructive airway disease and pulmonary embolism. Radiol Clin N Am 16 491-513 Taplin GV, MacDonald NS (1971) Radiochemistry of macroaggregated albumin and newer lung scanning agents. Sem Nucl Med 1 132-152... 

The main diagnostic practices with radiopharmaceuticals are the procedures for bone, cardiovascular, lung perfusion, lung ventilation, thyroid scan, thyroid uptake, renal, liver/ spleen, and brain examinations. The effective doses per procedure are considerably higher and are 4.5 mSv, 8 mSv, 1.5 mSv, 1 mSv, 3.4 mSv, 15 mSv, 1.9 mSv, 1.7 mSv, and 6 mSv, respectively, and the number of procedures per 1,000 population are 4.5, 2.7, 1.8, 0.34, 4.1, 0.92, 0.89, 2.1, and 1.3, respectively for countries at health-care level I. But patients near to the end of their lives receive many of these exposures, and thus the doses are not distributed evenly among the population. Therefore, these doses should not be used for the assessment of detrimental effects of radiation exposure. 

Fig. 2. Right posterior obHque lung or V/Q scan of a 65-year-old man presented with acute onset of shortness of breath and pleuritic chest pain (pain with breathing), (a) The perfusion lung scan showing defects in both the right upper lobe (arrow) and in the right lower lobe (arrowheads), (b) The ventilation...

Ventilation-perfusion (V/Q) and computed tomographic (CT) scans are the most commonly used tests to diagnosis PE. A V/Q scan measures the distribution of blood and airflow in the lungs. When there is a large mismatch between blood and airflow in one area of the lung, there is a high probability that the patient has a PE. Spiral CT scans can detect emboli in the pulmonary arteries. 

Perfusion lung scanning was performed with a rectilinear scanner, built at Johns Hopkins and modeled on the scanner invented by Ben Cassen. 

With the advent of MDCT, axial step-and-shoot scanning has remained in use for only few clinical ap-phcations, such as head scanning, high-resolution lung scanning, perfusion CT and interventional applications. A detailed theoretical description to predict the performance of MDCT in step-and-shoot mode has been given (Hsieh 2001). 

This approach can be used to extract further clinically relevant information from CT scans acquired at normal dose levels. For example, it is possible to identify iodine in liver or kidney tissue and to display the contrast enhancement either by colorcoding it in the CT image or by subtracting it to obtain virtual unenhanced images. This also works in lung tissue for the evaluation of pulmonary perfusion. Also, bones can be eliminated from angiography datasets by the spectral properties of calcium so that the evaluation of vessels becomes easier and faster in a maximum intensity projection. Applications without contrast material include the differentiation of kidney stones and the depiction of tendons and ligaments. 

Fig. 1. Scanning electron micrograph of the perfusion-fixed lung tissue (Weibel, 1984), showing transition between peripheral bronchiole (BL) and terminal bronchiole (T). Alveolar ducts are denoted by arrows in the direction of downstream flow, near pulmonary arteries (A) and veins (V). Scale marker is 200 jim.

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