Case Author(s): Scott Winner, M.D. and Henry Royal, M.D. , 2/14/97 . Rating: #D3, #Q4

Diagnosis: Malfunctioning photomultiplier tube

Brief history:

The patient presented with dyspnea and tachypnea


Pulmonary perfusion images

View main image(pe) in a separate image viewer

View second image(pe). Flood source field uniformity image

Full history/Diagnosis is available below

Diagnosis: Malfunctioning photomultiplier tube

Full history:

As above.


Tc-99m MAA and Cobalt-57 flood source


On the anterior images, there appears to be a perfusion defect in the lateral aspect of the left lower lobe. On the left anterior oblique view, the perfusion defect has not changed in shape and now appears to be in the posterior aspect of the left lower lobe. On the LPO view, the defect appears to be in the posterior aspect of the right lower lobe. Note also that the defect always appears in the same location within the field of view.


The defect seen on the pulmonary perfusion study was an artifact. A field uniformity image was acquired and demonstrated a circular region of decreased activity in the periphery of the field of view. This appearance is typical for malfunction of a photomultiplier tube. Each photomultiplier tube is connected to a preamplifier and, if the preamplifier malfunctions, the same round defect will be seen on the field uniformity image. Because relatively small changes in field uniformity can alter the interpretation of clinical studies, it is imperative to perform field uniformity tests each day that the camera is used. Other causes of nonuniformity include fracture of the crystal, collimator defects, dirt on a photographic lens, and an asymmetric energy window. All of these causes of nonuniformity are readily distinguishable from an artifact from a malfunctioning PM tube.



Major teaching point(s):


Differential Diagnosis List

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ACR Codes and Keywords:

References and General Discussion of Perfusion (only) Scintigraphy (Anatomic field:Lung, Mediastinum, and Pleura, Category:Normal, Technique, Congenital Anomaly)

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Case number: pe006

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