Tomographic ventilation-perfusion lung scintigraphy in cardiopulmonary disease

Sammanfattning: Respiration relies, among other things, on the balance between regional ventilation and perfusion in the lungs. There are many cardiopulmonary diseases, such as pulmonary embolism (PE), chronic obstructive pulmonary disease (COPD) and left heart failure (LHF), which can affect respiration negatively. The diagnosis of PE, COPD and LHF follows separate diagnostic pathways. However, the symptoms that cause the patient to seek medical care are overlapping. This results in a diagnostic dilemma that is complicated by the fact that cardiopulmonary diseases often coexist. Ventilation and perfusion can be imaged with lung scintigraphy. Lung scintigraphy is primarily used to diagnose PE. The introduction of 3-dimensional tomographic lung scintigraphy (V/P SPECT) has resulted in an improved accuracy in the diagnosis of PE. Follow-up with V/P SPECT may lead to better individualization of PE treatment, but has not yet been evaluated. Changes in ventilation and perfusion are also found in COPD and LHF. V/P SPECT may have a clinical role in the diagnosis and characterization of COPD and LHF, but this has been insufficiently studied. Therefore, this thesis focuses on the potential role for V/P SPECT in the follow-up of PE and in the diagnosis and classification of LHF and COPD. In study I, we found that V/P SPECT can be used to diagnose LHF with a high positive predictive value. We developed an algorithm to objectively calculate perfusion gradients and found that an inverted gravitational gradient in the lungs is indicative of LHF. It was also shown that LHF was common among patients with suspected PE. In study II we compared ventilation studies performed with 99mTc-DTPA and 99mTc-Technegas, in patients with and without COPD. This study showed that 99mTc-Technegas, due to a more homogeneous distribution with less focal deposition and better peripheral penetration, should be regarded as the preferred radioaerosol in V/P SPECT studies. Study III indicated an additional value of V/P SPECT in the diagnosis of COPD. V/P SPECT could also be used to characterize the severity of COPD. In study IV, we found that restoration of regional perfusion after acute PE occurred during the first 3 months of treatment, but not thereafter. Follow-up after an episode of PE, using V/P SPECT, seems important since about 20% of the patients in the study had remaining perfusion defects at 3 months after diagnosis, although all were free from symptoms.