Co-registered perfusion SPECT/CT: Utility for prediction of improved postoperative outcome in lung volume reduction surgery candidates

Abstract

Purpose

To directly compare the capabilities of perfusion scan, SPECT, co-registered SPECT/CT, and quantitatively and qualitatively assessed MDCT (i.e. quantitative CT and qualitative CT) for predicting postoperative clinical outcome for lung volume reduction surgery (LVRS) candidates.

Materials and methods

Twenty-five consecutive candidates (19 men and six women, age range: 42–72 years) for LVRS underwent preoperative CT and perfusion scan with SPECT. Clinical outcome of LVRS for all subjects was also assessed by determining the difference between pre- and postoperative forced expiratory volume in 1 s (FEV₁) and 6-min walking distance (6MWD). All SPECT examinations were performed on a SPECT scanner, and co-registered to thin-section CT by using commercially available software. On planar imaging, SPECT and SPECT/CT, upper versus lower zone or lobe ratios (U/Ls) were calculated from regional uptakes between upper and lower lung fields in the operated lung. On quantitatively assessed CT, U/L for all subjects was assessed from regional functional lung volumes. On qualitatively assessed CT, planar imaging, SPECT and co-registered SPECT/CT, U/Ls were assessed with a 4-point visual scoring system. To compare capabilities of predicting clinical outcome, each U/L was statistically correlated with the corresponding clinical outcome.

Results

Significantly fair or moderate correlations were observed between quantitatively and qualitatively assessed U/Ls obtained with all four methods and clinical outcomes (−0.60 ≤ r ≤ −0.42, p < 0.05).

Conclusion

Co-registered perfusion SPECT/CT has better correlation with clinical outcome in LVRS candidates than do planar imaging, SPECT or qualitatively assessed CT, and is at least as valid as quantitatively assessed CT.

Introduction

Pulmonary emphysema is a chronic obstructive pulmonary disease, which is associated with smoking, and more common in men than women, although its incidence in women is rising. Medical treatment for emphysema is supportive and includes corticosteroids, bronchodilators, pulmonary rehabilitation, supplemental oxygen and cessation of smoking [1]. However, for severe emphysema lung transplantation is a treatment option with proven therapeutic utility, although it is not in wide enough use to benefit the majority of patients requiring treatment [2]. In addition, transplantation may be followed by significant morbidity and mortality secondary to long-term immunosuppressive therapy and chronic allograft rejection [3], [4]. Therefore, lung volume reduction surgery (LVRS) is another technique being evaluated for management of severe emphysema patients. The excision of non-functional lung tissue in LVRS is believed to improve lung function by relieving compression on normal underlying lung tissue, and enhance lung elastic recoil which permits outward forces to restore collapsed bronchioles [5], [6], [7], [8].

Patients with upper lobe predominant emphysema show a better outcome after LVRS than patients with diffuse disease [9]. In addition, clinicians are frequently asked to evaluate the distribution of disease, especially for low-risk patients, by using the results of the National Emphysema Treatment Trial (NETT) [10], [11]. Currently, most patients evaluated for LVRS undergo preoperative radiologic imaging including chest radiograph, quantitatively and qualitatively assessed computed tomography (CT), and ventilation and/or perfusion scintigraphy or single-photon emission tomography (SPECT) for assessment of disease extent, severity and distribution [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23]. This information is utilized for identification of potential candidates for LVRS and decisions regarding surgical procedures. In addition, radiologic information combined with physiologic studies may serve as predictors of positive and negative outcomes [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23].

Recently, it has become possible to fuse data sets obtained from different modalities. A few investigators have suggested that co-registered (or fused) SPECT and CT imaging (SPECT/CT) may be effective for assessment of regional pulmonary functional impairment in patients with pulmonary emphysema, pulmonary thromboembolism and lung cancer [24], [25], [26], [27].

We hypothesized that co-registered perfusion SPECT/CT may result in more accurate assessment of extent, severity and distribution of emphysema than is possible with quantitatively and qualitatively assessed multi-detector row CT and perfusion SPECT or planar imaging. The purpose of the study presented here was thus to prospectively compare the predictive capability of co-registered SPECT/CT for postoperative outcome for LVRS candidates as compared with quantitatively and qualitatively assessed CT, planar imaging and SPECT.