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

Pulmonary Functional Imaging: Part 1-State-of-the-Art Technical and Physiologic Underpinnings

Over the past few decades, pulmonary imaging technologies have advanced from chest radiography and nuclear medicine methods to high-spatial-resolution or low-dose chest CT and MRI. It is currently possible to identify and measure pulmonary pathologic changes before these are obvious even to patients or depicted on conventional morphologic images. Here, key technological advances are described, including multiparametric CT image processing methods, inhaled hyperpolarized and fluorinated gas MRI, and four-dimensional free-breathing CT and MRI methods to measure regional ventilation, perfusion, gas exchange, and biomechanics. The basic anatomic and physiologic underpinnings of these pulmonary functional imaging techniques are explained. In addition, advances in image analysis and computational and artificial intelligence (machine learning) methods pertinent to functional lung imaging are discussed. The clinical applications of pulmonary functional imaging, including both the opportunities and challenges for clinical translation and deployment, will be discussed in part 2 of this review. Given the technical advances in these sophisticated imaging methods and the wealth of information they can provide, it is anticipated that pulmonary functional imaging will be increasingly used in the care of patients with lung disease. © RSNA, 2021 Online supplemental material is available for this article.

Overview of the Novel and Improved Pulmonary Ventilation-Perfusion Imaging Applications in the Era of SPECT/CT

OBJECTIVE

In this article, we describe the concepts of ventilation-perfusion planar, SPECT, and SPECT/CT and outline the advantages of integrated ventilation-perfusion SPECT/CT over planar imaging. We present an overview of the traditional and new applications of ventilation-perfusion scintigraphy.

CONCLUSION

SPECT/CT has improved the diagnostic accuracy of ventilation-perfusion imaging and opened the door for a new spectrum of applications.

Oxygen-enhanced MRI, thin-section MDCT, and perfusion SPECT/CT: comparison of clinical implications to patient care for lung volume reduction surgery

OBJECTIVE

The purpose of our study was to prospectively and directly compare capability of O2-enhanced MRI, MDCT, and perfusion SPECT/CT to clinical outcome measurements in candidates for lung volume reduction surgery (LVRS).

SUBJECTS AND METHODS

Twenty-five consecutive candidates for LVRS (20 men and five women; age range, 45-76 years) underwent MDCT, O2-enhanced MRI, and perfusion SPECT/CT before and after LVRS. Clinical outcomes for each candidate were evaluated in terms of differences between pre- and postoperative percentage forced expiratory volume in 1 second (%FEV1), Pao2, and 6-minute walking distance. Quantitatively assessed upper/lower lung ratios on O2-enhanced MRI, MDCT, and SPECT/CT were calculated from regional relative enhancement ratios, functional lung volumes, and radioisotope uptakes between upper and lower lungs. Qualitatively assessed upper/lower lung ratios on O2-enhanced MRI, MDCT, and SPECT/CT were estimated using visual scoring systems. To evaluate the correlation for individual upper/lower lung ratios and clinical outcomes, all upper/lower lung ratios were correlated with clinical outcomes. Improvements in mean relative enhancement ratio were directly correlated with clinical outcomes to assess the capability of O2-enhanced MRI to assess therapeutic effect.

RESULTS

All quantitatively (-0.63≤r≤-0.47, p<0.05) and qualitatively (0.41≤r≤0.57, p<0.05) assessed upper/lower lung ratios showed moderate and statistically significant correlation with clinical outcomes, and improvement in mean relative enhancement ratio showed moderate or good correlation, both statistically significant (-0.44≤r≤0.71, p<0.05).

CONCLUSION

O2-enhanced MRI shows potential for more accurate evaluation of postoperative clinical outcome for LVRS candidates than SPECT/CT and can be considered at least as reliable as MDCT.

Less commonly used and emerging clinical applications of SPECT-CT in benign and malignant disease

The emergence of hybrid imaging, combining anatomical computed tomography (CT) and functional single-photon emission computed tomography (SPECT), has greatly expanded the armoury available to image disease. Integrated SPECT-CT is a dual-modality technique, which improves the sensitivity and specificity of existing radionuclide studies and enables characterization of equivocal findings detected by conventional imaging. There is a wide range of established and emerging clinical applications for SPECT-CT, which were reviewed in detail at a symposium organized by the British Institute of Radiology in March 2012. A series of articles were commissioned as an adjunct to the symposium and to raise awareness of the clinical utility of this technique. The focus of this article is on less commonly used and emerging clinical applications of hybrid SPECT-CT in a spectrum of benign and malignant conditions. The article will illustrate the incremental value of the technique in a variety of clinical applications.

V/Q SPECT: utility for investigation of pulmonary physiology

Single-photon emission computed tomography (SPECT) is being increasingly used as a tool in respiratory research, in particular ventilation SPECT. Much of the basic understanding of pulmonary physiology has been derived from inhaled radioactive inert gases because, as the lung behaves in an asymmetric manner, the nature of regional differences in ventilation is ideally studied with the use of imaging. It is well known to clinicians that ventilation is patchy in patients who have airways disease. However, the relevance to the disease mechanisms itself only started to be studied with the use of 3-dimensional imaging and with advances in quantitative image analysis. The measurements of both ventilation distribution and nonventilation (airway closure) have become very topical in the study of asthma, and accurate quantification of those parameters is of relevance to disease mechanisms. In chronic obstructive pulmonary disease, the drive is towards better characterization of disease groups ("phenotypes") and, again, description of ventilation patterns may prove to be useful. This is a review, therefore, on pulmonary SPECT imaging in respiratory research which includes a focus on methodology in relation to respiratory physiology. There has been relatively little published in this area but there is great potential for advances in the understanding of airways disease to be gained from SPECT imaging.