Enhancing Lung Scintigraphy With Single-Photon Emission Computed Tomography

Ventilation-perfusion scan for diagnosing pulmonary embolism: do chest x-rays matter?

BACKGROUND

Ventilation-perfusion (V/Q) scan coupled with single photon emission computed tomography (SPECT) is commonly used for the diagnosis of pulmonary embolism (PE). An abnormal chest x-ray (CXR) is deemed to hinder the interpretation of V/Q scan and therefore a normal CXR is recommended prior to V/Q scan.

AIMS

To determine if an abnormal CXR impacted on V/Q scan interpretation and subsequent management.

METHODS

A retrospective cohort analysis of all patients who underwent a V/Q scan for diagnosis of suspected acute PE between March 2016 and 2022 was performed. CXR reports were reviewed and classified as normal or abnormal. Low-dose computerised tomography was routinely performed in patients above the age of 70. Data regarding V/Q scan results and subsequent management including initiation of anticoagulation for PE or further diagnostic investigations were collected.

RESULTS

A total of 340 cases were evaluated. Of the positive V/Q scans (92/340), 98.3% of the normal CXR were anticoagulated compared to 100% of the abnormal CXR group. Of the negative V/Q scans (239/340), no cases were started on anticoagulation and no further investigations were performed across both normal and abnormal CXR groups. Indeterminate results occurred in only 9 cases with no significant difference in management between normal and abnormal CXR groups.

CONCLUSION

An abnormal CXR does not affect the reliability of V/Q scan interpretation in the diagnosis of PE when coupled with SPECT. Unless clinically indicated, the mandate by clinical society guidelines for a normal CXR prior to V/Q should be revisited.

SPECT Ventilation/Perfusion Imaging for Acute Pulmonary Embolism: Meta-analysis of Diagnostic Test Accuracy

RATIONALE AND OBJECTIVES

This study aimed to evaluate the diagnostic accuracies of ventilation/perfusion-single photon emission computed tomography (V/Q-SPECT) imaging modalities for acute pulmonary embolism (PE). These included, in addition to V/Q-SPECT, V/Q-SPECT with low-dose computed tomography (CT; V/Q-SPECT-CT), Q-SPECT with low-dose CT (Q-SPECT-CT), and Q-SPECT.

MATERIALS AND METHODS

PubMed, Embase, CINAHL, and Web of Science databases were searched, and studies included if they studied ≥10 adult participants with acute PE and reported data on the imaging tests' diagnostic performance. Data were meta-analyzed using bivariate random effects regression model.

RESULTS

Data from participants totaling 4146 from 11 V/Q-SPECT studies, 785 from 7 V/Q-SPECT-CT studies, 1196 from 7 Q-SPECT-CT studies, and 728 from five Q-SPECT studies were separately meta-analyzed. The bivariate weighted mean sensitivity and specificity were 0.94 (95% confidence interval [CI]: 0.88-0.97) and 0.95 (95% CI: 0.87-0.98) for V/Q-SPECT, 0.95 (95% CI: 0.88-0.98) and 0.99 (95% CI: 0.92-1.00) for V/Q-SPECT-CT, 0.92 (95% CI: 0.79-0.97) and 0.92 (95% CI: 0.83-0.96) for Q-SPECT-CT, and 0.89 (95% CI: 0.76-0.95) and 0.86 (95% CI: 0.67-0.95) for Q-SPECT studies. The positive and negative likelihood ratios (+LRs and -LRs) were 17.4 (6.9-44.0) and 0.06 (0.03-0.13), 76.7 (11.8-498.0) and 0.06 (0.02-0.13), 11.0 (5.3-22.9) and 0.09 (0.04-0.23), and 6.4 (2.6-15.8) and 0.13 (0.07-0.27) for V/Q-SPECT, V/Q-SPECT-CT, Q-SPECT-CT, and Q-SPECTs, respectively.

CONCLUSION

In the diagnosis of acute PE, this meta-analysis showed that V/Q-SPECT-CT had the highest specificity and +LR. Conversely, Q-SPECT showed the lowest specificity and an unfavorably high -LR.

V/Q SPECT and SPECT/CT in Pulmonary Embolism

Ventilation and perfusion (V/Q) lung scintigraphy has been used in the assessment of patients with suspected pulmonary embolism for more than 50 y. Advances in imaging technology make SPECT and SPECT/CT feasible. This article will examine the application and technical considerations associated with performing 3-dimensional V/Q SPECT and the contribution of a coacquired CT scan. The literature tends to be mixed and contradictory in terms of appropriate investigation algorithms for pulmonary embolism. V/Q SPECT and SPECT/CT offer significant advantages over planar V/Q, with or without the advantages of Technegas ventilation, and if available should be the preferred option in the evaluation of patients with suspected pulmonary embolism.

Diagnosis, Diagnostic Tools, and Risk Stratification for Contemporary Treatment of Pulmonary Embolism

Pulmonary embolism (PE) is quite common and is associated with significant morbidity and mortality. It is estimated that it is the cause of approximately 100,000 annual deaths in the United States. With great variability in presenting symptoms of PE, poor recognition of PE can be fatal. As such, many risk scores have been created to identify the sickest patients. Choosing the appropriate imaging modality is also critical. Invasive pulmonary angiography was once the gold standard to establish the diagnosis. With the advent of nuclear imaging, V/Q scans, invasive angiography has been phased out for diagnosing acute PE. At present, the standard for diagnosis of acute PE is computed tomography pulmonary angiography. In select patient cohorts, nuclear studies remain the modality of choice. Once the diagnosis of acute PE is established, there is a broad spectrum of severity in outcome which has led to substantial focus and development of risk stratification prediction models. We will discuss making the proper diagnosis with contemporary diagnostic tools and risk stratifying patients with PE to receive the correct treatment.

A Technical Overview of Technegas as a Lung Ventilation Agent

Technegas is a carbon-based nanoparticle developed in Australia in 1984 and has been in widespread clinical use, including SPECT imaging, since 1986. Although ^81mKr offers the ideal ventilation properties of a true gas, Technegas is considered preferred in more than 60 countries for ventilation imaging yet has limited adoption in the United States. In March 2020, a new U.S. Food and Drug Administration application was lodged for Technegas, and the impending approval warrants a detailed discussion of the technical aspects of the technology for those for whom it is new. Technegas is a simple yet versatile system for producing high-quality ^99mTc-based ventilation studies. The design affords safety to patients and staff, including consideration of radiation and biologic risks. Technegas is the gold standard for the ventilation portion of SPECT-based ventilation-perfusion studies in pulmonary embolism and several respiratory pathologies. When approved by the U.S. Food and Drug Administration, Technegas will extend advantages to workflow, safety, and study quality for departments that adopt the technology.

Multimodality cardiovascular imaging in pulmonary embolism

Acute pulmonary embolism (APE) is one of the leading causes of cardiovascular (CV) morbidity and mortality. To select appropriate therapeutic strategy and/or to minimize the mortality and morbidity, rapid and correct identification of life-threatening APE is very important. Also, right ventricular (RV) failure usually precedes acute hemodynamic compromise or death, and thus the identification of RV failure is another important step in risk stratification or treatment of APE. With advances in diagnosis and treatment, the prognosis of APE has been dramatically improving in most cases, but inadequate therapy or recurrent episodes of pulmonary embolism (PE) may result in negative outcomes or, so called, chronic thromboembolic pulmonary hypertension (CTEPH). CTEPH is a condition characterized by remaining chronic thromboembolic material in the pulmonary vasculature and subsequent chronic pulmonary hypertension. Various imaging modalities include chest computed tomography pulmonary angiography (CTPA), echocardiography, magnetic resonance imaging, and nuclear imaging and each are used for the assessment of varying status of PE. Assessment of thromboembolic burden by chest CTPA is the first step in the diagnosis of PE. Hemodynamic assessment can be achieved by echocardiography and also by chest CTPA. Nuclear imaging is useful in discriminating CTEPH from APE. Better perspectives on diagnosis, risk stratification and decision making in PE can be provided by combining multimodality CV imaging. Here, the advantages or pitfalls of each imaging modality in diagnosis, risk stratification, or management of PE will be discussed.

A Brief History of Lung Ventilation and Perfusion Imaging Over the 50-Year Tenure of the Editors of Seminars in Nuclear Medicine

The ventilation/perfusion lung scan has been in continuous use for approximately half a century, the same lifetime as Seminars in Nuclear Medicine. Remarkably, the founding Editors-in-Chief have continued to guide the journal over this entire period. In this Feschrift issue celebrating their enormous contribution, we review the history of the lung scan, its highs and lows, the transition from planar to SPECT/CT V/Q scans, and the future that is in store in this age of multimodality functional imaging. We concur with the published view of one of the retiring editors (LMF) that V/Q scintigraphy is indeed alive and well and has a definite future in clinical medicine.

IodiNe Subtraction mapping in the diagnosis of Pulmonary chronIc thRomboEmbolic disease (INSPIRE): Rationale and methodology of a cross-sectional observational diagnostic study

Chronic thromboembolic pulmonary hypertension (CTEPH) is a severe but treatable disease that is commonly underdiagnosed. Computed tomography lung subtraction iodine mapping (CT-LSIM) in addition to standard CT pulmonary angiography (CTPA) may improve the evaluation of suspected chronic pulmonary embolism and improve the diagnostic pick up rate. We aim to recruit 100 patients suspected of having CTEPH and perform CT-LSIM scans in addition to the current gold standard test of nuclear medicine test (lung single photon emission computed tomography (SPECT) imaging) as a pilot study which will contribute to and inform the definitive trial. The diagnostic accuracy of CT-LSIM and lung SPECT will be compared. The primary outcome of the full definitive study is non-inferiority of CT-LSIM versus lung SPECT imaging.

The Economic Value of Hybrid Single-photon Emission Computed Tomography With Computed Tomography Imaging in Pulmonary Embolism Diagnosis

Objective

The objective was to quantify the potential economic value of single‐photon emission computed tomography (SPECT) with computed tomography (CT; SPECT/CT) versus CT pulmonary angiography (CTPA), ventilation–perfusion (V/Q) planar scintigraphy, and V/Q SPECT imaging modalities for diagnosing suspected pulmonary embolism (PE) patients in an emergency setting.

Methods

An Excel‐based simulation model was developed to compare SPECT/CT versus the alternate scanning technologies from a payer's perspective. Clinical endpoints (diagnosis, treatment, complications, and mortality) and their corresponding cost data (2016 USD) were obtained by performing a best evidence review of the published literature. Studies were pooled and parameters were weighted by sample size. Outcomes measured included differences in 1) excess costs, 2) total costs, and 3) lives lost per annum between SPECT/CT and the other imaging modalities. One‐way (±25%) sensitivity and three scenario analyses were performed to gauge the robustness of the results.

Results

For every 1,000 suspected PE patients undergoing imaging, expected annual economic burden by modality was found to be 3.2 million (SPECT/CT), 3.8 million (CTPA), 5.8 million (planar), and 3.6 million (SPECT) USD, with a switch to SPECT/CT technology yielding per‐patient‐per‐month cost savings of $51.80 (vs. CTPA), $213.80 (vs. planar), and $36.30 (vs. SPECT), respectively. The model calculated that the incremental number of lives saved with SPECT/CT was six (vs. CTPA) and three (vs. planar). Utilizing SPECT/CT as the initial imaging modality for workup of acute PE was also expected to save $994,777 (vs. CTPA), $2,852,014 (vs. planar), and $435,038 (vs. SPECT) in “potentially avoidable”’ excess costs per annum for a payer or health plan.

Conclusion

Compared to the currently available scanning technologies for diagnosing suspected PE, SPECT/CT appears to confer superior economic value, primarily via improved sensitivity and specificity and low nondiagnostic rates. In turn, the improved diagnostic accuracy accords this modality the lowest ratio of expenses attributable to potentially avoidable complications, misdiagnosis, and underdiagnosis.

Mosaic attenuation pattern in non-contrast computed tomography for the assessment of pulmonary perfusion in chronic thromboembolic pulmonary hypertension

BACKGROUND

Chronic thromboembolic pulmonary hypertension (CTEPH) is difficult to diagnose as patients rarely present with specific symptoms. However, a mosaic attenuation pattern (MAP) in chest computed tomography (CT) suggests CTEPH. Areas of increased attenuation are not always visible using default CT settings for the lung. Thus, we examined the utility of non-contrast CT imaging with new settings focusing on MAP (CT_Mosaic) for the assessment of pulmonary perfusion in patients with CTEPH. The regional perfusion defects visualized using CT_Mosaic and single-photon-emission CT with fusion of CT images (SPECT/CT) were compared.

METHODS

Twenty-seven patients with CTEPH (20 women; aged 62.8±7.9 years) underwent imaging with non-contrast CT and SPECT/CT. We converted non-contrast mediastinal CT images into various CT window settings to identify the MAP, and the CT window setting that could most easily identify the MAP was defined as CT_Mosaic. We then scored and compared lung segments depending on the degree of perfusion on CT_Mosaic and SPECT/CT.

RESULTS

CT_Mosaic was identified as the CT window setting in which the window level was -800 Hounsfield units (HU), and the window width was 200 HU. Using CT_Mosaic, MAP was detected in 366 of 486 segments (75.3%). The agreement between CT_Mosaic and perfusion defects on SPECT/CT was 84.9%. Weighted kappa statistics demonstrated a good agreement between the two examinations (κ=0.605, 95% confidence interval, 0.502-0.707).

CONCLUSIONS

The CT_Mosaic setting can easily identify an MAP in CTEPH patients. Therefore, this may be useful as a simple and cost-effective evaluation method for blood distribution in patients with CTEPH.

"Pulmonary embolism diagnostics of pregnant patients: What is the recommended clinical pathway considering the clinical value and associated radiation risks of available imaging tests?"

Pulmonary embolism (PE) during pregnancy remains the leading preventable cause of maternal morbidity and mortality in the developed countries. Diagnosis of PE in pregnant patients is a challenging clinical problem, since pregnancy-related physiologic changes can mimic signs and symptoms of PE. Patient mismanagement may result into unjustified anticoagulant treatment or unnecessary imaging tests involving contrast-related or/and radiation-related risks for both the expectant mother and embryo/fetus. On the other hand, missing or delaying diagnosis of PE could lead to life-threatening conditions for both the mother and the embryo/fetus. Thus, a timely and accurate diagnostic approach is required for the optimal management of pregnant patients with suspected PE. Aim of the current review is to discuss a pregnancy-specific clinical pathway for the early diagnosis of PE with non-ionizing radiation- and ionizing radiation-based imaging modalities taking into account previously reported data on diagnostic value of available imaging tests, and radiation related concerns.

Correlation of Ventilation-Perfusion (V/Q) Scan Results as Compared with Clinical Probability of Pulmonary Embolism in African American Population

Introduction Current guidelines suggest the use of the more specific Wells' score could safely reduce the number of unnecessary scans. There is a lack of research to support whether these guidelines apply to the African American population. This study aims to evaluate the correlation of clinical pretest probability of pulmonary embolism (PE) with ventilation-perfusion (V/Q) scan results in a predominantly African American population and to test whether current guidelines based on studies conducted in other populations hold true in this group. Material and Methods A retrospective descriptive study to determine the diagnostic utility of the V/Q scan was conducted among patients who were seen during January 2012 to January 2016. The study population included patients who underwent a V/Q scan for evaluation of PE. One hundred and seventy-five charts were reviewed and 49 were excluded due to poor quality data. A review of the initial history, as well as discharge summaries, was performed. Wells' probability of PE was compared with the results of the scan. Laboratory tests and imaging studies were reviewed and analyzed. Result The median age of the study population was 63.02 ± 16.12 years. The majority of the study population, 121 patients (92.4%), was African American. Sixty-four (48.9%) VQ scans were done for a low clinical probability for pulmonary embolism as defined by the Wells' clinical score. The most common clinical presentations were shortness of breath (SOB) - 74 (58%), leg pain or swelling - 39 (29.8%), chest pain - 36 (27.4%), and syncope - 4 (3.1%). Sixty-two (96.9 %) patients with low clinical probability had low probability VQ scans (P = 0.03). Among the patients who underwent CT angiography and V/Q scanning, a low probability scan was noted in 25 patients with no pulmonary embolism on CT (96.2 %) (P = 0.006). Conclusions This study showed a strong correlation between low clinical probability and low probability V/Q scans and its utility to safely rule out PE in a predominantly black population. Studies conducted in other populations have detected similar findings.

(68)Ga PET Ventilation and Perfusion Lung Imaging-Current Status and Future Challenges

Gallium-68 ((68)Ga) is a positron-emitting radionuclide suitable for positron emission tomography (PET) imaging that has a number of convenient features-it has a physical half life of 68 minutes, it is generator produced at the PET facility and needs no local cyclotron, and being a radiometal is able to be chelated to a number of useful molecules for diagnostic imaging with PET. (68)Ga has recently been investigated as a radiotracer for ventilation and perfusion (V/Q) lung imaging. It is relatively easy to produce both V/Q radiopharmaceuticals labeled with (68)Ga for PET studies, it offers higher spatial resolution than equivalent SPECT studies, the short half life allows for multiple (repeated) scans on the same day, and low amounts of radiotracer can be used thus limiting the radiation dose to the subject. In the usual clinical setting requiring a V/Q scan, that of suspected pulmonary embolism, the role of (68)Ga V/Q PET may be limited from a logistical perspective, however, in nonacute applications such as lung function evaluation, radiotherapy treatment planning, and respiratory physiology investigations it would appear to be an ideal modality to employ.

[MRI methods for pulmonary ventilation and perfusion imaging]

CLINICAL/METHODICAL ISSUE

Separate assessment of respiratory mechanics, gas exchange and pulmonary circulation is essential for the diagnosis and therapy of pulmonary diseases. Due to the global character of the information obtained clinical lung function tests are often not sufficiently specific in the differential diagnosis or have a limited sensitivity in the detection of early pathological changes.

STANDARD RADIOLOGICAL METHODS

The standard procedures of pulmonary imaging are computed tomography (CT) for depiction of the morphology as well as perfusion/ventilation scintigraphy and single photon emission computed tomography (SPECT) for functional assessment.

METHODICAL INNOVATIONS

Magnetic resonance imaging (MRI) with hyperpolarized gases, O2-enhanced MRI, MRI with fluorinated gases and Fourier decomposition MRI (FD-MRI) are available for assessment of pulmonary ventilation. For assessment of pulmonary perfusion dynamic contrast-enhanced MRI (DCE-MRI), arterial spin labeling (ASL) and FD-MRI can be used.

PERFORMANCE

Imaging provides a more precise insight into the pathophysiology of pulmonary function on a regional level. The advantages of MRI are a lack of ionizing radiation, which allows a protective acquisition of dynamic data as well as the high number of available contrasts and therefore accessible lung function parameters.

ACHIEVEMENTS

Sufficient clinical data exist only for certain applications of DCE-MRI. For the other techniques, only feasibility studies and case series of different sizes are available. The clinical applicability of hyperpolarized gases is limited for technical reasons.

PRACTICAL RECOMMENDATIONS

The clinical application of the techniques described, except for DCE-MRI, should be restricted to scientific studies.

Pulmonary ventilation/perfusion single photon emission tomography--Initial experience of a Nuclear Medicine Department

INTRODUCTION

Lung ventilation/perfusion scintigraphy with planar images (V/QS-planar) is very useful for the diagnosis and follow-up of pulmonary thromboembolism (PTE). Acquiring tomographic images (V/QS-SPECT) is a recent development with potential to increase the technique's accuracy. The purpose of this work is to evaluate the added benefits of V/QS-SPECT studies as opposed to traditional planar imaging.

PATIENTS AND METHODS

We prospectively revised 53 V/QS-planar and V/QS-SPECT exams, performed according to the European Association of Nuclear Medicine guidelines. We evaluated the exams independently, by consensus of two Nuclear Medicine physicians. For both methods, we gave each lung a score expressing the dimension and extension of perfusion defects with normal ventilation. For each lung, we compared the scores with the paired Wilcoxon test, estimating the 95% confidence interval (95 CI) for the respective difference.

RESULTS

We performed V/QS-SPECT exams without technical difficulties. The paired Wilcoxon test estimated the score difference to be -0.75 (95 CI of -1.0 to -0.5; p-value=9.6 × 10(-7)), expressing a statistically significant difference of about 1 subsegmental defect between both methods, with V/QS-SPECT detecting more defects.

DISCUSSION

The results demonstrate that V/QS-SPECT identifies a slightly larger number of perfusion defects than V/QS-planar, suggesting a higher sensitivity of this technique. However, more studies are necessary to evaluate the clinical meaning of this fact.

CONCLUSION

V/QS-SPECT demonstrates a higher capability to identify perfusion defects. This method looks promising, allowing for a greater role of this exam in pulmonary thromboembolism diagnosis and follow-up.

Ventilation/perfusion SPECT/CT in patients with pulmonary emphysema. Evaluation of software-based analysing

The purpose of this study was to evaluate the reproducibility of a new software based analysing system for ventilation/perfusion single-photon emission computed tomography/computed tomography (V/P SPECT/CT) in patients with pulmonary emphysema and to compare it to the visual interpretation.

PATIENTS, MATERIAL AND METHODS

19 patients (mean age: 68.1 years) with pulmonary emphysema who underwent V/P SPECT/CT were included. Data were analysed by two independent observers in visual interpretation (VI) and by software based analysis system (SBAS). SBAS PMOD version 3.4 (Technologies Ltd, Zurich, Switzerland) was used to assess counts and volume per lung lobe/per lung and to calculate the count density per lung, lobe ratio of counts and ratio of count density. VI was performed using a visual scale to assess the mean counts per lung lobe. Interobserver variability and association for SBAS and VI were analysed using Spearman's rho correlation coefficient.

RESULTS

Interobserver agreement correlated highly in perfusion (rho: 0.982, 0.957, 0.90, 0.979) and ventilation (rho: 0.972, 0.924, 0.941, 0.936) for count/count density per lobe and ratio of counts/count density in SBAS. Interobserver agreement correlated clearly for perfusion (rho: 0.655) and weakly for ventilation (rho: 0.458) in VI.

CONCLUSIONS

SBAS provides more reproducible measures than VI for the relative tracer uptake in V/P SPECT/CTs in patients with pulmonary emphysema. However, SBAS has to be improved for routine clinical use.

The accuracy of V/Q SPECT in the diagnosis of pulmonary embolism: a meta-analysis

BACKGROUND

Ventilation perfusion single photon emission computed tomography (V/Q SPECT) and CT pulmonary angiography have all been used in the diagnosis of acute PE. Previous studies have shown higher sensitivity and specificity and a marked decrease in the non-diagnostic rate of V/Q SPECT than planar scan.

PURPOSE

To systematically review and perform a meta-analysis of published data on the performance of V/Q SPECT in the diagnosis of acute PE.

MATERIAL AND METHODS

A comprehensive computer search was conducted on literature published through 31 December 2013 in an effort to find relevant articles on the diagnostic performance of V/Q SPECT in the diagnosis of PE patients. Pooled sensitivity, specificity, negative likelihood ratio (LR), and positive LR, the area under the receiver-operating characteristic (ROC) curve of V/Q SPECT in the diagnosis of PE patients were calculated.

RESULTS

Nine studies, comprising a total sample size of 3454 patients, were included in our meta-analysis. The pooled sensitivity, specificity of V/Q SPECT in the diagnosis of acute PE patients, calculated on a per-patient-based analysis, was 96% (95% confidence interval [CI], 95-97%), 97% (95% CI, 96-98%). The pooled negative LR, positive LR of V/Q SPECT in acute PE patients was 0.06 (range, 0.02-0.19) and 16.64 (range, 9.78-31.54). The area under the ROC curve of V/Q SPECT in the diagnosis of acute PE patients was 0.99 on a per-patient-based analysis.

CONCLUSION

V/Q SPECT is an accurate method in acute PE patients with high sensitivity and high specificity in the diagnosis of PE.

Three-dimensional pulmonary perfusion MRI with radial ultrashort echo time and spatial-temporal constrained reconstruction

PURPOSE

To assess the feasibility of spatial-temporal constrained reconstruction for accelerated regional lung perfusion using highly undersampled dynamic contrast-enhanced (DCE) three-dimensional (3D) radial MRI with ultrashort echo time (UTE).

METHODS

A combined strategy was used to accelerate DCE MRI for 3D pulmonary perfusion with whole lung coverage. A highly undersampled 3D radial UTE MRI acquisition was combined with an iterative constrained reconstruction exploiting principal component analysis and wavelet soft-thresholding for dimensionality reduction in space and time. The performance of the method was evaluated using a 3D fractal-based DCE digital lung phantom. Simulated perfusion maps and contrast enhancement curves were compared with ground truth using the structural similarity index (SSIM) to determine robust threshold and regularization levels. Feasibility studies were then performed in a canine and a human subject with 3D radial UTE (TE=0.08 ms) acquisition to assess feasibility of mapping regional 3D perfusion.

RESULTS

The method was able to accurately recover perfusion maps in the phantom with a nominal isotropic spatial resolution of 1.5 mm (SSIM of 0.949). The canine and human subject studies demonstrated feasibility for providing artifact-free perfusion maps in a simple 3D breath-held acquisition.

CONCLUSION

The proposed method is promising for fast and flexible 3D pulmonary perfusion imaging. Magn Reson

A prospective observational study of Gallium-68 ventilation and perfusion PET/CT during and after radiotherapy in patients with non-small cell lung cancer

Background

Non-small cell lung cancer (NSCLC) accounts for 85% of lung cancers, and is the leading cause of cancer deaths. Radiation therapy (RT), alone or in combination with chemotherapy, is the standard of care for curative intent treatment of patients with locally advanced or inoperable NSCLC. The ability to intensify treatment to achieve a better chance for cure is limited by the risk of injury to the surrounding lung.

Methods/Design

This is a prospective observational study of 60 patients with NSCLC receiving curative intent RT. Independent human ethics board approval was received from the Peter MacCallum Cancer Centre ethics committee. In this research, Galligas and Gallium-68 macroaggregated albumin (MAA) positron emission tomography (PET) imaging will be used to measure ventilation (V) and perfusion (Q) in the lungs. This is combined with computed tomography (CT) and both performed with a four dimensional (4D) technique that tracks respiratory motion. This state-of-the-art scan has superior resolution, accuracy and quantitative ability than previous techniques. The primary objective of this research is to observe changes in ventilation and perfusion secondary to RT as measured by 4D V/Q PET/CT. Additionally, we plan to model personalised RT plans based on an individual’s lung capacity. Increasing radiation delivery through areas of poorly functioning lung may enable delivery of larger, more effective doses to tumours without increasing toxicity. By performing a second 4D V/Q PET/CT scan during treatment, we plan to simulate biologically adapted RT depending on the individual’s accumulated radiation injury. Tertiary aims of the study are assess the prognostic significance of a novel combination of clinical, imaging and serum biomarkers in predicting for the risk of lung toxicity. These biomarkers include spirometry, 18 F-Fluorodeoxyglucose PET/CT, gamma-H2AX signals in hair and lymphocytes, as well as assessment of blood cytokines.

Discussion

By correlating these biomarkers to toxicity outcomes, we aim to identify those patients early who will not tolerate RT intensification during treatment. This research is an essential step leading towards the design of future biologically adapted radiotherapy strategies to mitigate the risk of lung injury during dose escalation for patients with locally advanced lung cancer.

Trials registration

Universal Trial Number (UTN) U1111-1138-4421.

Noncontrast perfusion single-photon emission CT/CT scanning: a new test for the expedited, high-accuracy diagnosis of acute pulmonary embolism

BACKGROUND

Standard ventilation and perfusion (V˙/Q˙) scintigraphy uses planar images for the diagnosis of pulmonary embolism (PE). To evaluate whether tomographic imaging improves the diagnostic accuracy of the procedure, we compared noncontrast perfusion single-photon emission CT (Q˙-SPECT)/CT scans with planar V˙/Q˙scans in patients at high risk for PE.

METHODS

Between 2006 and 2010, most patients referred for diagnosis of PE underwent both Q˙-SPECT/CT scan and planar V˙/Q˙scintigraphy. All scans were reviewed retrospectively by four observers; planar scans were read with modified Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) II and Prospective Investigative Study of Pulmonary Embolism Diagnosis (PISA-PED) criteria. On Q˙-SPECT/CT scan, any wedge-shaped peripheral perfusion defect occupying > 50% of a segment without corresponding pulmonary parenchymal or pleural disease was considered to show PE. The final diagnosis was established with a composite reference standard that included ECG, ultrasound of lower-extremity veins, D-dimer levels, CT pulmonary angiography (when available), and clinical follow-up for at least 3 months.

RESULTS

One hundred six patients with cancer and mean Wells score of 4.4 had sufficient follow-up; 22 patients were given a final diagnosis of PE, and 84 patients were given a final diagnosis of no PE. According to PIOPED II, 13 studies were graded as intermediate probability. Sensitivity and specificity for PE were 50% and 98%, respectively, based on PIOPED II criteria; 86% and 93%, respectively, based on PISA-PED criteria; and 91% and 94%, respectively, based on Q˙-SPECT/CT scan. Seventy-six patients had additional relevant findings on the CT image of the Q˙-SPECT/CT scan.

CONCLUSIONS

Noncontrast Q˙-SPECT/CT imaging has a higher accuracy than planar V˙/Q˙imaging based on PIOPED II criteria in patients with cancer and a high risk for PE.

Thirty years from now: future physics contributions in nuclear medicine

Background

This paper is the first in a series of invited perspectives by pioneers of nuclear medicine imaging and physics. A medical physicist and a nuclear medicine physician each take a backward and a forward look at the contributions of physics to nuclear medicine. Here, we provide a forward look from the medical physicist’s perspective.

Discussion

The author examines a number of developments in nuclear medicine and discusses the ways in which physics has contributed to these. Future developments are postulated in the context of an increasingly personalised approach to medical diagnostics and therapies.

Conclusions

A skill set for the next generation of medical physicists in nuclear medicine is proposed in the context of the increasing complexity of ‘Molecular Imaging’ in the next three decades. The author sees a shift away from ‘traditional’ roles in instrumentation QA to more innovative approaches in understanding radiobiology and human disease.

Impact of inflammation, emphysema, and smoking cessation on V/Q in mouse models of lung obstruction

Background

Chronic obstructive pulmonary disease (COPD) is known to greatly affect ventilation (V) and perfusion (Q) of the lung through pathologies such as inflammation and emphysema. However, there is little direct evidence regarding how these pathologies contribute to the V/Q mismatch observed in COPD and models thereof. Also, little is known regarding how smoking cessation affects V/Q relationships after inflammation and airspace enlargement have become established. To this end, we have quantified V/Q on a per-voxel basis using single photon emission computed tomography (SPECT) in mouse models of COPD and lung obstruction.

Methods

Three distinct murine models were used to investigate the impact of different pathologies on V/Q, as measured by SPECT. Lipopolysaccharide (LPS) was used to produce neutrophilic inflammation, porcine pancreatic elastase (PPE) was used to produce emphysema, and long-term cigarette smoke (CS) exposure and cessation were used to investigate the combination of these pathologies.

Results

CS exposure resulted in an increase in mononuclear cells and neutrophils, an increase in airspace enlargement, and an increase in V/Q mismatching. The inflammation produced by LPS was more robust and predominantly neutrophilic, compared to that of cigarette smoke; nevertheless, inflammation alone caused V/Q mismatching similar to that seen with long-term CS exposure. The emphysematous lesions caused by PPE administration were also capable of causing V/Q mismatch in the absence of inflammation. Following CS cessation, inflammatory cell levels returned to those of controls and, similarly, V/Q measures returned to normal despite evidence of persistent mild airspace enlargement.

Conclusions

Both robust inflammation and extensive airspace enlargement, on their own, were capable of producing V/Q mismatch. As CS cessation resulted in a return of V/Q mismatching and inflammatory cell counts to control levels, lung inflammation is likely a major contributor to V/Q mismatch observed in the cigarette smoke exposure model as well as in COPD patients. This return of V/Q mismatching to control values also took place in the presence of mild airspace enlargement, indicating that emphysematous lesions must be of a larger volume before affecting the lung significantly. Early smoking cessation is therefore critical before emphysema has an irreversible impact on gas exchange.

Contribution of V/Q SPECT to planar scintigraphy in the diagnosis of pulmonary embolism

AIM

To evaluate the feasibility of V/Q SPECT and analyze its contribution to planar V/Q lung scintigraphy in the diagnosis of pulmonary embolism (PE).

MATERIAL AND METHODS

A total of 109 patients with suspected PE showing Wells score>2 and elevated D-dimer were studied. The V/Q could not be completed in 7 patients, so they were excluded. Ventilation and perfusion scans were done using Technegas and (99m)Tc-MAA. Planar study included 8 projections on a 256×256 matrix and 128 projections on a 128×128 matrix were acquired for the SPECT study, applying an iterative method. Planar images were interpreted according to modified PIOPED criteria, and SPECT by the guidelines of the EANMMI. The results with both techniques were compared.

RESULTS

V/Q planar scintigraphy and SPECT could be performed in 102 patients. V/Q planar scintigraphy was considered "diagnostic" in 39 of the 102 patients, and "non-diagnostic" in 63. Of the 39 "diagnostic" studies, 31 were reported as high probability of PE and 8 as normal. Of the 63 "non-diagnostic", 26 corresponded to intermediate, 29 to low, and 8 to very low probability. The SPECT study was "diagnostic" in 97 and indeterminate in only 5. All patients with a high probability planar scintigraphy had a positive SPECT. In the 8 patients with a normal planar scintigraphy SPECT was negative in 5 and positive in 3. In the 63 patients with a "non-diagnostic" planar scintigraphy SPECT was "diagnostic" in 58 of them, positive in 17 and negative in 41.

CONCLUSION

V/Q SPECT is a feasible technique as it was performed in 102 of the 109 patients who were enrolled in the study (94%). The addition of V/Q SPECT to planar V/Q decreases the number of "non-diagnostic" reports from 62% in planar scintigraphy to 4.9% in SPECT. Therefore, V/Q SPECT should be included in the diagnosis approach of PE due to its high diagnostic yield.

Improved visualization of perfusion defects by respiratory-gated SPECT: a phantom simulation study

OBJECTIVES

Single-photon emission computed tomography ventilation/perfusion (SPECT V/Q) imaging is recommended both by the Society of Nuclear Medicine and by the European Association of Nuclear Medicine for the diagnosis of pulmonary embolism. However, respiratory motion produces image blurring and degradation of detail in the lungs. We have investigated respiratory gating of SPECT images, correcting for motion to reduce blur and improve image definition.

MATERIALS AND METHODS

Wedge-shaped defects of different sizes ranging from 15 to 4 mm were fixed in the lung cavities of an anthropomorphic lung phantom to simulate perfusion defects. Gated and nongated SPECT images were obtained using a double-headed SPECT system. Three-dimensional movement was introduced using a purpose-built moving platform with two motion frequencies of 10 and 20 cycles/min. Motion was tracked with a respiratory-gating system. Gated SPECT data were acquired in 16 discrete data bins in synchronization with the breathing cycle. The images were reconstructed using ordered-subset expectation maximization algorithms and corrected for rigid motion. Contrast and contrast-to-noise ratios (CNRs) were measured to quantify any improvement in the gated motion-corrected images. Visualization of defects in the reconstructed images was performed by seven observers and analyzed using alternative free-response receiver operating characteristic analysis.

RESULTS

Assessment of gated and nongated SPECT phantom images demonstrated that motion adversely affected the detectability of defects. Quantification of data demonstrated that, in the controlled simulation, image quality, defect definition, observer confidence, contrast, and CNR were increased after applying motion correction. Improvement in CNRs was found to be significant using alternative free-response receiver operating characteristic analysis (P=0.0002).

CONCLUSION

Respiratory-gated motion-corrected SPECT images enhanced the visualization of defects compared with matched moving/nongated images in a realistic moving phantom. This approach may be particularly valuable for SPECT V/Q imaging and may improve the diagnosis of pulmonary embolism.

SPECT/CT and pulmonary embolism

Acute pulmonary embolism (PE) is diagnosed either by ventilation/perfusion (V/P) scintigraphy or pulmonary CT angiography (CTPA). In recent years both techniques have improved. Many nuclear medicine centres have adopted the single photon emission CT (SPECT) technique as opposed to the planar technique for diagnosing PE. SPECT has been shown to have fewer indeterminate results and a higher diagnostic value. The latest improvement is the combination of a low-dose CT scan with a V/P SPECT scan in a hybrid tomograph. In a study comparing CTPA, planar scintigraphy and SPECT alone, SPECT/CT had the best diagnostic accuracy for PE. In addition, recent developments in the CTPA technique have made it possible to image the pulmonary arteries of the lungs in one breath-hold. This development is based on the change from a single-detector to multidetector CT technology with an increase in volume coverage per rotation and faster rotation. Furthermore, the dual energy CT technique is a promising modality that can provide functional imaging in combination with anatomical information. Newer high-end CT scanners and SPECT systems are able to visualize smaller subsegmental emboli. However, consensus is lacking regarding the clinical impact and treatment. In the present review, SPECT and SPECT in combination with low-dose CT, CTPA and dual energy CT are discussed in the context of diagnosing PE.

Non-contrast-enhanced preoperative assessment of lung perfusion in patients with non-small-cell lung cancer using Fourier decomposition magnetic resonance imaging

OBJECTIVE

To investigate non-contrast-enhanced Fourier decomposition MRI (FD MRI) for assessment of regional lung perfusion in patients with Non-Small-Cell Lung Cancer (NSCLC) in comparison to dynamic contrast-enhanced MRI (DCE MRI).

METHODS

Time-resolved non-contrast-enhanced images of the lungs were acquired prospectively in 15 patients using a 2D balanced steady-state free precession (b-SSFP) sequence. After non-rigid registration of the native image data, perfusion-weighted images were calculated by separating periodic changes of lung proton density at the cardiac frequency using FD. DCE MRI subtraction datasets were acquired as standard of reference. Both datasets were analyzed visually for perfusion defects. Then segmentation analyses were performed to describe perfusion of pulmonary lobes semi-quantitatively as percentages of total lung perfusion. Overall FD MRI perfusion signal was compared to velocity-encoded flow measurements in the pulmonary trunk as an additional fully quantitative reference.

RESULTS

Image quality ratings of FD MRI were significantly inferior to those of DCE MRI (P<0.0001). Sensitivity, specificity, and accuracy of FD MRI for visual detection of perfusion defects were 84%, 92%, and 91%. Semi-quantitative evaluation of lobar perfusion provided high agreement between FD MRI and DCE MRI for both entire lungs and upper lobes, but less agreement in the lower parts of both lungs. FD perfusion signal showed high linear correlation with pulmonary arterial blood flow.

CONCLUSION

FD MRI is a promising technique that allows for assessing regional lung perfusion in NSCLC patients without contrast media or ionizing radiation. However, for being applied in clinical routine, image quality and robustness of the technique need to be further improved.

V/Q scanning using SPECT and SPECT/CT

Planar ventilation-perfusion (V/Q) scanning is often used to investigate pulmonary embolism; however, it has well-recognized limitations. SPECT overcomes many of these through its ability to generate 3-dimensional imaging data. V/Q SPECT has higher sensitivity, specificity, and accuracy than planar imaging and a lower indeterminate rate. SPECT allows for new ways to display and analyze data, such as parametric V/Q ratio images. Compared with CT pulmonary angiography, SPECT has higher sensitivity, a lower radiation dose, fewer technically suboptimal studies, and no contrast-related complications. Any nuclear medicine department equipped with a modern hybrid scanner can now perform combined V/Q SPECT with CT (using low-dose protocols) to further enhance diagnostic accuracy. V/Q SPECT (with or without CT) has application in other pulmonary conditions and in research.

Detection of lung dysfunction using ventilation and perfusion SPECT in a mouse model of chronic cigarette smoke exposure

Chronic obstructive pulmonary disease is a leading cause of morbidity and mortality worldwide. Exposure to cigarette smoke (CS) is a major risk factor for developing this chronic airflow impairment, but the early progression of disease is not well defined or understood. Ventilation/perfusion (V/Q) SPECT provides a noninvasive assessment of lung function to further our current understanding of how CS affects the lung.

METHODS

BALB/c mice were imaged with V/Q SPECT and CT after 8 and 24 wk of whole-body exposure to mainstream CS. Bronchoalveolar lavage was collected and cell differentials produced to determine inflammatory patterns. Histologic lung sections were collected, and a semiautomated quantitative analysis of airspace enlargement was applied to whole histology slices.

RESULTS

Exposure to CS induced an inflammatory response that included increases in the numbers of both mononuclear cells and neutrophils. Airspace enlargement was also significantly increased at 8 wk of CS exposure and was still more pronounced at 24 wk. Ventilation and perfusion correlation at the voxel level depicted a significant decrease in matching at 8 wk of CS exposure that was also apparent after 24 wk. The standard deviation (SD) of the log(V/Q) curve, a basic measure of heterogeneity, was increased from 0.44 ± 0.02 in age-matched controls to 0.62 ± 0.05 with CS exposure at 24 wk, indicating an increase in V/Q mismatching between 8 and 24 wk of CS exposure. CT, however, was not capable of discriminating control from CS-exposed animals at either time point, even with greater resolution and respiratory gating.

CONCLUSION

This study demonstrated that, before CT detection of structural changes, V/Q imaging detected changes in gas-exchange potential. This functional impairment corresponded to increased lung inflammation and increased airspace enlargement. In vivo V/Q imaging can detect early changes to the lung caused by CS exposure and thus provides a noninvasive method of longitudinally studying lung dysfunction in preclinical models. In the future, these measures could be applied clinically to study and diagnose the early stages of chronic obstructive pulmonary disease.

Ventilation and perfusion magnetic resonance imaging of the lung

A close interaction between the respiratory pump, pulmonary parenchyma and blood circulation is essential for a normal lung function. Many pulmonary diseases present, especially in their initial phase, a variable regional impairment of ventilation and perfusion. In the last decades various techniques have been established to measure the lung function. Besides the global pulmonary function tests (PFTs) imaging techniques gained increasing importance to detect local variations in lung function, especially for ventilation and perfusion assessment. Imaging modalities allow for a deeper regional insight into pathophysiological processes and enable improved planning of invasive procedures. In contrast to computed tomography (CT) and the nuclear medicine techniques, magnetic resonance imaging (MRI), as a radiation free imaging modality gained increasing importance since the early 1990 for the assessment of pulmonary function. The major inherent problems of lung tissue, namely the low proton density and the pulmonary and cardiac motion, were overcome in the last years by a constant progress in MR technology. Some MR techniques are still under development, a process which is driven by scientific questions regarding the physiology and pathophysiology of pulmonary diseases, as well as by the need for fast and robust clinically applicable imaging techniques as safe therapy monitoring tools. MRI can be considered a promising ionizing-free alternative to techniques like CT or nuclear medicine techniques for the evaluation of lung function. The goal of this article is to provide an overview on selected MRI techniques for the assessment of pulmonary ventilation and perfusion.

A three dimensional drive system for use with fillable emission phantoms for SPECT and PET imaging

Respiratory motion artefacts pose significant challenges for imaging of the lung and thorax. Dynamic phantoms have previously been applied to the study of respiratory motion, however, most moving platforms have been capable of movement in either one or two dimensions only. We describe a moving platform suitable for SPECT-CT and PET-CT imaging. The platform allows a fillable emission phantom to simulate rigid motion in three dimensions. Elliptical periodical motion of 1.5 cm in all three orthogonal planes was simulated using a series of cams moving a baseplate up and across a slope of 45°. The frequency of movement can be varied manually between 5 and 25 cycles per minute in a known calibrated and reproducible manner (This encompasses the range of physiological respiratory motion). Preliminary studies demonstrated that the phantom can be used to identify motion parameters and for the qualitative assessment of motion blurring in reconstructed images.

Lung ventilation- and perfusion-weighted Fourier decomposition magnetic resonance imaging: in vivo validation with hyperpolarized 3He and dynamic contrast-enhanced MRI

The purpose of this work was to validate ventilation-weighted (VW) and perfusion-weighted (QW) Fourier decomposition (FD) magnetic resonance imaging (MRI) with hyperpolarized (3)He MRI and dynamic contrast-enhanced perfusion (DCE) MRI in a controlled animal experiment. Three healthy pigs were studied on 1.5-T MR scanner. For FD MRI, the VW and QW images were obtained by postprocessing of time-resolved lung image sets. DCE acquisitions were performed immediately after contrast agent injection. (3)He MRI data were acquired following the administration of hyperpolarized helium and nitrogen mixture. After baseline MR scans, pulmonary embolism was artificially produced. FD MRI and DCE MRI perfusion measurements were repeated. Subsequently, atelectasis and air trapping were induced, which followed with FD MRI and (3)He MRI ventilation measurements. Distributions of signal intensities in healthy and pathologic lung tissue were compared by statistical analysis. Images acquired using FD, (3)He, and DCE MRI in all animals before the interventional procedure showed homogeneous ventilation and perfusion. Functional defects were detected by all MRI techniques at identical anatomical locations. Signal intensity in VW and QW images was significantly lower in pathological than in healthy lung parenchyma. The study has shown usefulness of FD MRI as an alternative, noninvasive, and easily implementable technique for the assessment of acute changes in lung function.

Pulmonary functional imaging: qualitative comparison of Fourier decomposition MR imaging with SPECT/CT in porcine lung

PURPOSE

To compare unenhanced lung ventilation-weighted (VW) and perfusion-weighted (QW) imaging based on Fourier decomposition (FD) magnetic resonance (MR) imaging with the clinical reference standard single photon emission computed tomography (SPECT)/computed tomography (CT) in an animal experiment.

MATERIALS AND METHODS

The study was approved by the local animal care committee. Lung ventilation and perfusion was assessed in seven anesthetized pigs by using a 1.5-T MR imager and SPECT/CT. For time-resolved FD MR imaging, sets of lung images were acquired by using an untriggered two-dimensional balanced steady-state free precession sequence (repetition time, 1.9 msec; echo time, 0.8 msec; acquisition time per image, 118 msec; acquisition rate, 3.33 images per second; flip angle, 75°; section thickness, 12 mm; matrix, 128 × 128). Breathing displacement was corrected with nonrigid image registration. Parenchymal signal intensity was analyzed pixelwise with FD to separate periodic changes of proton density induced by respiration and periodic changes of blood flow. Spectral lines representing respiratory and cardiac frequencies were integrated to calculate VW and QW images. Ventilation and perfusion SPECT was performed after inhalation of dispersed technetium 99m ((99m)Tc) and injection of (99m)Tc-labeled macroaggregated albumin. FD MR imaging and SPECT data were independently analyzed by two physicians in consensus. A regional statistical analysis of homogeneity and pathologic signal changes was performed.

RESULTS

Images acquired in healthy animals by using FD MR imaging and SPECT showed a homogeneous distribution of VW and QW imaging and pulmonary ventilation and perfusion, respectively. The gravitation-dependent signal distribution of ventilation and perfusion in all animals was similarly observed at FD MR imaging and SPECT. Incidental ventilation and perfusion defects were identically visualized by using both modalities.

CONCLUSION

This animal experiment demonstrated qualitative agreement in the assessment of regional lung ventilation and perfusion between contrast media-free and radiation-free FD MR imaging and conventional SPECT/CT.

Imaging techniques and the evaluation of the right heart and the pulmonary circulation

Since the right side of the heart and the pulmonary circulation are regarded as secondary components of the circulatory system, their role in disease has traditionally not received the same attention as their counterparts in the systemic circulation. This was partly because precise noninvasive study of these structures was difficult. For many years, chest radiography and invasive angiography were the only techniques available for imaging the minor circulation. The development of transthoracic echocardiography and nuclear techniques has produced a significant leap forward for noninvasive imaging, particularly of the right ventricle. More recently, novel echocardiographic techniques, and advances in computed tomography and magnetic resonance imaging, in particular, have expanded our diagnostic armamentarium and provided new insights into the anatomy and function of the pulmonary circulation in both health and disease. This article contains a review of the current status of techniques for imaging the right side of the heart and the pulmonary circulation.