Effect of inspiratory and expiratory breathhold on pulmonary perfusion: assessment by pulmonary perfusion magnetic resonance imaging

RATIONALE AND OBJECTIVES: The effect of breathholding on pulmonary perfusion remains largely unknown. The aim of this study was to assess the effect of inspiratory and expiratory breathhold on pulmonary perfusion using quantitative pulmonary perfusion magnetic resonance imaging (MRI). METHODS AND RESULTS: Nine healthy volunteers (median age, 28 years; range, 20-45 years) were examined with contrast-enhanced time-resolved 3-dimensional pulmonary perfusion MRI (FLASH 3D, TR/TE: 1.9/0.8 ms; flip angle: 40 degrees; GRAPPA) during end-inspiratory and expiratory breathholds. The perfusion parameters pulmonary blood flow (PBF), pulmonary blood volume (PBV), and mean transit time (MTT) were calculated using the indicator dilution theory. As a reference method, end-inspiratory and expiratory phase-contrast (PC) MRI of the pulmonary arterial blood flow (PABF) was performed. RESULTS: There was a statistically significant increase of the PBF (delta = 182 mL/100 mL/min), PBV (delta = 12 mL/100 mL), and PABF (delta = 0.5 L/min) between inspiratory and expiratory breathhold measurements (P < 0.0001). Also, the MTT was significantly shorter (delta = -0.5 sec) at expiratory breathhold (P = 0.03). Inspiratory PBF and PBV showed a moderate correlation (r = 0.72 and 0.61, P < or = 0.008) with inspiratory PABF. CONCLUSION: Pulmonary perfusion during breathhold depends on the inspiratory level. Higher perfusion is observed at expiratory breathhold.     

Quantitative assessment of regional pulmonary perfusion in the entire lung using three-dimensional ultrafast dynamic contrast-enhanced magnetic resonance imaging: Preliminary experience in 40 subjects

PURPOSE: To assess regional differences in quantitative pulmonary perfusion parameters, i.e., pulmonary blood flow (PBF), mean transit time (MTT), and pulmonary blood volume (PBV) in the entire lung on a pixel-by-pixel basis in normal volunteers and pulmonary hypertension patients. MATERIALS AND METHODS: Three-dimensional ultrafast dynamic contrast-enhanced MR imaging was performed in 15 normal volunteers and 25 patients with pulmonary hypertension. From the signal intensity-time course curves, PBF, MTT and PBV maps were generated using deconvolution analysis, indicator dilution theories, and the central volume principle, on a pixel-by-pixel basis. From pulmonary perfusion parameter maps of normal volunteers and pulmonary hypertension patients, regional PBF, MTT, and PBV were statistically evaluated. RESULTS: Regional PBF, MTT, and PBV showed significant differences in the gravitational and isogravitational directions (P < 0.05). The quantitative pulmonary perfusion parameter maps demonstrated significant differences between normal volunteers and pulmonary hypertension patients (P < 0.05). CONCLUSION: Three-dimensional ultrafast dynamic contrast-enhanced MR imaging is feasible for the assessment of regional quantitative pulmonary perfusion parameters in the entire lung on a pixel-by-pixel basis in normal volunteers and pulmonary hypertension patients.     

Dual-energy CT evidence of pulmonary microvascular occlusion in patients with sickle cell disease experiencing acute chest syndrome

PurposeAcute chest syndrome (ACS), defined by the presence of a chest radiographic opacity in sickle cell disease patients experiencing respiratory symptoms is a leading cause of death in these patients. The etiology is ACS is not well understood however pulmonary microvascular occlusion has been postulated to be a major pathophysiologic driver. Our study aims to assess the value of dual-energy CT (DECT) as a marker of pulmonary microvascular occlusion.Materials/methodsA search tool was used to identify CT angiography studies from 1/1/2017 to 9/15/2019 with any variation of the phrases “Acute chest syndrome” and “Sickle cell”. These studies were manually reviewed for the use of DECT technique. An age-matched control group was created. DECT pulmonary blood volume (PBV) maps were reviewed semi-quantitatively for the presence of iodine defects and the number of involved bronchopulmonary segments were scored. Other recorded values included type of parenchymal opacities, diameter of main pulmonary artery (MPA) and presence of right ventricular dilatation. Mean values between cases and controls were compared using a two-sample t-test.ResultsNine sickle cell DECT cases with PBV maps and nine age-matched controls were evaluated. Bronchopulmonary segments with iodine defects were significantly higher in cases vs controls (mean: 4.7 vs 0.3, p < 0.003). PBV defects were more extensive than parenchymal findings. MPA diameter was higher in cases (2.9 cm) vs control (2.4 cm), P < 0.03.ConclusionsDECT demonstrates abnormal PBV in sickle cell patients, often the predominant abnormality identified early, and likely reflects the presence of pulmonary microvascular occlusion.     

Quantitative 3D pulmonary MR-perfusion in patients with pulmonary arterial hypertension: correlation with invasive pressure measurements

PURPOSE: Pathological changes of the peripheral pulmonary arteries induce pulmonary arterial hypertension (PAH). Aim of this study was to quantitatively assess the effect of PAH on pulmonary perfusion by 3D-MR-perfusion techniques and to compare findings to healthy controls. Furthermore, quantitative perfusion data were correlated with invasive pressure measurements. MATERIAL AND METHODS: Five volunteers and 20 PAH patients (WHO class II or III) were examined using a 1.5T MR scanner. Measurement of pulmonary perfusion was done in an inspiratory breathhold (FLASH3D; 3.5 mm x 1.9 mm x 4mm; TA per 3D dataset 1.5s). Injection of contrast media (0.1 mmol Gd-DTPA/kg BW) and image acquisition were started simultaneously. Evaluation of 3D perfusion was done using singular value decomposition. Lung borders were outlined manually. Each lung volume was divided into three regions (anterior, middle, posterior), and the following parameters were assessed: Time-to-Peak (TTP), blood flow (PBF), blood volume (PBV), and mean transit time (MTT). In 10 patients invasive pulmonary artery pressure measurements were available and correlated to the perfusion measurements. RESULTS: In both, controls and patients, an anterior-to-posterior gradient with higher PBF and PBV posterior was observed. In the posterior lung region, a significant difference (p<0.05) was found for TTP (12s versus 16s) and MTT (4s versus 6s) between volunteers and patients. PBF and PBV were lower in patients than in volunteers (i.e. dorsal regions: 124 versus 180 ml/100 ml/min and 10 versus 12 ml/100 ml), but the difference failed to be significant. The ratio of PBF and PBV between the posterior and the middle or ventral regions showed no difference between both groups. A moderate linear correlation between mean pulmonary arterial pressure (mPAP) and PBV (r=0.51) and MTT (r=0.56) was found. CONCLUSION: The only measurable effect of PAH on pulmonary perfusion is a prolonging of the MTT. There is only a moderate linear correlation of invasive mPAP with PBV and MTT.     

Quantitatively assessed dynamic contrast-enhanced magnetic resonance imaging in patients with chronic obstructive pulmonary disease: correlation of perfusion parameters with pulmonary function test and quantitative computed tomography

OBJECTIVES: The purpose of this study is to evaluate the correlation of the perfusion parameters of 3-dimensional, contrast-enhanced magnetic resonance (MR) imaging (3D CEMRI) with pulmonary function test (PFT) and quantitative computed tomography (CT) parameters in patients with chronic obstructive pulmonary disease (COPD). MATERIALS AND METHODS: In 14 patients with COPD, 3D CEMRI was performed. From the signal intensity-time curves, pulmonary blood flow (PBF), pulmonary blood volume (PBV), and mean transit time of each pixel was calculated. From the volumetric CT data, the quantitative parameters including the volume fraction of the lung below -950 Housefield Units (V(-950)) and mean lung density were assessed. The correlation between the MR perfusion parameters and the parameters from quantitative CT and PFT was assessed using Spearman correlation analysis. The correspondence of the regional impairment of perfusion on MR perfusion maps to the areas of emphysema on quantitative CT maps in each patient was assessed qualitatively using a 4-class visual scoring method by 2 readers. RESULTS: All 3D CEMRI examinations were successfully completed and MR perfusion parameters were obtained in all patients. The Spearman correlation test showed that PBF positively correlated with forced expiratory volume in 1 second (FEV(1))/forced vital capacity (FVC) (R = 0.49, P = 0.044), PBV positively correlated with FEV(1)/FVC (R = 0.69, P = 0.006) and negatively correlated with V-950 (R = -0.61, P = 0.020), and mean transit time positively correlated with FEV(1) (R = 0.63, P = 0.017) and FEV(1)/FVC (R = 0.76, P = 0.002). The areas of perfusion impairment on PBF and PBV maps were relatively well correlated with the areas of emphysema on CT maps [very good or good: PBF 71.5% (reader 1) and 64.3% (reader 2) of the patients, kappa = 0.47 (P < 0.001); PBV 78.6% (reader 1) and 78.6% (reader 2) of the patients, kappa = 0.89 (P < 0.001)]. CONCLUSIONS: This study shows that the deterioration of perfusion parameters measured on MR in patients with COPD, correlates with worsening of airflow limitation on PFT and emphysema index on CT. Regional heterogeneity of emphysema on CT matches with the decreased perfusion on MR.     

Quantitative evaluation of MR perfusion imaging using blood pool contrast agent in subjects without pulmonary diseases and in patients with pulmonary embolism

Objective

To assess the feasibility of time-resolved parallel three-dimensional magnetic resonance imaging (MRI) for quantitative analysis of pulmonary perfusion using a blood pool contrast agent.

Methods

Quantitative perfusion analysis was performed using novel software to assess pulmonary blood flow (PBF), pulmonary blood volume (PBV) and mean transit time (MTT) in a quantitative manner.

Results

The evaluation of lung perfusion in the normal subjects showed an increase of PBF, PBV ventrally to dorsally (gravitational direction), and the highest values at the upper lobe, with a decrease to the middle and lower lobe (isogravitational direction). MTT showed no relevant changes in either the gravitational or isogravitational directions. In comparison with normally perfused lung areas (in diseased patients), the pulmonary embolism (PE) regions showed a significantly lower mean PBF (20?±?0.6?ml/100?ml/min, normal region 94?±?1?ml/100?ml/min; P?P?P?Conclusion Our results demonstrate the feasibility of using time-resolved dynamic contrast-enhanced MRI to determine normal range and regional variation of pulmonary perfusion and perfusion deficits in patients with PE.

Key Points

? Recently introduced blood pool contrast agents improve MR evaluation of lung perfusion ? Regional differences in lung perfusion indicating a gravitational and isogravitational dependency. ? Focal areas of significantly decreased perfusion are detectable in pulmonary embolism.     

Assessment of differential pulmonary blood flow using perfusion magnetic resonance imaging: comparison with radionuclide perfusion scintigraphy

OBJECTIVES: We sought to assess the agreement between lung perfusion ratios calculated from pulmonary perfusion magnetic resonance imaging (MRI) and those calculated from radionuclide (RN) perfusion scintigraphy. MATERIALS AND METHODS: A retrospective analysis of MR and RN perfusion scans was conducted in 23 patients (mean age, 60 +/- 14 years) with different lung diseases (lung cancer = 15, chronic obstructive pulmonary disease = 4, cystic fibrosis = 2, and mesothelioma = 2). Pulmonary perfusion was assessed by a time-resolved contrast-enhanced 3D gradient-echo pulse sequence using parallel imaging and view sharing (TR = 1.9 milliseconds; TE = 0.8 milliseconds; parallel imaging acceleration factor = 2; partition thickness = 4 mm; matrix = 256 x 96; in-plane spatial resolution = 1.87 x 3.75 mm; scan time for each 3D dataset = 1.5 seconds), using gadolinium-based contrast agents (injection flow rate = 5 mL/s, dose = 0.1 mmol/kg of body weight). The peak concentration (PC) of the contrast agent bolus, the pulmonary blood flow (PBF), and blood volume (PBV) were computed from the signal-time curves of the lung. Left-to-right ratios of pulmonary perfusion were calculated from the MR parameters and RN counts. The agreement between these ratios was assessed for side prevalence (sign test) and quantitatively (Deming-regression). RESULTS: MR and RN ratios agreed on side prevalence in 21 patients (91%) with PC, in 20 (87%) with PBF, and in 17 (74%) with PBV. The MR estimations of left-to-right perfusion ratios correlated significantly with those of RN perfusion scans (P < 0.01). The correlation was higher using PC (r = 0.67) and PBF (r = 0.66) than using PBV (r = 0.50). The MR ratios computed from PBF showed the highest accuracy, followed by those from PC and PBV. Independently from the MR parameter used, in some patients the quantitative difference between the MR and RN ratios was not negligible. CONCLUSIONS: Pulmonary perfusion MRI can be used to assess the differential blood flow of the lung. Further studies in a larger group of patients are required to fully confirm the clinical suitability of this imaging method.     

Quantitative contrast‐enhanced perfusion measurements of the human lung using the prebolus approach

Purpose

To investigate dynamic contrast‐enhanced MRI (DCE‐MRI) for quantification of pulmonary blood flow (PBF) and blood volume (PBV) using the prebolus approach and to compare the results to the global lung perfusion (GLP).

Materials and Methods

Eleven volunteers were examined by applying different contrast agent doses (0.5, 1.0, 2.0, and 3.0 mL gadolinium diethylene triamine pentaacetic acid [Gd‐DTPA]), using a saturation‐recovery (SR) true fast imaging with steady precession (TrueFISP) sequence. PBF and PBV were determined for single bolus and prebolus. Region of interest (ROI) evaluation was performed and parameter maps were calculated. Additionally, cardiac output (CO) and lung volume were determined and GLP was calculated as a contrast agent–independent reference value.

Results

The prebolus results showed good agreement with low‐dose single‐bolus and GLP: PBF (mean ± SD in units of mL/minute/100 mL) = single bolus 190 ± 73 (0.5‐mL dose) and 193 ± 63 (1.0‐mL dose); prebolus 192 ± 70 (1.0–2.0‐mL dose) and 165 ± 52 (1.0–3.0‐mL dose); GLP (mL/minute/100 mL) = 187 ± 34. Higher single‐bolus resulted in overestimated values due to arterial input function (AIF) saturation.

Conclusion

The prebolus approach enables independent determination of appropriate doses for AIF and tissue signal. Using this technique, the signal‐to‐noise ratio (SNR) from lung parenchyma can be increased, resulting in improved PBF and PBV quantification, which is especially useful for the generation of parameter maps. J. Magn. Reson. Imaging 2009;30:104–111. © 2009 Wiley‐Liss, Inc.     

Dual Energy CT lung perfusion imaging--correlation with SPECT/CT

Objective

Aims were (1) to determine the diagnostic accuracy of Dual Energy CT (DECT) in the detection of perfusion defects and (2) to evaluate the potential of DECT to improve the sensitivity for PE.

Methods

15 patients underwent Dual Energy pulmonary CT angiography (DE CTPA) and a combination of lung perfusion SPECT/CT and ventilation scintigraphy. CTPA and DE iodine distribution maps as well as perfusion SPECT/CT and inhalation scintigrams were reviewed for pulmonary embolism (PE) diagnosis. DECT and SPECT perfusion images were assessed regarding localization and extent of perfusion defects. Diagnostic accuracy of DE iodine (perfusion) maps was determined with reference to SPECT/CT. Diagnostic accuracies for PE detection of DECT and of SPECT/CT with ventilation scintigraphy were calculated with reference to the consensus reading of all modalities.

Results

DE CTPA had a sensitivity/specificity of 100%/100% for acute PE, while the combination of SPECT/CT and ventilation scintigraphy had a sensitivity/specificity of 85.7%/87.5%. For perfusion defects, DECT iodine maps had a sensitivity/specificity of 76.7% and 98.2%.

Conclusion

DECT is able to identify pulmonary perfusion defects with good accuracy. This technique may potentially enhance the diagnostic accuracy in the assessment of PE.     

Acute and subacute dual energy CT findings of pulmonary embolism in rabbits: correlation with histopathology

Objective

The purpose of this study was to describe quantitative dual energy CT (DECT) findings and their accuracy in the detection of acute and subacute pulmonary embolism (PE) in rabbits.

Methods

Pulmonary emboli were created in 24 rabbits by gelatin sponge femoral vein injection. Conventional CT pulmonary angiography (CTPA) and DECT were obtained at either 2 h, 1 day, 3 days or 7 days after embolisation (n=6 rabbits for each time point). The location and number of PEs in the different stages were recorded at CTPA and iodine maps from DECT on a per-lobe basis. With histopathology as the reference standard, sensitivity and specificity of CTPA and DECT were calculated. CT and iodine map overlay values of the embolic and non-embolic areas were measured for each scan.

Results

With histopathology as the reference standard, the overall sensitivity and specificity of CTPA were 98% and 100% and those of iodine maps were 100% and 95%, respectively. Conventional CT and iodine map values of the embolised and non-embolised areas were significantly different between 2 h and 1 day (p<0.001), but not between 3 days and 7 days (p>0.05). A statistical difference was found for overlay values measured in the embolic and non-embolic regions for four groups.

Conclusion

Iodine maps derived from DECT show alterations in lung perfusion for acute and subacute PE in an experimental rabbit model and show comparable sensitivity for PE detection and conventional CTPAIn the USA, more than 650 000 cases of pulmonary embolism (PE) occur each year, resulting in as many as 300 000 annual fatalities [1,2]. Despite the high morbidity, the diagnosis of PE may be delayed in the absence of typical clinical symptoms or when emboli are subsegmental and such scenarios may delay the treatment and increase the mortality of PE. Imaging plays an important role in the diagnosis and follow-up of PE. With improvements in multidetector row CT, CT pulmonary angiography (CTPA) has largely replaced digital subtraction angiography (DSA) for the diagnosis and follow-up of PE and has been recommended as the reference of standard for diagnosis of acute PE [3]. However, CTPA has shortcomings, such as a limited sensitivity to detect peripheral or subsubsegmental emboli of the pulmonary artery and an inability to show lung perfusion impairment resulting from acute or chronic PE.With the development of dual source CT (DSCT), in which two orthogonally mounted detectors and tubes arrays operate simultaneously and can be set to different tube potentials to allow for dual energy CT (DECT) acquisitions with minimal patient motion registration artefact, DECT imaging has been used to investigate iodine distribution maps in clinical and pre-clinical studies [4-13]. Such iodine maps, which have been termed blood flow imaging (BFI), have been shown to be valuable supplements to conventional anatomic CTPA for the evaluation of distal pulmonary artery emboli [4-13]. Many studies have focused on the feasibility or diagnostic accuracy of DECT iodine maps to improve the detection of PE, with CTPA, scintigraphy or histopathology as a reference standard in the clinical and experimental studies [5-13], or the evaluation of image quality of dual energy CTPA [14,15]. However, to the best of our knowledge, there are no reports that describe the evolution of CT and DECT imaging findings of PE over time after an embolic event with histopathological correlation. Histopathology correlation is most ethically obtained using an animal model. Therefore, we evaluated DECT findings with histopathology correlation in a rabbit model of PE with different time delays after embolisation and assessed the diagnostic accuracy of DECT in the detection of PE at these different time points.     

Suppression of pulmonary vasculature in lung perfusion MRI using correlation analysis

The purpose of the study was to evaluate the feasibility of suppressing the pulmonary vasculature in lung perfusion MRI using cross-correlation analysis (CCA). Perfusion magnetic resonance imaging (MRI) (3D FLASH, TR/TE/flip angle: 0.8 ms/2.1 ms/40°) of the lungs was performed in seven healthy volunteers at 1.5 Tesla after injection of Gd-DTPA. CCA was performed pixel-wise in lung segmentations using the signal time-course of the main pulmonary artery and left atrium as references. Pixels with high correlation coefficients were considered as arterial or venous and excluded from further analysis. Quantitative perfusion parameters [pulmonary blood flow (PBF) and volume (PBV)] were calculated for manual lung segmentations separately, with the entire left and right lung with all intrapulmonary vessels (IPV) included, excluded manually or excluded using CCA. The application of CCA allowed reliable suppression of hilar and large IPVs. Using vascular suppression by CCA, perfusion parameters were significantly reduced (p ≤ 0.001). The reduction was 8% for PBF and 13% for PBV compared with manual exclusion and 15% for PBF and 25% for PBV when all vessel structures were included. The application of CCA improves the visualisation and quantification of lung perfusion in MRI. Overestimation of perfusion parameters caused by pulmonary vessels is significantly reduced.     

Imaging of acute pulmonary embolism using a dual energy CT system with rapid kVp switching: Initial results

Purpose

Computed tomography pulmonary angiography (CTPA) is considered as clinical gold standard for diagnosing pulmonary embolism (PE). Whereas conventional CTPA only offers anatomic information, dual energy CT (DECT) provides functional information on blood volume as surrogate of perfusion by assessing the pulmonary iodine distribution. The purpose of this study was to evaluate the feasibility of lung perfusion imaging using a single-tube DECT scanner with rapid kVp switching.

Materials and methods

Fourteen patients with suspicion of acute PE underwent DECT. Two experienced radiologists assessed the CTPA images and lung perfusion maps regarding the presence of PE. The image quality was rated using a semi-quantitative 5-point scale: 1 (=excellent) to 5 (=non-diagnostic). Iodine concentrations were quantified by a ROI analysis.

Results

Seventy perfusion defects were identified in 266 lung segments: 13 (19%) were rated as consistent with PE. Five patients had signs of PE at CTPA. All patients with occlusive clots were correctly identified by DECT perfusion maps. On a per patient basis the sensitivity and specificity were 80.0% and 88.9%, respectively, while on a per segment basis it was 40.0% and 97.6%, respectively. None of the patients with a homogeneous perfusion map had an abnormal CTPA. The overall image quality of the perfusion maps was rated with a mean score of 2.6 ± 0.6. There was a significant ventrodorsal gradient of the median iodine concentrations (1.1 mg/cm³ vs. 1.7 mg/cm³).

Conclusion

Lung perfusion imaging on a DE CT-system with fast kVp-switching is feasible. DECT might be a helpful adjunct to assess the clinical severity of PE.     

High temporal versus high spatial resolution in MR quantitative pulmonary perfusion imaging of two-year old children after congenital diaphragmatic hernia repair

Objectives

Congenital diaphragmatic hernia (CDH) leads to lung hypoplasia. Using dynamic contrast-enhanced (DCE) MR imaging, lung perfusion can be quantified. As MR perfusion values depend on temporal resolution, we compared two protocols to investigate whether ipsilateral lung perfusion is impaired after CDH, whether there are protocol-dependent differences, and which protocol is preferred.

Methods

DCE-MRI was performed in 36 2-year old children after CDH on a 3 T MRI system; protocol A (n?=?18) based on a high spatial (3.0 s; voxel: 1.25 mm³) and protocol B (n?=?18) on a high temporal resolution (1.5 s; voxel: 2 mm³). Pulmonary blood flow (PBF), pulmonary blood volume (PBV), mean transit time (MTT), and peak-contrast-to-noise-ratio (PCNR) were quantified.

Results

PBF was reduced ipsilaterally, with ipsilateral PBF of 45?±?26 ml/100 ml/min to contralateral PBF of 63?±?28 ml/100 ml/min (p?=?0.0016) for protocol A; and for protocol B, side differences were equivalent (ipsilateral PBF?=?62?±?24 vs. contralateral PBF?=?85?±?30 ml/100 ml/min; p?=?0.0034). PCNR was higher for protocol B (30?±?18 vs. 20?±?9; p?=?0.0294). Protocol B showed higher values of PBF in comparison to protocol A (p always <0.05).

Conclusions

Ipsilateral lung perfusion is reduced in 2-year old children following CDH repair. Higher temporal resolution and increased voxel size show a gain in PCNR and lead to higher perfusion values. Protocol B is therefore preferred.

Key Points

? Quantitative lung perfusion parameters depend on temporal and spatial resolution. ? Reduction of lung perfusion in CDH can be measured with different MR protocols. ? Temporal resolution of 1.5 s with spatial resolution of 2 mm ³ is suitable.     

Perfusion characterization of liver metastases from endocrine tumors: Computed tomography perfusion

AIM: To assess prospectively parameters of computed tomography perfusion (CT p) for evaluation of vascularity of liver metastases from neuroendocrine tumors.METHODS: This study was approved by the hospital’s institutional review board. All 18 patients provided informed consent. There were 30 liver metastases from neuroendocrine tumors. Patients were divided into three groups depending on the appearance of the liver metastases at the arterial phase of morphological CT (hyperdense, hypodense and necrotic). Sequential acquisition of the liver was performed before and for 2 min after intravenous injection of 0.5 mg/kg contrast medium, at 4 mL/s. Data were analyzed using deconvolution analysis to calculate blood flow (BF), blood volume (BV), mean transit time (MTT), hepatic arterial perfusion index (HAPI) and a bi-compartmental analysis was performed to obtain vascular permeability-surface area product (PS). Post-treatment analysis was performed by a radiologist and regions of interest were plotted on the metastases, normal liver, aorta and portal vein.RESULTS: At the arterial phase of the morphological CT scan, the aspects of liver metastases were hyperdense (n = 21), hypodense (n = 7), and necrotic (n = 2). In cases of necrotic metastases, none of the CT p parameters were changed. Compared to normal liver, a significant difference in all CT p parameters was found in cases of hyperdense metastases, and only for HAPI and MTT in cases of hypodense metastases. No significant difference was found for MTT and HAPI between hypo- and hyperdense metastases. A significant decrease of PS, BV and BF was demonstrated in cases of patients with hypodense lesions PS (23 ± 11.6 mL/100 g per minute) compared to patients with hyperdense lesions; PS (13.5 ± 10.4 mL/100 g per minute), BF (93.7 ± 75.4 vs 196.0 ± 115.6 mL/100 g per minute) and BV (9.7 ± 5.9 vs 24.5 ± 10.9 mL/100 g).CONCLUSION: CT p provides additional information compared to the morphological appearance of liver metastases.     

Dual-bolus approach to quantitative measurement of pulmonary perfusion by contrast-enhanced MRI

PURPOSE: To evaluate a dual-bolus approach to pulmonary perfusion MRI. MATERIALS AND METHODS: The dual-bolus approach uses a separate low-dose measurement for the arterial input function (AIF) to ensure linearity. The measured AIF is constructed according to a subsequent higher dose used for the tissue concentration curves in the lung. In this study a prebolus of 0.01 mmol/kg followed by doses of 0.04 mmol/kg and 0.08 mmol/kg was used. Measurements were performed using time-resolved two-dimensional fast low-angle shot (2D FLASH) MRI (TE/TR = 0.73 msec/1.73 msec; flip angle = 40 degrees ; generalized autocalibrating partially parallel acquisitions (GRAPPA) factor = 3; temporal resolution = 400 msec) in end-inspiratory breath-hold. RESULTS: The combination of prebolus/0.04 mmol/kg resulted in a pulmonary blood flow (PBF) of 211 +/- 77 mL/min/100 mL, and a pulmonary blood volume (PBV) of 20 +/- 3 mL/100 mL. The combination of prebolus/0.08 mmol/kg resulted in approximately 50% lower perfusion values, most likely due to saturation effects in the lung tissue. CONCLUSION: A dual-bolus approach to pulmonary perfusion MRI is feasible and may reduce the problem of lacking linear relationship between the contrast-agent concentration and signal intensity.     

Dual energy CT for the assessment of lung perfusion—Correlation to scintigraphy

Purpose of this study was to determine the diagnostic value of dual energy CT in the assessment of pulmonary perfusion with reference to pulmonary perfusion scintigraphy.Thirteen patients received both dual energy CT (DECT) angiography (Somatom Definition, Siemens) and ventilation/perfusion scintigraphy. Median time between scans was 3 days (range, 0–90). DECT perfusion maps were generated based on the spectral properties of iodine. Two blinded observes assessed DECT angiograms, perfusion maps and scintigrams for presence and location of perfusion defects. The results were compared by patient and by segment, and diagnostic accuracy of DECT perfusion imaging was calculated regarding scintigraphy as standard of reference.Diagnostic accuracy per patient showed 75% sensitivity, 80% specificity and a negative predictive value of 66%. Sensitivity per segment amounted to 83% with 99% specificity, with 93% negative predictive value. Peripheral parts of the lungs were not completely covered by the 80 kVp detector in 85% of patients. CTA identified corresponding emboli in 66% of patients with concordant perfusion defects in DECT and scintigraphy.Dual energy CT perfusion imaging is able to display pulmonary perfusion defects with good agreement to scintigraphic findings. DECT can provide a pulmonary CT angiogram, high-resolution morphology of the lung parenchyma and perfusion information in one single exam.     

Region of interest-based versus whole-lung segmentation-based approach for MR lung perfusion quantification in 2-year-old children after congenital diaphragmatic hernia repair

Objective

With a region of interest (ROI)-based approach 2-year-old children after congenital diaphragmatic hernia (CDH) show reduced MR lung perfusion values on the ipsilateral side compared to the contralateral. This study evaluates whether results can be reproduced by segmentation of whole-lung and whether there are differences between the ROI-based and whole-lung measurements.

Methods

Using dynamic contrast-enhanced (DCE) MRI, pulmonary blood flow (PBF), pulmonary blood volume (PBV) and mean transit time (MTT) were quantified in 30 children after CDH repair. Quantification results of an ROI-based (six cylindrical ROIs generated of five adjacent slices per lung-side) and a whole-lung segmentation approach were compared.

Results

In both approaches PBF and PBV were significantly reduced on the ipsilateral side (p always <0.0001). In ipsilateral lungs, PBF of the ROI-based and the whole-lung segmentation-based approach was equal (p=0.50). In contralateral lungs, the ROI-based approach significantly overestimated PBF in comparison to the whole-lung segmentation approach by approximately 9.5 % (p=0.0013).

Conclusions

MR lung perfusion in 2-year-old children after CDH is significantly reduced ipsilaterally. In the contralateral lung, the ROI-based approach significantly overestimates perfusion, which can be explained by exclusion of the most ventral parts of the lung. Therefore whole-lung segmentation should be preferred.

Key Points

? Ipsilaterally, absolute lung perfusion after CDH is reduced in whole-lung analysis. ? Ipsilaterally, the ROI- and whole-lung-based approaches generate identical results. ? Contralaterally, the ROI-based approach significantly overestimates perfusion results. ? Whole lung should be analysed in MR lung perfusion imaging. ? MR lung perfusion measurement is a radiation-free parameter of lung function.

     

Dual energy CT for the assessment of lung perfusion--correlation to scintigraphy

Purpose of this study was to determine the diagnostic value of dual energy CT in the assessment of pulmonary perfusion with reference to pulmonary perfusion scintigraphy. Thirteen patients received both dual energy CT (DECT) angiography (Somatom Definition, Siemens) and ventilation/perfusion scintigraphy. Median time between scans was 3 days (range, 0-90). DECT perfusion maps were generated based on the spectral properties of iodine. Two blinded observes assessed DECT angiograms, perfusion maps and scintigrams for presence and location of perfusion defects. The results were compared by patient and by segment, and diagnostic accuracy of DECT perfusion imaging was calculated regarding scintigraphy as standard of reference. Diagnostic accuracy per patient showed 75% sensitivity, 80% specificity and a negative predictive value of 66%. Sensitivity per segment amounted to 83% with 99% specificity, with 93% negative predictive value. Peripheral parts of the lungs were not completely covered by the 80 kVp detector in 85% of patients. CTA identified corresponding emboli in 66% of patients with concordant perfusion defects in DECT and scintigraphy. Dual energy CT perfusion imaging is able to display pulmonary perfusion defects with good agreement to scintigraphic findings. DECT can provide a pulmonary CT angiogram, high-resolution morphology of the lung parenchyma and perfusion information in one single exam.     

Assessment of pulmonary parenchyma perfusion with FAIR in comparison with DCE-MRI--initial results

Objective

The aim of this study was to assess pulmonary parenchyma perfusion with flow-sensitive alternating inversion recovery (FAIR) in comparison with 3D dynamic contrast-enhanced (DCE) imaging in healthy volunteers and in patients with pulmonary embolism or lung cancer.

Materials and methods

Sixteen healthy volunteers and 16 patients with pulmonary embolism (5 cases) or lung cancer (11 cases) were included in this study. Firstly, the optimized inversion time of FAIR (TI) was determined in 12 healthy volunteers. Then, FAIR imaging with the optimized TI was performed followed by DCE-MRI on the other 4 healthy volunteers and 16 patients. Tagging efficiency of lung and SNR of perfusion images were calculated with different TI values. In the comparison of FAIR with DCE-MRI, the homogeneity of FAIR and DCE-MRI perfusion was assessed. In the cases of perfusion abnormality, the contrast between normal lung and perfusion defects was quantified by calculating a normalized signal intensity ratio.

Results

One thousand milliseconds was the optimal TI, which generated the highest lung tagging efficiency and second highest PBF SNR. In the volunteers, the signal intensity of perfusion images acquired with both FAIR and DCE-MRI was homogeneous. Wedged-shaped or triangle perfusion defects were visualized in five pulmonary embolisms and three lung cancer cases. There was no significant statistical difference in signal intensity ratio between FAIR and DCE-MRI (P > 0.05). In the rest of eight lung cancers, all the lesions showed low perfusion against the higher perfused pulmonary parenchyma in both FAIR and DCE-MRI.

Conclusion

Pulmonary parenchyma perfusion imaging with FAIR was feasible, consistent and could obtain similar functional information to that from DCE-MRI.     

Comparing dual energy CT and subtraction CT on a phantom: which one provides the best contrast in iodine maps for sub-centimetre details?

Objectives

To compare contrast-to-noise ratios (CNRs) and iodine discrimination thresholds on iodine maps derived from dual energy CT (DECT) and subtraction CT (SCT).

Methods

A contrast-detail phantom experiment was performed with 2 to 15 mm diameter tubes containing water or iodinated contrast concentrations ranging from 0.5 mg/mL to 20 mg/mL. DECT scans were acquired at 100 kVp and at 140 kVp+Sn filtration. SCT scans were acquired at 100 kVp. Iodine maps were created by material decomposition (DECT) or by subtraction of water scans from iodine scans (SCT). Matched exposure levels varied from 8 to 15 mGy. Iodine discrimination thresholds (C_r) and response times were determined by eight observers.

Results

The adjusted mean CNR was 1.9 times higher for SCT than for DECT. Exposure level had no effect on CNR. All observers discriminated all details ≥10 mm at 12 and 15 mGy. For sub-centimetre details, the lowest calculated C_r was ≤ 0.50 mg/mL for SCT and 0.64 mg/mL for DECT. The smallest detail was discriminated at ≥4.4 mg/mL with SCT and at ≥7.4 mg/mL with DECT. Response times were lower for SCT than DECT.

Conclusions

SCT results in higher CNR and reduced iodine discrimination thresholds compared to DECT for sub-centimetre details.

Key Points

? Subtraction CT iodine maps exhibit higher CNR than dual-energy iodine maps ? Lower iodine concentrations can be discriminated for sub-cm details with SCT ? Response times are lower using SCT compared to dual-energy CT