Patient-tailored risk assessment of obstructive coronary artery disease using Rubidium-82 PET-based myocardial flow quantification with visual interpretation

INTRODUCTION

Our aim was to estimate the probability of obstructive CAD (oCAD) for an individual patient as a function of the myocardial flow reserve (MFR) measured with Rubidium-82 (Rb-82) PET in patients with a visually normal or abnormal scan.

MATERIALS AND METHODS

We included 1519 consecutive patients without a prior history of CAD referred for rest-stress Rb-82 PET/CT. All images were visually assessed by two experts and classified as normal or abnormal. We estimated the probability of oCAD for visually normal scans and scans with small (5%-10%) or larger defects (> 10%) as function of MFR. The primary endpoint was oCAD on invasive coronary angiography, when available.

RESULTS

1259 scans were classified as normal, 136 with a small defect and 136 with a larger defect. For the normal scans, the probability of oCAD increased exponentially from 1% to 10% when segmental MFR decreased from 2.1 to 1.3. For scans with small defects, the probability increased from 13% to 40% and for larger defects from 45% to > 70% when segmental MFR decreased from 2.1 to 0.7.

CONCLUSION

Patients with > 10% risk of oCAD can be distinguished from patients with < 10% risk based on visual PET interpretation only. However, there is a strong dependence of MFR on patient's individual risk of oCAD. Hence, combining both visual interpretation and MFR results in a better individual risk assessment which may impact treatment strategy.

Machine learning based model to diagnose obstructive coronary artery disease using calcium scoring, PET imaging, and clinical data

INTRODUCTION

Accurate risk stratification in patients with suspected stable coronary artery disease is essential for choosing an appropriate treatment strategy. Our aim was to develop and validate a machine learning (ML) based model to diagnose obstructive CAD (oCAD).

METHOD

We retrospectively have included 1007 patients without a prior history of CAD who underwent CT-based calcium scoring (CACS) and a Rubidium-82 PET scan. The entire dataset was split 4:1 into a training and test dataset. An ML model was developed on the training set using fivefold stratified cross-validation. The test dataset was used to compare the performance of expert readers to the model. The primary endpoint was oCAD on invasive coronary angiography (ICA).

RESULTS

ROC curve analysis showed an AUC of 0.92 (95% CI 0.90-0.94) for the training dataset and 0.89 (95% CI 0.84-0.93) for the test dataset. The ML model showed no significant differences as compared to the expert readers (p ≥ 0.03) in accuracy (89% vs. 88%), sensitivity (68% vs. 69%), and specificity (92% vs. 90%).

CONCLUSION

The ML model resulted in a similar diagnostic performance as compared to expert readers, and may be deployed as a risk stratification tool for obstructive CAD. This study showed that utilization of ML is promising in the diagnosis of obstructive CAD.

Automatic identification and segmentation of slice of minimal hiatal dimensions in transperineal ultrasound volumes

OBJECTIVE

To develop and validate a tool for automatic selection of the slice of minimal hiatal dimensions (SMHD) and segmentation of the urogenital hiatus (UH) in transperineal ultrasound (TPUS) volumes.

METHODS

Manual selection of the SMHD and segmentation of the UH was performed in TPUS volumes of 116 women with symptomatic pelvic organ prolapse (POP). These data were used to train two deep-learning algorithms. The first algorithm was trained to provide an estimation of the position of the SMHD. Based on this estimation, a slice was selected and fed into the second algorithm, which performed automatic segmentation of the UH. From this segmentation, measurements of the UH area (UHA), anteroposterior diameter (APD) and coronal diameter (CD) were computed automatically. The mean absolute distance between manually and automatically selected SMHD, the overlap (dice similarity index (DSI)) between manual and automatic UH segmentation and the intraclass correlation coefficient (ICC) between manual and automatic UH measurements were assessed on a test set of 30 TPUS volumes.

RESULTS

The mean absolute distance between manually and automatically selected SMHD was 0.20 cm. All DSI values between manual and automatic UH segmentations were above 0.85. The ICC values between manual and automatic UH measurements were 0.94 (95% CI, 0.87-0.97) for UHA, 0.92 (95% CI, 0.78-0.97) for APD and 0.82 (95% CI, 0.66-0.91) for CD, demonstrating excellent agreement.

CONCLUSIONS

Our deep-learning algorithms allowed reliable automatic selection of the SMHD and UH segmentation in TPUS volumes of women with symptomatic POP. These algorithms can be implemented in the software of TPUS machines, thus reducing clinical analysis time and simplifying the examination of TPUS data for research and clinical purposes. © 2021 The Authors. Ultrasound in Obstetrics &amp; Gynecology published by John Wiley &amp; Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Effect of temporal sampling protocols on myocardial blood flow measurements using Rubidium-82 PET

BACKGROUND

A variety of temporal sampling protocols is used worldwide to measure myocardial blood flow (MBF). Both the length and number of time frames in these protocols may alter MBF and myocardial flow reserve (MFR) measurements. We aimed to assess the effect of different clinically used temporal sampling protocols on MBF and MFR quantification in Rubidium-82 (Rb-82) PET imaging.

METHODS

We retrospectively included 20 patients referred for myocardial perfusion imaging using Rb-82 PET. A literature search was performed to identify appropriate sampling protocols. PET data were reconstructed using 14 selected temporal sampling protocols with time frames of 5-10 seconds in the first-pass phase and 30-120 seconds in the tissue phase. Rest and stress MBF and MFR were calculated for all protocols and compared to the reference protocol with 26 time frames.

RESULTS

MBF measurements differed (P ≤ 0.003) in six (43%) protocols in comparison to the reference protocol, with mean absolute relative differences up to 16% (range 5%-31%). Statistically significant differences were most frequently found for protocols with tissue phase time frames < 90 seconds. MFR did not differ (P ≥ 0.11) for any of the protocols.

CONCLUSIONS

Various temporal sampling protocols result in different MBF values using Rb-82 PET. MFR measurements were more robust to different temporal sampling protocols.

Value of SiPM PET in myocardial perfusion imaging using Rubidium-82

BACKGROUND

PET scanners using silicon photomultipliers with digital readout (SiPM PET) have an improved temporal and spatial resolution compared to PET scanners using conventional photomultiplier tubes (PMT PET). However, the effect on image quality and visibility of perfusion defects in myocardial perfusion imaging (MPI) is unknown. Our aim was to determine the value of a SiPM PET scanner in MPI.

METHODS

We prospectively included 30 patients who underwent rest and regadenoson-induced stress Rubidium-82 (Rb-82) MPI on the D690 PMT PET (GE Healthcare) and within three weeks on the Vereos SiPM PET (Philips Healthcare). Two expert readers scored the image quality and assessed the existence of possible defects. In addition, interpreter's confidence, myocardial blood flow (MBF), and myocardial flow reserve (MFR) values were compared.

RESULTS

Image quality improved (P = 0.03) using the Vereos as compared to the D690. Image quality of the Vereos and the D690 was graded fair in 20% and 10%, good in 60% and 50%, and excellent in 20% and 40%, respectively. Defect interpretation and interpreter's confidence did not differ between the D690 and the Vereos (P > 0.50). There were no significant differences in rest MBF (P ≥ 0.29), stress MBF (P ≥ 0.11), and MFR (P ≥ 0.51).

CONCLUSION

SiPM PET provides an improved image quality in comparison with PMT PET. Defect interpretation, interpreter's confidence, and absolute blood flow measurements were comparable between both systems. SiPM PET is therefore a reliable technique for MPI using Rb-82.

TRIAL REGISTRATION

ToetsingOnline NL63853.075.17. Registered 13 November, 2017.

Body weight-dependent Rubidium-82 activity results in constant image quality in myocardial perfusion imaging with PET

BACKGROUND

Clinical practice shows degrading image quality in heavier patients who undergo myocardial perfusion imaging (MPI) with Rubidium-82 (Rb-82) PET when using a fixed tracer activity. Our aim was to derive and validate a patient-specific activity protocol resulting in a constant image quality in PET MPI.

METHODS

We included 251 patients who underwent rest MPI with Rb-82 PET (Discovery 670, GE Healthcare). 132 patients were included retrospectively and were scanned using a fixed activity of 740 MBq. The total number of measured prompts was normalized to activity and correlated to body weight, mass per body length and body mass index to find the best predicting parameter. Next, a patient-specific activity was derived and subsequently validated in 119 additional patients. Image quality was scored by three experts on a four-point scale.

RESULTS

Both image quality and prompts decreased in heavier patients when using a fixed activity (p < .005). Body weight was used to derive a new activity formula: Activity = 8.3 MBq/kg. When applying this formula, both measured prompts and scored image quality became independent of body weight (p > .60).

CONCLUSION

Administrating a Rb-82 activity that linearly depends on body weight resulted in a constant image quality across all patients and is recommended.

Value of regional myocardial flow measurements using Rubidium-82 PET

Funding Acknowledgements

Type of funding sources: None.

Introduction

The combination of myocardial blood flow (MBF) measurements using Rubidium-82 (Rb-82) PET and visual assessment of the PET images is increasingly used due to its high diagnostic and prognostic value. Typically, flow measurements are calculated and used for the myocardium as a whole (global). However, small regional flow deficits may go unnoticed when only looking at global flow values.

Purpose

To compare the diagnostic value of regional and global myocardial flow measurements using Rb-82 PET in the detection of obstructive CAD.

Methods

 We retrospectively included 1034 patients with no history of coronary artery disease (CAD) referred for rest and regadenoson-induced stress Rb-82 PET/CT. MBFs were calculated using Lortie’s one-tissue compartment model. Myocardial flow reserve (MFR) was calculated as the ratio of MBF during stress and rest. Regional flow was determined per vessel and per segment. Vessel MFR was defined as the lowest flow reserve of LAD, LCX and RCA territories and segmental MFR as the lowest flow reserve in all 17 segments. Follow-up data were obtained from medical records. Patients were classified to have obstructive CAD if follow-up included a positive invasive coronary angiography (ICA), percutaneous coronary intervention (PCI), coronary artery bypass grafting (CABG) or all cause death. Receiver-operating characteristic (ROC) analyses were constructed to compare the diagnostic value of global and regional flow values.

Results

Follow-up was obtained in all 1034 patients and the median follow-up time was 2.1 years. Myocardial flow reserve values were significantly lower (p &lt; 0.001) in the 128 patients classified with obstructive CAD than in the 906 patients without obstructive CAD: global MFR  (median 1.9 [interquartile range 1.6-2.4] vs. 2.5 [2.1-2.9]); vessel MFR (1.6 [1.3-2.1]  vs. 2.3 [1.9-2.6]); Segmental MFR (1.3 [0.9-1.7] vs. 1.9 [1.6-2.2]). The area under the curve of vessel MFR (0.79 ± 0.02) and segmental MFR (0.81 ± 0.02) were similar but significantly (p &lt; 0.001) larger than the area of global MFR (0.75 ± 0.03), as shown in the Figure.

Conclusion

The diagnostic value improved with the use of regional MFR instead of global MFR measurements in the detection of obstructive CAD. Therefore, it seems that visual assessment of PET images can best be combined with regional flow measurements either on a per vessel or a per segment basis in Rubidium-82 PET myocardial perfusion imaging.

Prediction of obstructive coronary artery disease after Rb-82 PET myocardial perfusion imaging and coronary artery calcium scoring using machine learning

Funding Acknowledgements

Type of funding sources: None.

Background

Accurate risk stratification in patients with suspected stable coronary artery disease (CAD) is essential for choosing an appropriate treatment strategy but remains challenging in clinical practice.

Purpose

Our aim was to develop and validate a risk model to predict the presence of obstructive CAD after Rubidium-82 PET and a coronary artery calcium score (CACS) scan using a machine learning (ML) algorithm.

Methods

We retrospectively included 1007 patients without prior cardiovascular history and  a low-intermediate pre-test likelihood, referred for rest and regadenoson-induced stress Rubidium-82 PET combined with a CACS scan. Multiple features were included in the ML model; PET derived features such as summed difference score and flow values, CACS, cardiovascular risk factors (cigarette smoking, hypertension, hypercholesterolemia, diabetes, positive family history of CAD), medication; age; gender; body mass index; creatinine serum values; and visual PET interpretation. An XGBoost ML algorithm was developed using a subset of 805 patients to predict obstructive CAD by using 5-fold cross validation in combination with a grid search. Obstructive CAD during follow-up was defined as a significant stenosis during invasive coronary angiography, a percutaneous coronary intervention or a coronary artery bypass graft procedure. The ML algorithm was validated with unseen data of the remaining 202 patients.

Results

Application of the XGBoost algorithm resulted in an area under the curve (AUC) of 0.93 using the training data (n = 805) and an AUC of 0.89 using the unseen data (n = 202) in predicting obstructive CAD. The strongest predictors were the CAC-scores and quantitative PET derived features. The classical risk factors and medication hardly provided an added value in the prediction of obstructive CAD.

Conclusion

The developed ML algorithm is able to provide individualized risk stratification by predicting the probability of obstructive CAD.  Although validation with a larger dataset could result in a more well defined performance range, this model already shows potential to be implemented in the diagnostic workflow.

Early differences in dynamic uptake of 68Ga-PSMA-11 in primary prostate cancer: A test-retest study

INTRODUCTION

Dynamic PET/CT allows visualization of pharmacokinetics over the time, in contrast to static whole body PET/CT. The objective of this study was to assess 68Ga-PSMA-11 uptake in pathological lesions and benign tissue, within 30 minutes after injection in primary prostate cancer (PCa) patients in test-retest setting.

MATERIALS AND METHODS

Five patients, with biopsy proven PCa, were scanned dynamically in list mode for 30 minutes on a digital PET/CT-scanner directly after an intravenous bolus injection of 100 MBq 68Ga-PSMA-11. Approximately 45 minutes after injection a static whole body scan was acquired, followed by a one bed position scan of the pelvic region. The scans were repeated approximately four weeks later, without any intervention in between. Semi-quantitative assessment was performed using regions-of-interest in the prostate tumor, bladder, gluteal muscle and iliac artery. Time-activity curves were extracted from the counts in these regions and the intra-patient variability between both scans was assessed.

RESULTS

The uptake of the iliac artery and gluteal muscle reached a plateau after 5 and 3 minutes, respectively. The population fell apart in two groups with respect to tumor uptake: in some patients the tumor uptake reached a plateau after 5 minutes, whereas in other patients the uptake kept increasing, which correlated with larger tumor volumes on PET/CT scan. Median intra-patient variation between both scans was 12.2% for artery, 9.7% for tumor, 32.7% for the bladder and 14.1% for the gluteal muscle.

CONCLUSION

Dynamic 68Ga-PSMA-11 PET/CT scans, with a time interval of four weeks, are reproducible with a 10% variation in uptake in the primary prostate tumor. An uptake plateau was reached for the iliac artery and gluteal muscle within 5 minutes post-injection. A larger tumor volume seems to be related to continued tumor uptake. This information might be relevant for both response monitoring and PSMA-based radionuclide therapies.

A review on imaging techniques and quantitative measurements for dynamic imaging of cerebral aneurysm pulsations

Measurement of intracranial aneurysm wall motion may refine the current rupture risk estimation. A golden standard for measuring aneurysm pulsation is lacking. The aim is to evaluate magnitudes of aneurysm pulsation as published in current literature. Embase and PubMed were searched for publications containing quantitative measures of cardiac-cycle related cerebral aneurysm pulsation (no date or language restrictions). Eleven studies were included, covering 197 unruptured and untreated cerebral aneurysms. Quantitative pulsation measurements were extracted from the studies. Characteristics of the study population and aneurysms were taken into account, as well as the imaging modality, scanning technique and data processing methods used. A meta-analysis was performed of studies with similar methodologies and individual IA measures and locations. The magnitude of the absolute volume pulsations varied between 14 ± 9 mm³ and 106 ± 123 mm³ and the mean relative volume change varied between 5 and 36%. The meta-analysis revealed a positive correlation between size and absolute volume change. The relative volume change in Basilar artery aneurysms seems smaller. No authors were contacted for original study data and articles only describing visual pulsations were excluded. The variation in methodologies impedes an accurate estimation of the magnitude of IA pulsations. Validation of aneurysm pulsation measurement is crucial prior to clinical studies evaluating IA pulsatility in relation to IA rupture risk. Prerequisite is a reliable and robust imaging method with high spatial and temporal resolution and standardization of the image analysis methods.

Clinical value of machine learning-based interpretation of I-123 FP-CIT scans to detect Parkinson's disease: a two-center study

PURPOSE

Our aim was to develop and validate a machine learning (ML)-based approach for interpretation of I-123 FP-CIT SPECT scans to discriminate Parkinson's disease (PD) from non-PD and to determine its generalizability and clinical value in two centers.

METHODS

We retrospectively included 210 consecutive patients who underwent I-123 FP-CIT SPECT imaging and had a clinically confirmed diagnosis. Linear support vector machine (SVM) was used to build a classification model to discriminate PD from non-PD based on I-123-FP-CIT striatal uptake ratios, age and gender of 90 patients. The model was validated on unseen data from the same center where the model was developed (n = 40) and consecutively on data from a different center (n = 80). Prediction performance was assessed and compared to the scan interpretation by expert physicians.

RESULTS

Testing the derived SVM model on the unseen dataset (n = 40) from the same center resulted in an accuracy of 95.0%, sensitivity of 96.0% and specificity of 93.3%. This was identical to the classification accuracy of nuclear medicine physicians. The model was generalizable towards the other center as prediction performance did not differ thereby obtaining an accuracy of 82.5%, sensitivity of 88.5% and specificity of 71.4% (p = NS). This was comparable to that of nuclear medicine physicians (p = NS).

CONCLUSION

ML-based interpretation of I-123-FP-CIT scans results in accurate discrimination of PD from non-PD similar to visual assessment in both centers. The derived SVM model is therefore generalizable towards centers using comparable acquisition and image processing methods and implementation as diagnostic aid in clinical practice is encouraged.

A Systematic Review for the Design of In Vitro Flow Studies of the Carotid Artery Bifurcation

PURPOSE

In vitro blood flow studies in carotid artery bifurcation models may contribute to understanding the influence of hemodynamics on carotid artery disease. However, the design of in vitro blood flow studies involves many steps and selection of imaging techniques, model materials, model design, and flow visualization parameters. Therefore, an overview of the possibilities and guidance for the design process is beneficial for researchers with less experience in flow studies.

METHODS

A systematic search to in vitro flow studies in carotid artery bifurcation models aiming at quantification and detailed flow visualization of blood flow dynamics results in inclusion of 42 articles.

RESULTS

Four categories of imaging techniques are distinguished: MRI, optical particle image velocimetry (PIV), ultrasound and miscellaneous techniques. Parameters for flow visualization are categorized into velocity, flow, shear-related, turbulent/disordered flow and other parameters. Model materials and design characteristics vary between study type.

CONCLUSIONS

A simplified three-step design process is proposed for better fitting and adequate match with the pertinent research question at hand and as guidance for less experienced flow study researchers. The three consecutive selection steps are: flow parameters, image modality, and model materials and designs. Model materials depend on the chosen imaging technique, whereas choice of flow parameters is independent from imaging technique and is therefore only determined by the goal of the study.

Comparing Morphology and Hemodynamics of Stable-versus-Growing and Grown Intracranial Aneurysms

BACKGROUND AND PURPOSE

Aneurysm growth has been related to higher rupture risk. A better understanding of the characteristics related to growth may assist in the treatment decisions of unruptured intracranial aneurysms. This study aimed to identify morphologic and hemodynamic characteristics associated with aneurysm growth and to determine whether these characteristics deviate further from those of stable aneurysms after growth.

MATERIALS AND METHODS

We included 81 stable and 56 growing aneurysms. 3D vascular models were segmented on CTA, MRA, or 3D rotational angiographic images. With these models, we performed computational fluid dynamics simulations. Morphologic (size, size ratios, and shape) and hemodynamic (inflow, vorticity, shear stress, oscillatory shear index, flow instability) characteristics were automatically calculated. We compared the characteristics between aneurysms that were stable and those that had grown at baseline and final imaging. The significance level after Bonferroni correction was P < .002.

RESULTS

At baseline, no significant differences between aneurysms that were stable and those that had grown were detected (P > .002). Significant differences between aneurysms that were stable and those that had grown were seen at the final imaging for shear rate, aneurysm velocity, vorticity, and mean wall shear stress (P < .002). The latter was 11.5 (interquartile range, 5.4-18.8 dyne/cm²) compared with 17.5 (interquartile range, 11.2-29.9 dyne/cm²) in stable aneurysms (P = .001). Additionally, a trend toward lower area weighted average Gaussian curvature in aneurysms that had grown was observed with a median of 6.0 (interquartile range, 3.2-10.7 cm^-2) compared with 10.4 (interquartile range, 5.0-21.2 cm^-2) in stable aneurysms (P = .004).

CONCLUSIONS

Morphologic and hemodynamic characteristics at baseline were not associated with aneurysm growth in our population. After growth, almost all indices increase toward values associated with higher rupture risks. Therefore, we stress the importance of longitudinal imaging and repeat risk assessment in unruptured aneurysms.

Performance evaluation of Cerenkov luminescence imaging: a comparison of 68Ga with 18F

BACKGROUND

Cerenkov Luminescence Imaging (CLI) is an emerging technology for intraoperative margin assessment. Previous research only evaluated radionuclide 18-Fluorine (¹⁸F); however, for future applications in prostate cancer, 68-Gallium (⁶⁸Ga) seems more suitable, given its higher positron energy. Theoretical calculations predict that ⁶⁸Ga should offer a higher signal-to-noise ratio than ¹⁸F; this is the first experimental confirmation. The aim of this study is to investigate the technical performance of CLI by comparing ⁶⁸Ga to ¹⁸F.

RESULTS

The linearity of the system, detection limit, spatial resolution, and uniformity were determined with the LightPath imaging system. All experiments were conducted with clinically relevant activity levels in vitro, using dedicated phantoms. For both radionuclides, a linear relationship between the activity concentration and detected light yield was observed (R² = 0.99). ⁶⁸Ga showed approximately 22 times more detectable Cerenkov signal compared to ¹⁸F. The detectable activity concentration after a 120 s exposure time and 2 × 2 binning of ¹⁸F was 23.7 kBq/mL and 1.2 kBq/mL for ⁶⁸Ga. The spatial resolution was 1.31 mm for ¹⁸F and 1.40 mm for ⁶⁸Ga. The coefficient of variance of the uniformity phantom was 0.07 for the central field of view.

CONCLUSION

⁶⁸Ga was superior over ¹⁸F in terms of light yield and minimal detection limit. However, as could be expected, the resolution was 0.1 mm less for ⁶⁸Ga. Given the clinical constraints of an acquisition time less than 120 s and a spatial resolution < 2 mm, CLI for intraoperative margin assessment using ⁶⁸Ga could be feasible.

Quantitative 3D measurements of tibial plateau fractures

Fracture gap and step-off measurements on 2DCT-slices probably underestimate the complex multi-directional features of tibial plateau fractures. Our aim was to develop a quantitative 3D-CT (Q3DCT) fracture analysis of these injuries. CT-based 3D models were created for 10 patients with a tibial plateau fracture. Several 3D measures (gap area, articular surface involvement, 3D displacement) were developed and tested. Gaps and step-offs were measured in 2D and 3D. All measurements were repeated by six observers and the reproducibility was determined by intra-class correlation coefficients. Q3DCT measurements demonstrated a median gap of 5.3 mm, step-off of 5.2 mm, gap area of 235 mm², articular surface involvement of 33% and 3D displacement of 6.1 mm. The inter-rater reliability was higher in the Q3DCT than in the 2DCT measurements for both the gap (0.96 vs. 0.81) and step-off (0.63 vs. 0.32). Q3DCT measurements showed excellent reliability (ICC of 0.94 for gap area, 1 for articular surface involvement and 0.99 for 3D displacement). Q3DCT fracture analysis of tibial plateau fractures is feasible and shows excellent reliability. 3D measurements could be used together with the current classification systems to quantify the true extent of these complex multi-directional fractures in a standardized way.

Deep learning enables automatic quantitative assessment of puborectalis muscle and urogenital hiatus in plane of minimal hiatal dimensions

OBJECTIVES

To measure the length, width and area of the urogenital hiatus (UH), and the length and mean echogenicity (MEP) of the puborectalis muscle (PRM), automatically and observer-independently, in the plane of minimal hiatal dimensions on transperineal ultrasound (TPUS) images, by automatic segmentation of the UH and the PRM using deep learning.

METHODS

In 1318 three- and four-dimensional (3D/4D) TPUS volume datasets from 253 nulliparae at 12 and 36 weeks' gestation, two-dimensional (2D) images in the plane of minimal hiatal dimensions with the PRM at rest, on maximum contraction and on maximum Valsalva maneuver, were obtained manually and the UH and PRM were segmented manually. In total, 713 of the images were used to train a convolutional neural network (CNN) to segment automatically the UH and PRM in the plane of minimal hiatal dimensions. In the remainder of the dataset (test set 1 (TS1); 601 images, four having been excluded), the performance of the CNN was evaluated by comparing automatic and manual segmentations. The performance of the CNN was also tested on 117 images from an independent dataset (test set 2 (TS2); two images having been excluded) from 40 nulliparae at 12 weeks' gestation, which were acquired and segmented manually by a different observer. The success of automatic segmentation was assessed visually. Based on the CNN segmentations, the following clinically relevant parameters were measured: the length, width and area of the UH, the length of the PRM and MEP. The overlap (Dice similarity index (DSI)) and surface distance (mean absolute distance (MAD) and Hausdorff distance (HDD)) between manual and CNN segmentations were measured to investigate their similarity. For the measured clinically relevant parameters, the intraclass correlation coefficients (ICCs) between manual and CNN results were determined.

RESULTS

Fully automatic CNN segmentation was successful in 99.0% and 93.2% of images in TS1 and TS2, respectively. DSI, MAD and HDD showed good overlap and distance between manual and CNN segmentations in both test sets. This was reflected in the respective ICC values in TS1 and TS2 for the length (0.96 and 0.95), width (0.77 and 0.87) and area (0.96 and 0.91) of the UH, the length of the PRM (0.87 and 0.73) and MEP (0.95 and 0.97), which showed good to very good agreement.

CONCLUSION

Deep learning can be used to segment automatically and reliably the PRM and UH on 2D ultrasound images of the nulliparous pelvic floor in the plane of minimal hiatal dimensions. These segmentations can be used to measure reliably UH dimensions as well as PRM length and MEP. © 2018 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of the International Society of Ultrasound in Obstetrics and Gynecology.

Impact of regadenoson-induced myocardial creep on dynamic Rubidium-82 PET myocardial blood flow quantification

BACKGROUND

Repositioning of the heart during myocardial perfusion imaging (MPI) using Rubidium-82 (Rb-82) PET may occur when using regadenoson. Our aim was to determine the prevalence and the effect of correcting for this myocardial creep on myocardial blood flow (MBF) quantification.

METHODS

We retrospectively included 119 consecutive patients who underwent dynamic rest- and regadenoson-induced stress MPI using Rb-82 PET. The presence of myocardial creep was visually assessed in the dynamic stress PET series by identifying differences between the automatically drawn myocardium contour and the activity. Uncorrected and corrected stress MBFs were compared for the three vascular territories (LAD, LCX, and RCA) and for the whole myocardium.

RESULTS

Myocardial creep was observed in 52% of the patients during stress. Mean MBF values decreased after correction in the RCA from 4.0 to 2.7 mL/min/g (P  < 0.001), in the whole myocardium from 2.7 to 2.6 mL/min/g (P  = 0.01), and increased in the LAD from 2.5 to 2.6 mL/min/g (P  = 0.03) and remained comparable in the LCX (P  = 0.3).

CONCLUSIONS

Myocardial creep is a frequent phenomenon when performing regadenoson-induced stress Rb-82 PET and has a significant impact on MBF values, especially in the RCA territory. As this may hamper diagnostic accuracy, myocardial creep correction seems necessary for reliable quantification.

Correction to: No need for frame-wise attenuation correction in dynamic Rubidium-82 PET for myocardial blood flow quantification

Due to the typesetter not carrying out the author's corrections at proof stage, there are two errors in the published article: where "mL × min × g" appears, it should be "mL/min/g". One error is in the Figure 3 caption, and one error is in the second sentence under the heading "MBF Quantification". The original article has been corrected.

No need for frame-wise attenuation correction in dynamic Rubidium-82 PET for myocardial blood flow quantification

BACKGROUND

Regadenoson-induced stress causes a repositioning of the heart, myocardial creep, in half of the patients undergoing Rubidium-82 (Rb-82) positron emission tomography (PET). As a result, misalignment of dynamic PET and computer tomography (CT) may occur, possibly affecting CT-based attenuation correction (AC) and thereby PET-based myocardial blood flow (MBF) quantification. Our aim was to determine the need for frame-wise PET-CT AC to obtain reliable MBF measurements.

METHODS

31 Out of 64 consecutive patients had myocardial creep during regadenoson-induced stress Rb-82 PET-CT and were included. Prior to PET image reconstruction, we applied two AC methods; single PET-CT alignment and frame-wise alignment in which PET time-frames with myocardial creep were individually co-registered with CT. The PET-CT misalignment was then quantified and MBFs for the three vascular territories and whole myocardium were calculated and compared between both methods.

RESULTS

The magnitude of misalignment due to myocardial creep was 13.8 ± 4.5 mm in caudal-cranial direction, 1.8 ± 2.1 mm in medial-lateral and 2.5 ± 1.8 mm in anterior-posterior direction. Frame-wise PET-CT registration did not result in different MBF measurements (P ≥ .07) and the magnitude of misalignment and MBF differences did not correlate (P ≥ .58).

CONCLUSION

There is no need for frame-wise AC in dynamic Rb-82 PET for MBF quantification. Single alignment seems sufficient in patients with myocardial creep.

How to detect and correct myocardial creep in myocardial perfusion imaging using Rubidium-82 PET?

Reliability of myocardial blood flow (MBF) quantification in myocardial perfusion imaging (MPI) using PET can majorly be affected by the occurrence of myocardial creep when using pharmacologically induced stress. In this paper, we provide instructions on how to detect and correct for myocardial creep. For example, in each time frame of the PET images the myocardium contour and the observed activity have to be compared to check for misalignments. In addition, we provide an overview of the functionality of commonly used software packages to perform this quality control step as not all software packages currently provide this functionality. Furthermore, important clinical considerations to obtain accurate MBF measurements are given.

Impact of Intracranial Aneurysm Morphology and Rupture Status on the Particle Residence Time

BACKGROUND AND PURPOSE

Aneurysm hemodynamics play an important role in aneurysm growth and subsequent rupture. Within the available hemodynamic characteristics, particle residence time (PRT) is relatively unexplored. However, some studies have shown that PRT is related to thrombus formation and inflammation. The goal of this study is to evaluate the association between PRT and aneurysm rupture and morphology.

METHODS

We determined the PRT for 113 aneurysms (61 unruptured, 53 ruptured) based on computational fluid dynamic models. Virtual particles were injected into the parent vessel and followed during multiple cardiac cycles. PRT was defined as the time needed for 99% of the particles that entered an aneurysm to leave the aneurysm. Subsequently, we evaluated the association between PRT, rupture, and morphology (aneurysm type, presence of blebs, or multiple lobulations).

RESULTS

PRT showed no significant difference between unruptured (1.1 seconds interquartile range [IQR .39-2.0 seconds]) and ruptured aneurysms (1.2 seconds [IQR .47-2.3 seconds]). PRT was influenced by aneurysm morphology. Longer PRTs were seen in bifurcation aneurysms (1.3 seconds [IQR .54-2.4 seconds], P = .01) and aneurysms with blebs or multiple lobulations (1.92 seconds [IQR .94-2.8 seconds], P < .001). Four of five partially thrombosed aneurysms had a long residence time (>1.9 seconds).

CONCLUSIONS

Our study shows an influence of aneurysm morphology on PRT. Nevertheless, it suggests that PRT cannot be used to differentiate unruptured and ruptured aneurysms.

Metal artifact reduction techniques in musculoskeletal CT-imaging

It is known that metal artifacts can be reduced by modifying standard acquisition and reconstruction, by modifying projection data and/or image data and by using virtual monochromatic imaging extracted from dual-energy CT. In this review we focus on the origin of metal artifacts, technical background of commercially available metal artifact reduction (MAR) algorithms and the value of dual-energy CT and MAR software for different metal hardware in current clinical practice. Virtual monochromatic imaging reduces beam-hardening artifacts, where metal artifact reduction software effectively reduces artifacts caused by extensive photon-starvation. Both techniques have their advantages and disadvantages, and the combination of both techniques is often but not always the best solution regarding metal artifact reduction. Advances in prosthetic imaging are reinforced by advances in prosthetic design. Providing implant specific information prior to scanning is important in order to adjust the metal artifact reduction approach, minimize artifacts and optimize image quality and diagnostic value of CT.

Automatic segmentation of puborectalis muscle on three-dimensional transperineal ultrasound

OBJECTIVES

The introduction of three-dimensional (3D) analysis of the puborectalis muscle (PRM) for diagnostic purposes into daily practice is hindered by the need for appropriate training of observers. Automatic segmentation of the PRM on 3D transperineal ultrasound may aid its integration into clinical practice. The aims of this study were to present and assess a protocol for manual 3D segmentation of the PRM on 3D transperineal ultrasound, and to use this for training of automatic 3D segmentation method of the PRM.

METHODS

The data used in this study were derived from 3D transperineal ultrasound sequences of the pelvic floor acquired at 12 weeks' gestation from nulliparous women with a singleton pregnancy. A manual 3D segmentation protocol was developed for the PRM based on a validated two-dimensional segmentation protocol. For automatic segmentation, active appearance models of the PRM were developed, trained using manual segmentation data from 50 women. The performances of both manual and automatic segmentation were analyzed by measuring the overlap and distance between the segmentations. Intraclass correlation coefficients (ICCs) and their 95% CIs were determined for mean echogenicity and volume of the puborectalis muscle, in order to assess inter- and intraobserver reliabilities of the manual method using data from 20 women, as well as to compare the manual and automatic methods.

RESULTS

Interobserver reliabilities for mean echogenicity and volume were very good for manual segmentation (ICCs 0.987 and 0.910, respectively), as were intraobserver reliabilities (ICCs 0.991 and 0.877, respectively). ICCs for mean echogenicity and volume were very good and good, respectively, for the comparison of manual vs automatic segmentation (0.968 and 0.626, respectively). The overlap and distance results for manual segmentation were as expected, showing an average mismatch of only 2-3 pixels and reasonable overlap. Based on overlap and distance, five mismatches were detected for automatic segmentation, resulting in an automatic segmentation success rate of 90%.

CONCLUSIONS

This study presents a reliable manual segmentation protocol and automatic 3D segmentation method for the PRM, which will facilitate future investigation of the PRM, allowing for the reliable measurement of potentially clinically valuable parameters such as mean echogenicity. © 2017 The Authors. Ultrasound in Obstetrics & Gynecology Published by John Wiley & Sons Ltd on behalf of the International Society of Ultrasound in Obstetrics and Gynecology.

Value of Quantitative Collateral Scoring on CT Angiography in Patients with Acute Ischemic Stroke

BACKGROUND AND PURPOSE

Many studies have emphasized the relevance of collateral flow in patients presenting with acute ischemic stroke. Our aim was to evaluate the relationship of the quantitative collateral score on baseline CTA with the outcome of patients with acute ischemic stroke and test whether the timing of the CTA acquisition influences this relationship.

MATERIALS AND METHODS

From the Multicenter Randomized Clinical Trial of Endovascular Treatment of Acute Ischemic Stroke in the Netherlands (MR CLEAN) data base, all baseline thin-slice CTA images of patients with acute ischemic stroke with intracranial large-vessel occlusion were retrospectively collected. The quantitative collateral score was calculated as the ratio of the vascular appearance of both hemispheres and was compared with the visual collateral score. Primary outcomes were 90-day mRS score and follow-up infarct volume. The relation with outcome and the association with treatment effect were estimated. The influence of the CTA acquisition phase on the relation of collateral scores with outcome was determined.

RESULTS

A total of 442 patients were included. The quantitative collateral score strongly correlated with the visual collateral score (ρ = 0.75) and was an independent predictor of mRS (adjusted odds ratio = 0.81; 95% CI, .77-.86) and follow-up infarct volume (exponent β = 0.88; P < .001) per 10% increase. The quantitative collateral score showed areas under the curve of 0.71 and 0.69 for predicting functional independence (mRS 0-2) and follow-up infarct volume of >90 mL, respectively. We found significant interaction of the quantitative collateral score with the endovascular therapy effect in unadjusted analysis on the full ordinal mRS scale (P = .048) and on functional independence (P = .049). Modification of the quantitative collateral score by acquisition phase on outcome was significant (mRS: P = .004; follow-up infarct volume: P < .001) in adjusted analysis.

CONCLUSIONS

Automated quantitative collateral scoring in patients with acute ischemic stroke is a reliable and user-independent measure of the collateral capacity on baseline CTA and has the potential to augment the triage of patients with acute stroke for endovascular therapy.

Aneurysmal Parent Artery-Specific Inflow Conditions for Complete and Incomplete Circle of Willis Configurations

BACKGROUND AND PURPOSE

Hemodynamics are thought to play a role in intracranial aneurysm growth and rupture. Computational fluid dynamics is frequently performed to assess intra-aneurysmal hemodynamics, using generalized flow waveforms of healthy volunteers as inflow boundary conditions. The purpose of this study was to assess differences in inflow conditions for different aneurysmal parent artery locations and variations of circle of Willis configurations.

MATERIALS AND METHODS

In a series of 96 patients with 103 aneurysms, velocity measurements were acquired using 2D phase-contrast MR imaging perpendicular to the aneurysmal parent arteries in the circle of Willis. Circle of Willis configurations were inspected for variations using multiple overlapping thin-slab-acquisition MRAs. Flow rates, velocity magnitudes, and pulsatility indices were calculated for each parent artery location in subgroups of complete and incomplete circle of Willis configurations.

RESULTS

Flow rates, velocity magnitudes, and pulsatility indices were significantly different among aneurysmal parent arteries. Incomplete circle of Willis configurations were observed in 24% of the cases. Significantly lower basilar artery flow rates were observed in configurations with hypoplastic P1 segments. Significantly higher A1 flow rates were observed in configurations with a hypoplastic contralateral A1 segment.

CONCLUSIONS

Inflow conditions vary substantially between aneurysmal parent arteries and circle of Willis configurations. We have created a collection of parent artery-specific inflow conditions tailored to the patient-specific circle of Willis configuration that can be used in future computational fluid dynamics studies analyzing intra-aneurysmal hemodynamics.

Low-dose CT imaging of a total hip arthroplasty phantom using model-based iterative reconstruction and orthopedic metal artifact reduction

OBJECTIVE

To compare quantitative measures of image quality, in terms of CT number accuracy, noise, signal-to-noise-ratios (SNRs), and contrast-to-noise ratios (CNRs), at different dose levels with filtered-back-projection (FBP), iterative reconstruction (IR), and model-based iterative reconstruction (MBIR) alone and in combination with orthopedic metal artifact reduction (O-MAR) in a total hip arthroplasty (THA) phantom.

MATERIALS AND METHODS

Scans were acquired from high- to low-dose (CTDI_vol: 40.0, 32.0, 24.0, 16.0, 8.0, and 4.0 mGy) at 120- and 140- kVp. Images were reconstructed using FBP, IR (iDose⁴ level 2, 4, and 6) and MBIR (IMR, level 1, 2, and 3) with and without O-MAR. CT number accuracy in Hounsfield Units (HU), noise or standard deviation, SNRs, and CNRs were analyzed.

RESULTS

The IMR technique showed lower noise levels (p < 0.01), higher SNRs (p < 0.001) and CNRs (p < 0.001) compared with FBP and iDose⁴ in all acquisitions from high- to low-dose with constant CT numbers. O-MAR reduced noise (p < 0.01) and improved SNRs (p < 0.01) and CNRs (p < 0.001) while improving CT number accuracy only at a low dose. At the low dose of 4.0 mGy, IMR level 1, 2, and 3 showed 83%, 89%, and 95% lower noise values, a factor 6.0, 9.2, and 17.9 higher SNRs, and 5.7, 8.8, and 18.2 higher CNRs compared with FBP respectively.

CONCLUSIONS

Based on quantitative analysis of CT number accuracy, noise values, SNRs, and CNRs, we conclude that the combined use of IMR and O-MAR enables a reduction in radiation dose of 83% compared with FBP and iDose⁴ in the CT imaging of a THA phantom.

Value of attenuation correction in stress-only myocardial perfusion imaging using CZT-SPECT

BACKGROUND

Attenuation correction (AC) improves the diagnostic outcome of stress-only myocardial perfusion imaging (MPI) using conventional SPECT. Our aim was to determine the value of AC using a cadmium zinc telluride-based (CZT)-SPECT camera.

METHODS AND RESULTS

We retrospectively included 107 consecutive patients who underwent stress-optional rest MPI CZT-SPECT/CT. Next, we created three types of images for each patient; (1) only displaying reconstructed data without the CT-based AC (NC), (2) only displaying AC, and (3) with both NC and AC (NC + AC). Next, two experienced physicians visually interpreted these 321 randomized images as normal, equivocal, or abnormal. Image outcome was compared with all hard events over a mean follow-up time of 47.7 ± 9.8 months. The percentage of images interpreted as normal increased from 45% using the NC images to 72% using AC and to 67% using NC + AC images (P < .001). Hard event hazard ratios for images interpreted as normal were not different between using NC and AC (1.01, P = .99), or NC and NC + AC images (0.97, P = .97).

CONCLUSIONS

AC lowers the need for additional rest imaging in stress-first MPI using CZT-SPECT, while long-term patient outcome remained identical. Use of AC reduces the need for additional rest imaging, decreasing the mean effective dose by up to 1.2 mSv.

Feasibility of a low concentration test bolus in CT angiography

AIM

To investigate the feasibility of using a low-concentration test bolus in abdominal aorta computed tomography (CT) angiography (CTA).

MATERIALS AND METHODS

In 10 patients referred for CTA of the abdominal aorta with a body mass index (BMI) ≤28 kg/m², a standard test bolus of 10 ml contrast medium (CM; 350 mg iodine/ml) was compared with a low-concentration test bolus (5 ml CM; 350 mg iodine/ml; 1:1 diluted with saline) in terms of time to peak enhancement (tPE) and peak enhancement (PE).

RESULTS

No significant differences were found between the standard and low-concentration test bolus in terms of tPE and PE.

CONCLUSIONS

A low-concentration test bolus (5 ml, 1:1 diluted with saline) is feasible in patients with a BMI ≤28 kg/m².

Skeletal muscle mass and quality as risk factors for postoperative outcome after open colon resection for cancer

BACKGROUND

The prevalence of colorectal cancer in the elderly is increasing and, therefore, surgical interventions with a risk of potential complications are more frequently performed. This study investigated the role of low skeletal muscle mass (sarcopenia), muscle quality, and the sarcopenic obesity as prognostic factors for postoperative complications and survival in patients with resectable colon cancer.

METHODS

We conducted a retrospective chart review of 91 consecutive patients who underwent an elective open colon resection for cancer with primary anastomosis between 2011 and 2013. Skeletal muscle mass was measured as total psoas area (TPA) and total abdominal muscle area (TAMA) at three anatomical levels on the preoperative CT scan. Skeletal muscle quality was measured using corresponding mean Hounsfield units (HU) for TAMA. Their relation with complications (none vs one or more), severe complications, and survival was analyzed.

RESULTS

The study included 91 patients with a mean age of 71.2 ± 9.7 years. Complications were noted in 55 patients (60 %), of which 15 (16.4 %) were severe. Lower HU for TAMA, as an indicator for impaired skeletal muscle quality, was an independent risk factor for one or more complications (all P ≤ 0.002), while sarcopenic obesity (TPA) was an independent risk factor for severe complications (all P ≤ 0.008). Sarcopenia was an independent predictor of worse overall survival (HR 8.54; 95 % confidence interval (CI) 1.07-68.32).

CONCLUSION

Skeletal muscle quality is a predictor for overall complications, whereas sarcopenic obesity is a predictor for severe postoperative complications after open colon resection for cancer. Sarcopenia on itself is a predictor for worse overall survival.

Topographic distribution of cerebral infarct probability in patients with acute ischemic stroke: mapping of intra-arterial treatment effect

BACKGROUND

Since proof emerged that IA treatment (IAT) is beneficial for patients with acute ischemic stroke, it has become the standard method of care. Despite these positive results, recovery to functional independence is established in only about one-third of treated patients. The effect of IAT is commonly assessed by functional outcome, whereas its effect on brain tissue salvage is considered a secondary outcome measure (at most). Because patient and treatment selection needs to be improved, understanding the treatment effect on brain tissue salvage is of utmost importance.

OBJECTIVE

To introduce infarct probability maps to estimate the location and extent of tissue damage based on patient baseline characteristics and treatment type.

METHODS

Cerebral infarct probability maps were created by combining automatically segmented infarct distributions using follow-up CT images of 281 patients from the MR CLEAN trial. Comparison of infarct probability maps allows visualization and quantification of probable treatment effects. Treatment impact was calculated for 10 Alberta Stroke Program Early CT Score (ASPECTS) and 27 anatomical regions.

RESULTS

The insular cortex had the highest infarct probability in both control and IAT populations (47.2% and 42.6%, respectively). Comparison showed significant lower infarct probability in 4 ASPECTS and 17 anatomical regions in favor of IAT. Most salvaged tissue was found within the ASPECTS M2 region, which was 8.5% less likely to infarct.

CONCLUSIONS

Probability maps intuitively visualize the topographic distribution of infarct probability due to treatment, which makes it a promising tool for estimating the effect of treatment.

A non-invasive cardiac output measurement as an alternative to the test bolus technique during CT angiography

AIM

To investigate the association between a non-invasive cardiac output (CO) measurement and the scan delay, as derived from a test bolus injection protocol. The secondary objective was to determine which factors affect the relationship between the CO and scan delay.

MATERIALS AND METHODS

Fifty-five patients referred for a contrast-enhanced (thorax-)abdomen CT examination were included in this feasibility study. A test bolus examination was performed prior to the abdominal CT. During the test bolus injection, the CO of the patient was measured using a non-invasive finger-cuff measurement. Associations were analysed using linear regression analyses. Age, gender, height, weight, and blood pressure were included as potential confounders.

RESULTS

Linear regression analysis showed a negative and significant association between CO and delay. The regression formula was as follows: scan delay (seconds) = 26.8-1.6 CO (l/min), with a 95% CI between -2.3 and -1.0 (p<0.001). Weight appeared to be a confounder in this relation, and gender and blood pressure were effect modifiers. There was no interaction between scan delay and age, height and weight.

CONCLUSIONS

There is a negative and significant association between the non-invasive CO measurement and the CT scan delay; however, to validate these findings a larger cohort study is needed to investigate whether the non-invasively determined scan delay is as accurate as the use of a test bolus.

A practical approach for a patient-tailored dose protocol in coronary CT angiography using prospective ECG triggering

To derive and validate a practical patient-specific dose protocol to obtain an image quality, expressed by the image noise, independent of patients' size and a better radiation dose justification in coronary CT angiography (CCTA) using prospective ECG triggering. 43 patients underwent clinically indicated CCTA. The image noise, defined as the standard deviation of pixel attenuation values in a homogeneous region in the liver, was determined in all scans. Subsequently, this noise was normalized to the radiation exposure. Next, three patient-specific parameters, body weight, body mass index and mass per length (MPL), were tested for the best correlation with normalized image noise. From these data, a new dose protocol to provide a less variable image noise was derived and subsequently validated in 84 new patients. The normalized image noise increased for heavier patients for all patients' specific parameters (p < 0.001). MPL correlated best with the normalized image noise and was selected for dose protocol optimization. This new protocol resulted in image noise levels independent of patients' MPL (p = 0.28). A practical method to obtain CCTA images with noise levels independent of patients' MPL was derived and validated. It results in a less variable image quality and better radiation exposure justification and can also be used for CT scanners from other vendors.

Development and validation of a patient-tailored dose regime in myocardial perfusion imaging using conventional SPECT

BACKGROUND

The decreasing image quality in heavier patients can be compensated by administration of a patient-specific dose in myocardial perfusion imaging (MPI) using a cadmium zinc telluride-based SPECT camera. Our aim was to determine if the same can be achieved when using a conventional SPECT camera.

METHODS

148 patients underwent SPECT stress MPI using a fixed Tc-99m tetrofosmin tracer dose. Measured photon counts were normalized to administered tracer dose and scan time and were correlated with body weight, body mass index, and mass per length to find the best predicting parameter. From these data, a protocol to provide constant image quality was derived, and subsequently validated in 125 new patients.

RESULTS

Body weight was found to be the best predicting parameter for image quality and was used to derive a new dose formula; A admin (MBq) = 223·body weight (kg)(0.65)/T scan (min). The measured photon counts decreased in heavier patients when using a fixed dose (P < .01) but this was no longer observed after applying a body-weight-dependent protocol (P = .20).

CONCLUSIONS

Application of a patient-specific protocol resulted in an image quality less depending on patient's weight. The results are most likely independent of the type of SPECT camera used, and, hence, adoption of patient-specific dose and scan time protocols is recommended.

Dentatorubrothalamic tract localization with postmortem MR diffusion tractography compared to histological 3D reconstruction

Diffusion-weighted imaging (DWI) tractography is a technique with great potential to characterize the in vivo anatomical position and integrity of white matter tracts. Tractography, however, remains an estimation of white matter tracts, and false-positive and false-negative rates are not available. The goal of the present study was to compare postmortem tractography of the dentatorubrothalamic tract (DRTT) by its 3D histological reconstruction, to estimate the reliability of the tractography algorithm in this specific tract. Recent studies have shown that the cerebellum is involved in cognitive, language and emotional functions besides its role in motor control. However, the exact working mechanism of the cerebellum is still to be elucidated. As the DRTT is the main output tract it is of special interest for the neuroscience and clinical community. A postmortem human brain specimen was scanned on a 7T MRI scanner using a diffusion-weighted steady-state free precession sequence. Tractography was performed with PROBTRACKX. The specimen was subsequently serially sectioned and stained for myelin using a modified Heidenhain–Woelke staining. Image registration permitted the 3D reconstruction of the histological sections and comparison with MRI. The spatial concordance between the two modalities was evaluated using ROC analysis and a similarity index (SI). ROC curves showed a high sensitivity and specificity in general. Highest measures were observed in the superior cerebellar peduncle with an SI of 0.72. Less overlap was found in the decussation of the DRTT at the level of the mesencephalon. The study demonstrates high spatial accuracy of postmortem probabilistic tractography of the DRTT when compared to a 3D histological reconstruction. This gives hopeful prospect for studying structure–function correlations in patients with cerebellar disorders using tractography of the DRTT.

Hemodynamic Differences in Intracranial Aneurysms before and after Rupture

BACKGROUND AND PURPOSE

Rupture risk of intracranial aneurysms may depend on hemodynamic characteristics. This has been assessed by comparing hemodynamic data of ruptured and unruptured aneurysms. However, aneurysm geometry may change before, during, or just after rupture; this difference causes potential changes in hemodynamics. We assessed changes in hemodynamics in a series of intracranial aneurysms, by using 3D imaging before and after rupture.

MATERIALS AND METHODS

For 9 aneurysms in 9 patients, we used MRA, CTA, and 3D rotational angiography before and after rupture to generate geometric models of the aneurysm and perianeurysmal vasculature. Intra-aneurysmal hemodynamics were simulated by using computational fluid dynamics. Two neuroradiologists qualitatively assessed flow complexity, flow stability, inflow concentration, and flow impingement in consensus, by using flow-velocity streamlines and wall shear stress distributions.

RESULTS

Hemodynamics changed in 6 of the 9 aneurysms. The median time between imaging before and after rupture was 678 days (range, 14-1461 days) in these 6 cases, compared with 151 days (range, 34-183 days) in the 3 cases with unaltered hemodynamics. Changes were observed for flow complexity (n = 3), flow stability (n = 3), inflow concentration (n = 2), and region of flow impingement (n = 3). These changes were in all instances associated with aneurysm displacement due to rupture-related hematomas, growth, or newly formed lobulations.

CONCLUSIONS

Hemodynamic characteristics of intracranial aneurysms can be altered by geometric changes before, during, or just after rupture. Associations of hemodynamic characteristics with aneurysm rupture obtained from case-control studies comparing ruptured with unruptured aneurysms should therefore be interpreted with caution.

Computation of blood flow through collateral circulation of the superficial femoral artery

OBJECTIVE

Obliteration of collaterals during (endo)vascular treatment of peripheral arterial occlusive disease is considered detrimental. We use a model to calculate maximum collateral bed flow of the superficial femoral artery in order to provide insight in their hemodynamic relevance.

METHOD

A computational model was developed using digital subtraction angiographies in combination with Poiseuille's equation and Ohm's law. Lesions were divided into short and long (<15 cm and ≥15 cm, respectively) and into stenosis and occlusions. Data are presented in relation to the calculated maximum healthy superficial femoral artery flow.

RESULTS

Stenotic lesions are longer than occlusive lesions (P < 0.05) and occlusions had more and larger collaterals (P < 0.05). In all four study groups the collateral flow significantly increased the total flow (P < 0.05). The maximum collateral system flow in the stenosis and occlusion groups was 5.1% and 20.8% of healthy superficial femoral artery flow, respectively (P < 0.05), and there were no significant differences between short and long lesions (11.2% and 6.7% of healthy superficial femoral artery flow, respectively).

CONCLUSION

The maximum collateral system flow of the superficial femoral artery is only a fraction, with a maximum of one fifth, of healthy superficial femoral artery flow. Effects of collateral vessel occlusion during (endo)vascular treatment may therefore be without detrimental consequences.

Development and validation of a patient-tailored dose regime in myocardial perfusion imaging using CZT-SPECT

BACKGROUND

Guidelines for SPECT myocardial perfusion imaging (MPI) traditionally recommend a fixed tracer dose. Yet, clinical practice shows degraded image quality in heavier patients. The aim was to optimize and validate the tracer dose and scan time to obtain a constant image quality less dependent on patients' physical characteristics.

METHODS

125 patients underwent Cadmium Zinc Telluride (CZT)-SPECT stress MPI using a fixed Tc-99m-tetrofosmin tracer dose. Image quality was scored by three physicians on a 4-point grading scale and related to the number of photon counts normalized to tracer dose and scan time. Counts were correlated with various patient-specific parameters dealing with patient size and weight to find the best predicting parameter. From these data, a formula to provide constant image quality was derived, and subsequently tested in 92 new patients.

RESULTS

Degradation in image quality and photon counts was observed for heavier patients for all patients' specific parameters (P < .01). We found body weight to be the best-predicting parameter for image quality and derived a new dose formula. After applying this new body weight-depended tracer dose and scan time in a new group, image quality was found to be constant (P > .19) in all patients.

CONCLUSIONS

Also in CZT SPECT image quality decreases with weight. The use of a tracer dose and scan time that depends linearly on patient's body weight corrected for the varying image quality in CZT-SPECT MPI. This leads to better radiation exposure justification.

Preliminary results using a newly developed projection method to visualize vascular anatomy prior to DIEP flap breast reconstruction

INTRODUCTION

In a deep inferior epigastric perforator (DIEP) flap breast reconstruction, computed tomography angiography (CTA) is currently considered as the gold standard in preoperative imaging for this procedure. Unidirectional Doppler ultrasound (US) is frequently used; however, this method does not distinguish the main axial vessels from perforator arteries at the height of the fascia, it has a limited penetration depth, and it cannot assess the branching patterns of the deep inferior arteries. A new method and system were developed, which consisted of a video projector preoperatively displaying the location and intramuscular course of the artery perforators and subcutaneous branching on the patient's abdomen.

METHOD

All patients (n=9) underwent a standard protocol: a preoperative CTA was performed and the DIEPs were localized using a unidirectional Doppler probe. In addition, a three-dimensional (3D) reconstruction of the perforator locations based on CTA was projected on the abdomen of the patients. All projected perforator locations were assessed using a unidirectional Doppler probe. The intraoperative results were collected for comparison.

RESULTS

A total of 88 locations were marked with the use of unidirectional Doppler and a total of 100 perforators were projected (p=0.38). In 98 out of 100 projected perforator locations, a Doppler signal was audible. The intraoperative results demonstrate that 19 out of 34 transplanted perforators were correctly identified with unidirectional Doppler (56.9%±31.4%), where the projection method properly revealed 29 locations (84.3%±25.8%) (p=0.030).

CONCLUSION

The projection method is not only capable of providing more information and identifying more perforators used for transplantation than unidirectional Doppler probing but also more accurate in pointing out the corresponding perforator found intraoperatively.

Automatic quantification of subarachnoid hemorrhage on noncontrast CT

BACKGROUND AND PURPOSE

Quantification of blood after SAH on initial NCCT is an important radiologic measure to predict patient outcome and guide treatment decisions. In current scales, hemorrhage volume and density are not accounted for. The purpose of this study was to develop and validate a fully automatic method for SAH volume and density quantification.

MATERIALS AND METHODS

The automatic method is based on a relative density increase due to the presence of blood from different brain structures in NCCT. The method incorporates density variation due to partial volume effect, beam-hardening, and patient-specific characteristics. For validation, automatic volume and density measurements were compared with manual delineation on NCCT images of 30 patients by 2 radiologists. The agreement with the manual reference was compared with interobserver agreement by using the intraclass correlation coefficient and Bland-Altman analysis for volume and density.

RESULTS

The automatic measurement successfully segmented the hemorrhage of all 30 patients and showed high correlation with the manual reference standard for hemorrhage volume (intraclass correlation coefficient = 0.98 [95% CI, 0.96-0.99]) and hemorrhage density (intraclass correlation coefficient = 0.80 [95% CI, 0.62-0.90]) compared with intraclass correlation coefficient = 0.97 (95% CI, 0.77-0.99) and 0.98 (95% CI, 0.89-0.99) for manual interobserver agreement. Mean SAH volume and density were, respectively, 39.3 ± 31.5 mL and 62.2 ± 5.9 Hounsfield units for automatic measurement versus 39.7 ± 32.8 mL and 61.4 ± 7.3 Hounsfield units for manual measurement. The accuracy of the automatic method was excellent, with limits of agreement of -12.9-12.1 mL and -7.6-9.2 Hounsfield units.

CONCLUSIONS

The automatic volume and density quantification is very accurate compared with manual assessment. As such, it has the potential to provide important determinants in clinical practice and research.

Flow prediction in cerebral aneurysms based on geometry reconstruction from 3D rotational angiography

We present an immersed boundary (IB) method for the simulation of steady blood flow inside a realistic cerebral aneurysm. We reconstruct a segment of the cerebrovascular system that contains an aneurysm, by using medical images obtained with three dimensional rotational angiography (3DRA). The main focus is on evaluating the sensitivity of flow predictions to the various steps of the vascular reconstruction process. Starting from the raw medical data, we analyze the fluid-mechanical consequences of the steps needed to generate the IB masking function for our simulations. We illustrate the IB method by applying it to a realistic aneurysm and investigate the role of (i) numerical resolution of the geometry; (ii) the selection of the specific vascular segment used in the simulations; and (iii) the influence of the smoothness of the periodic vessel extension to complete the computational model. Because of an unavoidable degree of uncertainty in the medical images, the geometry of the vessels and the aneurysm can be reconstructed only approximately. We also incorporate these slight uncertainties in the masking function by introducing inner and outer 'bounding' geometries and analyze the sensitivity of the flow predictions to these variations in the masking function. The numerical solutions computed in the inner and outer bounding geometries provide practical upper and lower bounds for basic flow properties, thus quantifying the reliability of the numerical solution, subject to uncertainties in the geometry of the flow domain.

Speed-of-sound compensated photoacoustic tomography for accurate imaging

PURPOSE

In most photoacoustic (PA) tomographic reconstructions, variations in speed-of-sound (SOS) of the subject are neglected under the assumption of acoustic homogeneity. Biological tissue with spatially heterogeneous SOS cannot be accurately reconstructed under this assumption. The authors present experimental and image reconstruction methods with which 2D SOS distributions can be accurately acquired and reconstructed, and with which the SOS map can be used subsequently to reconstruct highly accurate PA tomograms.

METHODS

The authors begin with a 2D iterative reconstruction approach in an ultrasound transmission tomography setting, which uses ray refracted paths instead of straight ray paths to recover accurate SOS images of the subject. Subsequently, they use the SOS distribution in a new 2D iterative PA reconstruction approach, where refraction of rays originating from PA sources is accounted for in accurately retrieving the distribution of these sources. Both the SOS reconstruction and SOS-compensated PA reconstruction methods utilize the Eikonal equation to model acoustic wavefront propagation. The equation is solved using a high accuracy fast marching method.

RESULTS

The authors validated the new reconstruction algorithms using numerical phantoms. For experiments they utilized the recently introduced PER-PACT method which can be used to simultaneously acquire SOS and PA data from subjects.

CONCLUSIONS

It is first confirmed that it is important to take SOS inhomogeneities into account in high resolution PA tomography. The iterative reconstruction algorithms, that model acoustic refractive effects, in reconstructing SOS distributions, and subsequently using these distributions to correct PA tomograms, yield artifact-free highly accurate images. The approach of using the hybrid measurement method and the new reconstruction algorithms is successful in substantially improving the quality of PA images with a minimization of blurring and artifacts.

Digital densitometric determination of relative coronary flow distributions

In clinical cardiology, stenosis in a coronary artery is measured on the basis of visual assessment. The reading of coronary arteriograms leads, however, to large inter- and intra-observer variability. Image analysis and computer assistance result in a more consistent assessment, but this approach is mainly based upon static geometric parameters, such as diameter reduction of a segment of the stenosed artery. A more functional, physiological measurement is thus desirable. This can be realised by measuring the difference between the normal coronary blood flow and the increased flow under hyperaemic conditions, yielding the so-called coronary flow reserve (CFR). In clinical practice, however, this method is difficult and time-consuming. A less demanding approach is reported, in which relative flow distributions are determined densitometrically from digital angiograms acquired under basal and hyperaemic conditions. The proposition is that, if the relative flow distribution in hyperaemic state differs from that during rest, the functional severity of a stenosis downstream from the bifurcation can be indicated. The new approach is validated by comparing the results of a theoretical model for steady flow with a flow phantom experiment for steady and pulsatile flow. The obtained flow ratios correlate very well, both in steady and pulsatile flow, with correlation coefficients exceeding 0.95.

Pharmacokinetic analysis of Gd-DTPA enhancement in dynamic three-dimensional MRI of breast lesions

The purpose of this study was to demonstrate that dynamic MRI covering both breasts can provide sensitivity for tumor detection as well as specificity and sensitivity for differentiation of tumor malignancy. Three-dimensional gradient echo scans were used covering both breasts. Before Gd-DTPA bolus injection, two scans were obtained with different flip angles, and after injection, a dynamic series followed. Thirty-two patients were scanned according to this protocol. From these scans. In addition to enhancement, the value of T1 before injection was obtained. This was used to estimate the concentration of Gd-DTPA as well as the pharmacokinetic parameters governing its time course. Signal enhancement in three-dimensional dynamic scanning was shown to be a sensitive basis for detection of tumors. In our series, all but two mammographically suspicious lesions did enhance, and in three cases, additional enhancing lesions were found, two of which were in the contralateral breast. The parameter most suited for classification of breast lesions into benign or malignant was shown to be the pharmacokinetically defined permeability k31, which, for that test, gave a sensitivity of 92% and a specificity of 70%. Our three-dimensional dynamic MRI data are sensitive for detection of mammographically occult breast tumors and specific for classification of these as benign or malignant.