Bilal H. Malik

SPIE Digital Library Proceedings

The ability to conduct ‘partial field of view’ scans in QT ultrasound transmission ultrasound is investigated. The standard tomographic data acquisition is typically conducted in a full 360 degree aperture, which may limit the possibility of real time intervention and/or patient positioning for medical imaging. Transmission ultrasound has many advantages over other imaging modalities such as, it does not emit ionizing radiation, does not require contrast agent, etc. A partial field of view data acquisition in this context is therefore attractive. Three scenarios are investigated: breast, whole body, and orthopedic imaging. A full suite of 180 views at 2 degree intervals and 192 mm in the vertical direction was collected from the QT ultrasound™ scanner in the orthopedic and whole body scenarios. The vertical extent of the breast image varied with breast size. Subsequent reconstructions were carried out with a subset of the views incorporated. The contiguous sector of missing angles varied from 8, 16, 32, 40, 60 and 92 degrees. The difference between the corresponding images was quantitatively and qualitatively analyzed and compared. It was found that a large lacuna (gap) of contiguous data did not significantly (clinically) degrade image quality, and the quantitative values, where relevant. The open acquisition scenario allows us to carry out medical intervention as well as potentially decrease patient anxiety. The quantitative nature of the degradation is noted and correlated with the missing sector angles for clinical scenarios, and the implications discussed.

Breast density is now recognized as one of the most important independent risk factors of breast cancer. Current means to assess breast density primarily utilize mammograms which represent a series of projection images, making it difficult to estimate the true volume of the fibroglandular tissue. We present 3D transmission ultrasound as a method to visualize and differentiate fibroglandular tissue within the breast and use an unsupervised learning-based method to quantitatively assess the respective breast density. The method includes initial separation of breast from the surrounding water bath followed by segmentation of the whole breast into fibroglandular tissue and fat using fuzzy C-mean (FCM) classification. We apply these methods to both tissue phantoms (in vitro) and clinical breast images (in vivo). In the case of tissue phantoms, the agreement between the theoretical (geometric density) and experimentally calculated values was better than 90%. For density calculation in a sample size of 50 cases, the results correlate well (Spearman r = 0.93, 95% CI: 0.88-0.96, p<0.0001) with an FDA-cleared breast density assessment software, VolparaDensity. We also discuss the advantage of using FCMbased tissue classification over threshold-based tissue segmentation within the paradigm of iterative image inversion/reconstruction and show that the former method is less sensitive to variation in assessment of breast density as a function of iteration count and thus, less dependent on convergence criteria. These results imply that breast density as assessed by 3D transmission ultra-sound can be of significant clinical utility and play an important role in breast cancer risk assessment.

Muscular Dystrophy (Duchenne) and osteoarthritis are important diseases requiring quantitative tissue measurement for accurate monitoring. MRI with Dixon Sequences, Nakagami statistics, elastography and radiography have been used in semi-quantitative modes to infer myopathy, articular cartilage damage, and exercise induced muscle damage. We establish the high resolution quantitative accuracy of transmission ultrasound imaging using both fresh and cadaver knee tissue. The use of fresh tissue obviates the possibility that cadaverous tissue has different speed of sound (SOS) values due to fixation. We show also that the fixation procedure changes the SOS values by about 0.1% to 0.4% fibroglandular tissue, fat and skin. The use of multiple transverse sections at varying distances from the tibiofemoral space ameliorates bias. Using a 6 mm diameter ROI at 20 successive levels, the SOS measured for the Vastus medialis was 1573 m/s with a 95% CI of +/-1.8 m/s. The average standard deviation (SD) for the ROI’s altogether was 25.9 m/s. The accepted SOS value for muscle from the IT’IS Foundation, Zurich, is 1588.4, SD = 21.6 m/s. Similar results for 6 mm diameter ROI’s in fat at successive transverse sections yields an average of 1438.7 m/s, the ROI SD’s averaged 20.5 m/s. The IT’IS values are 1440 m/s with SD 21.4 m/s. Cartilage gives similar agreement: literature value is 1660 m/s, and we measure 1655.4 m/s (SD 14.6) in 4 mm diameter ROI. We show regions that have no MR response yet are quantitatively imaged in 3D transmission ultrasound.

Encouraged by progress over the past 10 years in breast imaging, we have generalized 3D ultrasound transmission tomography (UST) to orthopaedic, whole body and clinical applications. We document quantitative breast density measurement, quantitative transmission tomography in the presence of bone and air, and tumor monitoring applications, indicating that 3D UST is a whole body imaging modality with clinical implications.

Purpose: Quantitative Transmission (QT) ultrasound has shown promise as a breast imaging modality. This study characterizes the performance of the latest generation ofQTultrasound scanners:QTScanner 2000.Methods: The scanner consists of a 2048‐element ultrasound receiver array for transmission imaging and three transceivers for reflection imaging. Custom fabricated phantoms were used to quantify the imaging performance parameters. The specific performance parameters that have been characterized are spatial resolution (as point spread function), linear measurement accuracy, contrast to noise ratio, and image uniformity, in both transmission and reflection imaging modalities.Results: The intrinsic in‐plane resolution was measured to be better than 1.5 mm and 1.0 mm for transmission and reflection modalities respectively. The linear measurement accuracy was measured to be, on average, approximately 1% for both the modalities. Speed of sound image uniformity and measurement accuracy were calculated to be 99.5% and <0.2% respectively. Contrast to noise ratio (CNR) measurements vary as a function of object size.Conclusions: The results show an improvement in the imaging performance of the system in comparison to earlier ultrasound tomography systems, which are applicable to clinical applications of the system, such as breast imaging.

In this paper, we demonstrate the ability of structured illumination microscopy to enhance the ability of fluorescence lifetime imaging to resolve fluorescence lifetimes in relatively thick samples that possess distinct but spectrally overlapping fluorescent layers. Structured illumination fluorescent lifetime imaging microscopy (SI-FLIM) is shown to be able to accurately reconstruct lifetime values in homogenous fluorophore samples (POPOP, NADH, and FAD) as well as accurately measure fluorescent lifetime in two layer models that are layered with NADH/FAD over POPOP, where NADH/FAD and POPOP have spectral overlap. Finally, the ability of SI-FLIM was demonstrated in a hamster cheek pouch ex vivo to show that more accurate lifetimes could be measured for each layer of interest in the oral mucosa (epithelium and submucosa).