Technical Note: Fully-automated analysis of Jaszczak phantom measurements as part of routine SPECT quality control.

Purpose: Inspection and quantitative validation of tomographic imaging properties of SPECT systems, i.e., spatial resolution, contrast, and inhomogeneity must be performed in regular intervals.

A quantitative comparison of the performance of three deformable registration algorithms in radiotherapy.

We present an evaluation of various non-rigid registration algorithms for the purpose of compensating interfractional motion of the target volume and organs at risk areas when acquiring CBCT image data prior to irradiation. Three different deformable registration (DR) methods were used: the Demons algorithm implemented in the iPlan Software (BrainLAB AG, Feldkirchen, Germany) and two custom-developed piecewise methods using either a Normalized Correlation or a Mutual Information metric (featureletNC and featureletMI). These methods were tested on data acquired using a novel purpose-built phantom for deformable registration and clinical CT/CBCT data of prostate and lung cancer patients.

Monitoring tumor motion by real time 2D/3D registration during radiotherapy.

Background And Purpose: In this paper, we investigate the possibility to use X-ray based real time 2D/3D registration for non-invasive tumor motion monitoring during radiotherapy.

Materials And Methods: The 2D/3D registration scheme is implemented using general purpose computation on graphics hardware (GPGPU) programming techniques and several algorithmic refinements in the registration process. Validation is conducted off-line using a phantom and five clinical patient data sets.

High-performance GPU-based rendering for real-time, rigid 2D/3D-image registration and motion prediction in radiation oncology.

A common problem in image-guided radiation therapy (IGRT) of lung cancer as well as other malignant diseases is the compensation of periodic and aperiodic motion during dose delivery. Modern systems for image-guided radiation oncology allow for the acquisition of cone-beam computed tomography data in the treatment room as well as the acquisition of planar radiographs during the treatment. A mid-term research goal is the compensation of tumor target volume motion by 2D/3D Registration.

Comparison of advanced iterative reconstruction methods for SPECT/CT.

Aim: Corrective image reconstruction methods which produce reconstructed images with improved spatial resolution and decreased noise level became recently commercially available. In this work, we tested the performance of three new software packages with reconstruction schemes recommended by the manufacturers using physical phantoms simulating realistic clinical settings.

Methods: A specially designed resolution phantom containing three (99m)Tc lines sources and the NEMA NU-2 image quality phantom were acquired on three different SPECT/CT systems (General Electrics Infinia, Philips BrightView and Siemens Symbia T6).

Validation for 2D/3D registration. II: The comparison of intensity- and gradient-based merit functions using a new gold standard data set.

Purpose: A new gold standard data set for validation of 2D/3D registration based on a porcine cadaver head with attached fiducial markers was presented in the first part of this article. The advantage of this new phantom is the large amount of soft tissue, which simulates realistic conditions for registration. This article tests the performance of intensity- and gradient-based algorithms for 2D/3D registration using the new phantom data set.

PET based volume segmentation with emphasis on the iterative TrueX algorithm.

Purpose: To assess the influence of reconstruction algorithms for positron emission tomography (PET) based volume quantification. The specifically detected activity in the threshold defined volume was investigated for different reconstruction algorithms as a function of volume size and signal to background ratio (SBR), especially for volumes smaller than 1ml. Special attention was given to the Siemens specific iterative reconstruction algorithm TrueX.

Stochastic rank correlation: a robust merit function for 2D/3D registration of image data obtained at different energies.

In this article, the authors evaluate a merit function for 2D/3D registration called stochastic rank correlation (SRC). SRC is characterized by the fact that differences in image intensity do not influence the registration result; it therefore combines the numerical advantages of cross correlation (CC)-type merit functions with the flexibility of mutual-information-type merit functions. The basic idea is that registration is achieved on a random subset of the image, which allows for an efficient computation of Spearman's rank correlation coefficient.

A comparative study on manual and automatic slice-to-volume registration of CT images.

In order to assess the clinical relevance of a slice-to-volume registration algorithm, this technique was compared to manual registration. Reformatted images obtained from a diagnostic CT examination of the lower abdomen were reviewed and manually registered by 41 individuals. The results were refined by the algorithm.

Multiple window spatial registration error of a gamma camera: 133Ba point source as a replacement of the NEMA procedure.

Background: The accuracy of multiple window spatial resolution characterises the performance of a gamma camera for dual isotope imaging. In the present study we investigate an alternative method to the standard NEMA procedure for measuring this performance parameter.

Methods: A long-lived 133Ba point source with gamma energies close to 67Ga and a single bore lead collimator were used to measure the multiple window spatial registration error.

The Zernike expansion--an example of a merit function for 2D/3D registration based on orthogonal functions.

Current merit functions for 2D/3D registration usually rely on comparing pixels or small regions of images using some sort of statistical measure. Problems connected to this paradigm the sometimes problematic behaviour of the method if noise or artefacts (for instance a guide wire) are present on the projective image. We present a merit function for 2D/3D registration which utilizes the decomposition of the X-ray and the DRR under comparison into orthogonal Zernike moments; the quality of the match is assessed by an iterative comparison of expansion coefficients.

2D/3D registration of endoscopic ultrasound to CT volume data.

This paper describes a computer-aided navigation system using image fusion to support endoscopic interventions such as the accurate collection of biopsy specimens. An endoscope provides the physician with real-time ultrasound (US) and a video image. An image slice that corresponds to the corresponding image from the US scan head is derived from a preoperative computed tomography (CT) or magnetic resonance image volume data set using oblique reformatting and displayed side by side with the US image.

Fast DRR splat rendering using common consumer graphics hardware.

Digitally rendered radiographs (DRR) are a vital part of various medical image processing applications such as 2D/3D registration for patient pose determination in image-guided radiotherapy procedures. This paper presents a technique to accelerate DRR creation by using conventional graphics hardware for the rendering process. DRR computation itself is done by an efficient volume rendering method named wobbled splatting.

Comparison of laser surface scanning and fiducial marker-based registration in frameless stereotaxy. Technical note.

The authors compared the accuracy of laser surface scanning patient registration using the commercially available Fazer (Medtronic, Inc.) with the conventional registration procedure based on fiducial markers (FMs) in computer-assisted surgery. Four anatomical head specimens were prepared with 10 titanium microscrews placed at defined locations and scanned with a 16-slice spiral computed tomography unit.

Rigid 2D/3D slice-to-volume registration and its application on fluoroscopic CT images.

Registration of single slices from FluoroCT, CineMR, or interventional magnetic resonance imaging to three dimensional (3D) volumes is a special aspect of the two-dimensional (2D)/3D registration problem. Rather than digitally rendered radiographs (DRR), single 2D slice images obtained during interventional procedures are compared to oblique reformatted slices from a high resolution 3D scan. Due to the lack of perspective information and the different imaging geometry, convergence behavior differs significantly from 2D/3D registration applications comparing DRR images with conventional x-ray images.

Esophageal acid exposure in upright and recumbent postures: roles of lower esophageal sphincter, esophageal contractile and transport function, hiatal hernia, age, sex, and body mass.

This study aimed to assess, using multiple regression analyses, the roles of lower esophageal sphincter, esophageal contractile and transport function, hiatal hernia, age, sex, and body mass for esophageal acid exposure in upright and recumbent postures and for esophagitis. In 116 patients with reflux symptoms, acid exposure was recorded by 24-hr pH monitoring, motility manometrically, bolus transport scintigraphically, hiatal hernia and esophagitis endoscopically. In upright posture, the percentage time at pH <4 increased significantly with higher body mass index and lower distal esophageal amplitude, the number of episodes >5 min at pH <4 with lower distal amplitude, slower transport, and higher body mass, and the longest episode at pH <4 with lower distal amplitude.

[Evaluation of the performance of a gamma camera equipped with a 5/8" versus 1" thick NaI detector].

The upgrade of a gamma camera from a 5/8" to a 1" thick crystal, the latter with StarBrite technology, prompted to the investigation of changes in performance parameters for planar scintigraphy and SPECT as well as for PET in coincidence mode. For planar and SPECT parameters, the performance was measured according to NEMA Standard Protocol NU1-2001. No changes were found in terms of intrinsic uniformity, intrinsic spatial resolution, linearity, energy resolution, system resolution, and tomographic system resolution.

A fully automated calibration method for an optical see-through head-mounted operating microscope with variable zoom and focus.

Ever since the development of the first applications in image-guided therapy (IGT), the use of head-mounted displays (HMDs) was considered an important extension of existing IGT technologies. Several approaches to utilizing HMDs and modified medical devices for augmented reality (AR) visualization were implemented. These approaches include video-see through systems, semitransparent mirrors, modified endoscopes, and modified operating microscopes.

Design and application of an assessment protocol for electromagnetic tracking systems.

This paper defines a simple protocol for competitive and quantified evaluation of electromagnetic tracking systems such as the NDI Aurora (A) and Ascension microBIRD with dipole transmitter (B). It establishes new methods and a new phantom design which assesses the reproducibility and allows comparability with different tracking systems in a consistent environment. A machined base plate was designed and manufactured in which a 50 mm grid of holes was precisely drilled for position measurements.

Variations in the output power and surface heating effects of transducers in therapeutic ultrasound.

Objective: To determine the real emitted output power and maximum surface heating of commercial therapeutic ultrasound transducers emitting in air for various therapeutic regimens.

Design: Surface temperatures of ultrasound transducers with frequencies of .05 to 3 MHz were detected over 5 minutes by using a calibrated infrared thermographic camera; additionally, the indicated output power was checked with a radiation force balance.

Design and application of an assessment protocol for electromagnetic tracking systems.

This paper defines a simple protocol for competitive and quantified evaluation of electromagnetic tracking systems such as the NDI Aurora (A) and Ascension microBIRD with dipole transmitter (B). It establishes new methods and a new phantom design which assesses the reproducibility and allows comparability with different tracking systems in a consistent environment. A machined base plate was designed and manufactured in which a 50 mm grid of holes was precisely drilled for position measurements.

An inter-laboratory comparison study of image quality of PET scanners using the NEMA NU 2-2001 procedure for assessment of image quality.

An inter-laboratory comparison study was conducted to assess the image quality of PET scanners in Austria. The survey included both dedicated PET scanners (D-PET, n = 8) and coincidence cameras (GC-PET, n = 7). Measurement of image quality was based on the NEMA (National Electrical Manufacturers Association) NU 2-2001 protocol and the IEC (International Electrotechnical Commission) body phantom.

Stability of miniature electromagnetic tracking systems.

This study aims at a comparative evaluation of two recently introduced electromagnetic tracking systems under reproducible simulated operating-room (OR) conditions: the recently launched Medtronic StealthStation, Treon-EM and the NDI Aurora. We investigate if and to what extent these systems provide improved performance and stability in the presence of surgical instruments as possible sources of distortions compared with earlier reports on electromagnetic tracking technology. To investigate possible distortions under pseudo-realistic OR conditions, a large Langenbeck hook, a dental drill with its handle and an ultrasonic (US) scanhead are fixed on a special measurement rack at variable distances from the navigation sensor.

Wobbled splatting--a fast perspective volume rendering method for simulation of x-ray images from CT.

3D/2D registration, the automatic assignment of a global rigid-body transformation matching the coordinate systems of patient and preoperative volume scan using projection images, is an important topic in image-guided therapy and radiation oncology. A crucial part of most 3D/2D registration algorithms is the fast computation of digitally rendered radiographs (DRRs) to be compared iteratively to radiographs or portal images. Since registration is an iterative process, fast generation of DRRs-which are perspective summed voxel renderings-is desired.

Robot-assisted biopsy using computed tomography-guidance: initial results from in vitro tests.

Purpose: We sought to develop a robotic system for computed tomography (CT)-guided biopsy to validate the feasibility, accuracy, and efficacy of the system using phantom tests.

Materials And Methods: Ten peas (mean diameter 9.9+/-0.