Fluke 76-907, 76-908 user manual Signal-To-Noise Ratio, High-Contrast Spatial Resolution

Page 13

Operation

2

Tests with 3D Resolution and Slice (3DRAS) Phantom

resonance frequency adjustment and some may be completely automated. Resonance frequency should be recorded daily for trend analysis.

Values of resonance frequency should generally not deviate by more than 50 ppm between successive daily measurements.

2.3.2 Signal-To-Noise Ratio

The signal is defined as the mean pixel value within the region-of-interest minus any pixel offset. Noise is defined as the random variations in pixel intensity. Images with obvious artifacts are not suitable for signal-to-noise ratio (SNR) determinations.

Factors contributing to variations in signal-to-noise include:

(I)General system calibration (resonance frequency, flip angles)

(2) Slice thickness

(3) Coil tuning

(4) RF shielding

(5) Coil loading

(6) Image processing

(7) Scan parameters (TR, TE)

(8) T-1 and T-2 solution values

When using large volume fluid-filled phantoms, it should be recognized that thermal and mechanically induced motions can introduce artifacts. The unloaded coil allows the evaluation of system noise that is the parameter of interest. In a clinical scan, it is recognized that the patient is the dominant source of noise. In order to approximate the clinical situation, the coil must be electrically loaded by using an appropriate filler material.

The signal is measured using a ROI that contains at least 100 pixels or 10% of the area of the signal producing material, whichever is greater. The ROI should be positioned in the center of the image and should not include any obvious artifacts. The signal is the mean value of the pixel intensity in the ROI minus any offset. (An indication of the existence of an image intensity offset may be gained from an examination of intensity values from ROl's taken over non-signal producing portions of a phantom. Specific offset values should be obtained from the system manufacturer). The noise is the standard deviation derived from the same ROI. The signal-to-noise ratio is then calculated.

2.3.3 High-Contrast Spatial Resolution

High contrast spatial resolution is a measure of the capacity of an imaging system to show separation of objects when there is no significant noise contribution. High contrast spatial resolution for MRI systems is typically limited by pixel size (field-of-view divided by the sampling in x or y). Traditionally, resolution has been quantified by the point spread function (PSF), line spread function (LSF), or modulation transfer function (MTF); however, these methods are not practical for routine measurements. Therefore, a visual evaluation of test objects is used.

Factors contributing to high-contrast resolution include:

•Field-of-view (determined by gradient strength, acquisition matrix, sampling period), and image reconstruction and display method.

•The image will be evaluated visually. Image analysis consists of viewing the image to determine the smallest resolvable hole array (magnification may be used if desired). For an array to be resolved, all holes and spaces must be displayed as separate and distinct then viewed with the narrowest window width. The window level should be adjusted for optimum visualization.

2-3

Page 12 Page 14
Image 13
Page 12 Page 14
Contents Aapm MRI Phantoms Nuclear Associates 76-907Fluke Biomedical Table of Contents Blank Phantom Description IntroductionOuter Shape 6 X 6 X 5 Cubical Box 1 3D Resolution and Slice 3DRAS Phantom ModelMm Gap Slice Thickness Sections Uniformity and Linearity UAL PhantomUAL Phantom with Side View Nuclear Associates 76-908 Phantom Preparation 1Signal Producing Solution2Filling the Phantom Preparation for Scanning Tests with 3D Resolution and Slice 3DRAS PhantomPositioning the Phantom Scanning ParametersHigh-Contrast Spatial Resolution Signal-To-Noise RatioSlice Position and Separation Slice ThicknessExample Images Nuclear Associates 76-908 Operation Tests with 3D Resolution and Slice 3DRAS Phantom Nuclear Associates 76-908 Operation Tests with 3D Resolution and Slice 3DRAS Phantom Image Uniformity Tests With Uniformity and Linearity UAL PhantomSpatial Linearity Distortion Operation Tests with Uniformity and Linearity UAL Phantom Image ArtifactsAction Criteria DC-Offset ErrorsOperation Tests with Uniformity and Linearity UAL Phantom Nuclear Associates 76-908 Operation Tests with Uniformity and Linearity UAL Phantom Fluke Corporation

76-908, 76-907 specifications

The Fluke 76-907 and 76-908 are advanced digital multimeters designed to cater to the needs of professionals and technicians in diverse fields. Known for their accuracy, durability, and versatility, these instruments have become essential tools for electrical measurement and troubleshooting.

One of the standout features of both the Fluke 76-907 and 76-908 is their superior measurement capabilities. These multimeters can measure AC and DC voltage, current, resistance, frequency, and temperature with impressive precision. The devices are equipped with a large LCD display that provides clear readings, even in low-light conditions, making it easy for users to take measurements in various environments.

The Fluke 76-907 is particularly recognized for its ergonomic design, ensuring comfort during prolonged use. It includes a built-in flashlight to illuminate dark work areas and an adjustable backlight for improved visibility of the display. Additionally, the device features a rugged casing that protects it from drops and impacts, enhancing its longevity and reliability in demanding job sites.

On the other hand, the Fluke 76-908 offers advanced features such as Bluetooth connectivity, enabling users to connect the meter to compatible smartphones and tablets. This feature allows for seamless data transfer and real-time monitoring of measurements via an intuitive app. The integration of wireless technology facilitates remote measurements, which is crucial in hazardous environments where direct access may be restricted.

Both models utilize advanced technology, including True RMS measurements, which ensure accurate readings of complex signals. This is particularly beneficial for professionals working with variable frequency drives, non-linear loads, and harmonics. The Fluke 76-907 and 76-908 also come equipped with a range of safety features, including CAT III and CAT IV ratings, ensuring they can safely handle high-voltage applications.

Battery life is another essential characteristic of these multimeters. Both models are designed for extended usage with efficient power management systems, minimizing downtime caused by battery replacements.

Furthermore, the Fluke 76-907 and 76-908 are straightforward to operate, featuring a user-friendly interface that allows technicians to navigate functions easily. They are ideal for various applications, from routine maintenance and troubleshooting in electrical systems to complex diagnostics in industrial settings.

In conclusion, the Fluke 76-907 and 76-908 digital multimeters stand out for their precise measurements, robust design, and innovative technology. Whether for fieldwork or onsite diagnostics, these multimeters provide reliability and efficiency, making them indispensable tools for professionals in the electrical industry.
Top Page Image Contents