Analisis Resolusi Spasial Citra MRI 1,5 T dengan Edge Spread Function

Resolusi Spasial merupakan salah satu parameter untuk menentukan kualitas citra pada MRI dengan membedakan antara dua titik secara terpisah dan jelas. Akuisisi data dilakukan menggunakan head coil phantom, Pesawat MRI 1.5 T, dengan variasi parameter scan. Analisis nilai Resolusi Spasial citra menggunakan software pengolahan citra sebagai alat pemroses citra dengan metode Edge Spread Function (ESF) kemudian dibandingkan dengan rumus voxel. Dimana voxel menentukan resolusi spasial. Hasil penelitian menunjukkan bahwa variasi ke 6 dari 21 variasi memiliki nilai resolusi spasial terbaik, terlihat dari nilai ESF tertinggi dan berkorelasi dengan voxel yang memiliki nilai terendah. Parameter yang biasa dipakai di rumah sakit untuk MRI 1,5 T merk General Electrical, memiliki nilai resolusi spasial lebih rendah dari variasi ke 6

UJI RESOLUSI SPASIAL DAN SLICE THICKNESS PADA CT SCAN 128 DAN 16 SLICE DENGAN MENGGUNAKAN PHANTOM QUART DVT-AP

CT-Scan adalah salah satu modalitas untuk diagnosis utama, kualitas citra dari CT-Scan sangat berpengaruh terhadap diagnosis. Untuk menguji kualitas citra CT-Scan diperlukan suatu alat ukur berupa phantom. Penelitian ini bertujuan untuk menganalisa penggunaan phantom Quart DVT-AP terhadap nilai resolusi spasial dan slice thickness pada CT-Scan 128 Slice dan 16 Slice. Uji resolusi spasial dan slice thickness dilakukan dengan menggunakan perhitungan dari citra digital. Phantom dipindai dengan melakukan variasi nilai slice thickness (2,5 , 5 , dan 10 mm). Penentuan nilai resolusi spasial dan slice thickness diperoleh dari nilai Edge Spread Function(ESF) menggunakan software bawaan phantom yaitu Quart CT-TEC dan juga Matlab. Kemudian digunakan juga phantom Gammex ACR untuk membandingkan nilai resolusi spasial dan slice thickness yang didapat menggunakan Quart DVT-AP.   Hasil penelitian ini menunjukan bahwa phantom Quart DVT-AP mampu mengukur slice thickness pada CT-Scan 128 dan 16 slice dan sanggup mengukur sampai pasangan garis ke 6 yaitu 0,9 Lp/mm, lebih tinggi jika dibandingkan dengan hasil yang didapat menggunakan phantom Gammex ACR. Variasi ketebalan slice tidak mempengaruhi hasil pengukuran resolusi spasial dan slice thickness dan hasil perhitungan dari software CTTEC menunjukkan hasil yang sama baiknya dengan Matlab. Nilai resolusi spasial dan slice thickness telah dibandingkan dengan nilai lolos uji sesuai rekomendasi BAPETEN, sehingga perangkat CT-Scan masih layak untuk digunakan.   Kata Kunci : Edge Spread Function(ESF), Phantom Quart DVT-AP, Resolusi Spasial,          Slice Thickness, Software CTTE

PSF Estimation by Gradient Descent Fit to the ESF

Calibration of scanners and cameras usually involves measuring the point spread function (PSF). When edge data is used to measure the PSF, the differentiation step amplifies the noise. A parametric fit of the functional form of the edge spread function (ESF) directly to the measured edge data is proposed to eliminate this. Experiments used to test this method show that the Cauchy functional form fits better than the Gaussian or other forms tried. The effect of using a functional form of the PSF that differs from the true PSF is explored by considering bilevel images formed by thresholding. The amount of mismatch seen can be related to the difference between the respective kurtosis factors

Segmented field electron conformal therapy with an electron multi-leaf collimator

Purpose: The purpose of this work was to investigate the potential of a prototype electron multi-leaf collimator (eMLC) to deliver segmented-field electron conformal therapy (ECT) and to improve dose homogeneity to the planning target volume (PTV) by feathering the abutting edge of the higher energy electron fields. Methods: Software was developed to define the eMLC leaf positions that most closely fit a general field shape. Electron beams (6-20 MeV) using a prototype eMLC were commissioned for the pencil beam dose algorithm in the Pinnacle treatment planning system. A discrete (5-step) Gaussian edge spread function was used to match electron dose penumbras of differing energies at a specified depth in a water phantom. The effect of 1D edge feathering on dose homogeneity was computed and measured for segmented-field ECT treatment plans for three 2D PTVs in a water phantom (depths varied along axis parallel to leaf motion) and one 3D PTV (depth varied along both axes normal to beam). Additionally, the effect of 2D edge feathering was computed for the 3D PTV. Results: 1D discrete Gaussian edge feathering reduced the standard deviation of dose in the 2D PTVs by 34, 34, and 39%. In the 3D PTV, 1D discrete Gaussian edge feathering reduced the standard deviation of dose by 19%. The physical constraints (1-cm leaf width) of the eMLC hindered the 2D application of the feathering solution to the 3D PTV, and the standard deviation of dose increased by 10%. However, 2D discrete Gaussian edge feathering with a smooth-aperture (infinitesimal leaf width) reduced the standard deviation of dose in the 3D PTV by 33%. Conclusions: A 5-step discrete Gaussian edge spread function applied in 2D improves the abutment dosimetry but requires an eMLC leaf resolution better than 1 cm

Time-gated transillumination of biological tissues and tissuelike phantoms

The applicability and limits of time-resolved transillumination to determine the internal details of biological tissues are investigated by phantom experiments. By means of line scans across a sharp edge, the spatial resolution (Ax) and its dependence on the time-gate width (At) can be determined. Additionally, measurements of completely absorbing bead pairs embedded in a turbid medium demonstrate the physical resolution in a more realistic case. The benefit of time resolution is especially high for a turbid medium with a comparatively small reduced scattering coefficient of approximately pL,' = 0.12 mm-1. Investigations with partially absorbing beads and filled plastic tubes demonstrate the high sensitivity of time-resolving techniques with respect to spatial variations in scattering or absorption coefficients that are due to the embedded disturber. In particular, it is shown that time gating is sensitive to variations in scattering coefficients. Key words: Time-resolved transillumination, turbid media, light scattering, streak camera

Comparison between edge tracing and slit tracing in the measurement of the OTF

A study was performed to compare two methods of measuring the Optical Transfer Function (OTF), namely edge tracing and slit tracing, to evaluate the performances and limitations of each method. Edge tracing is a very common method of measuring the OTF of an optical system. It is simple to set up, but the sampling size is limited and derivation of the Edge Spread Function is required in order to obtain the Line Spread Function (LSF). This derivation induces considerable high frequency noise. A competing method, slit tracing, is more complex mainly because of physical limitations such as the actual slit width. It has the advantages of directly providing the Line Spread Function (LSF), and having constant noise over all frequencies. Both methods gave equally good results at low noise levels, but Edge tracing was found to be advantageous at higher noise levels

Time-resolved transillumination of turbid media

The suitability and limits of time-resolved transillumination to determine inner details of biological tissues are investigated by phantom experiments. The achievable improvement is demonstrated by using different phantoms (absorbing objects embedded in a turbid medium). By means of line-scans across a sharp edge the spatial resolution and its dependence on temporal resolution can be determined. To demonstrate the physical resolution according to the Rayleigh-criterion, measurements were performed on blackened bead pairs. Investigations with partially transparent beads demonstrate the high sensitivity of time-resolving techniques with respect to variations in scattering or absorption coefficients

Towards Streamlined Single-Image Super-Resolution: Demonstration with 10 m Sentinel-2 Colour and 10-60 m Multi-Spectral VNIR and SWIR Bands

Higher spatial resolution imaging data are considered desirable in many Earth observation applications. In this work, we propose and demonstrate the TARSGAN (learning Terrestrial image deblurring using Adaptive weighted dense Residual Super-resolution Generative Adversarial Network) system for Super-resolution Restoration (SRR) of 10 m/pixel Sentinel-2 “true” colour images as well as all the other multispectral bands. In parallel, the ELF (automated image Edge detection and measurements of edge spread function, Line spread function, and Full width at half maximum) system is proposed to achieve automated and precise assessments of the effective resolutions of the input and SRR images. Subsequent ELF measurements of the TARSGAN SRR results suggest an averaged effective resolution enhancement factor of about 2.91 times (equivalent to ~3.44 m/pixel for the 10 m/pixel bands) given a nominal SRR upscaling factor of 4 times. Several examples are provided for different types of scenes from urban landscapes to agricultural scenes and sea-ice floes

Collinear, two-color optical Kerr effect shutter for ultrafast time-resolved imaging

Imaging with ultrashort exposure times is generally achieved with a crossed-beam geometry. In the usual arrangement, an off-axis gating pulse induces birefringence in a medium exhibiting a strong Kerr response (commonly carbon disulfide) which is followed by a polarizer aligned to fully attenuate the on-axis imaging beam. By properly timing the gate pulse, imaging light experiences a polarization change allowing time-dependent transmission through the polarizer to form an ultrashort image. The crossed-beam system is effective in generating short gate times, however, signal transmission through the system is complicated by the crossing angle of the gate and imaging beams. This work presents a robust ultrafast time-gated imaging scheme based on a combination of type-I frequency doubling and a collinear optical arrangement in carbon disulfide. We discuss spatial effects arising from crossed-beam Kerr gating, and examine the imaging spatial resolution and transmission timing affected by collinear activation of the Kerr medium, which eliminates crossing angle spatial effects and produces gate times on the order of 1 ps. In addition, the collinear, two-color system is applied to image structure in an optical fiber and a gasoline fuel spray, in order to demonstrate image formation utilizing ballistic or refracted light, selected on the basis of its transmission time.Comment: 13 pages, 10 figure