PACS: Picture Archiving and Communication System

PACS: Picture Archiving and Communication System Feipei Lai National Taiwan University

PACS • A comprehensive computer system that is responsible for the electronic storage and distribution of medical images in the medical enterprise. • Reduce costs • Improve patient care

PACS 網路架構圖 1. Core Switch 6509 擺放位置兩台放置於東址資訊室，另外兩台放置於西址影醫部新增之機房 2.Main PACS client 連接方式 Client 端透過 Edge Switch 連接到 Core Switch上，每台 Edge Switch再分別透過光纖連結到不同的 Core Switch上做線路備援 3.舊有 RAD PACS 設備連接方式與線路更新西址影醫部相關網點均加以重新佈線，東址影醫部所新增之網點亦加以重新佈設，並於東址影醫部新增所需之機櫃放相關之設備。所有 RAD PACS的設備均將連接至新的 PACS Core Switch上，並針對相關的流量設定一個獨立的網段，讓不相干的人無法存取影醫部的 PACS資料。

4. 影醫高階設備數量與連接方式 東址影醫部高階設備為 30台，西址影醫部為 3台。連接方式為東址影醫新增一台48埠10/100/1000之交換器，西址影醫部新增一台24埠10/100/1000之交換器。然後再將設備利用光纖連接到 Core Switch上 5. 公館分院與總院間 RAD PACS存取方式為了相關資訊的存取安全性，目前有兩種作法 a.利用設備本身的控制功能，設定ACL之機制，限制相關的存取權限，讓只有影醫部的 IP才可存取 RAD PACS的資料。 b.直接拉專線做連結。

Various Network Technologies, Bandwidths and Typical Transfer Times

Evolution of Medical Tomographic Imaging – As Seen From a Darwinian Perspective • Imaging devices --- life-forms • Imager variability --- genes • Random appearance of new ideas --- mutations • Mass manufacture --- reproduction • Integration of different ideas --- generic recombination • Marketplace Pressures --- natural selection

Medical images • Topographic imaging • Represents the surface of the body • Projection imaging • The interactions of radiation penetrating along a known path of the radiation through the body • Tomographic imaging • The spatial distribution of the local interaction of the radiation with tissue in a thin slice through the body.

Medical images • The quality of the images is represented by contrast and resolution. • The contrast is determined by the nature of the interaction of the radiation with the tissue material (e.g., via partial absorption) or its structure (e.g., via reflection) or the preferential accumulation of indicator materials (e.g., iodine for X-ray, gadolinium 釓 for Magnetic Resonance Imaging, microbubles in the Ultrasound or radionuclides for Scintigraphy 閃爍造影術 ).

Medical images • The resolution is expressed as spatial, temporal or contrast. • Temporal resolution involves the exposure time required to complete the scan of a single image and the “frame rate” of the sequential individual images.

Medical images • Plays a major role in medical research activities such as detection and quantitation of pathophysiological structure-to-function relationships, drug discovery and phenotyping.

Imaging instrument • Components that generate the probing energy (such as electromagnetic radiation, ultrasound or electrical current) • The detector system • The tomographic image reconstructor (generally involves a mechanical or electronic scanning process and a variant of solving an inverse problem) • The image display (generally involves a computer terminal).

Novel ideas only survive if the environment for implementing the idea is present and/or the need is perceived.

PACS • Ultrasound • Magnetic Resonance Imaging • Computed Tomography

NMR • Lauterbur realized that the slight variation in magnet uniformity (the bane of spectroscopists) could be used to spatially localize the signal of interest and, hence, the controlled variation in magnetic field could form the basis of an imaging approach.

Ultrasound microbubbles • Intravascular microbubbles were developed as an ultrasound contrast agent, but the harmonic frequencies generated which “contaminated” the Doppler signal used to measure their velocity became the basis of a great increase in specificity and sensitivity of the microbubble use in ultrasound.

Chemical shift • The paramagnetic effect of oxygen in the blood could be used to generate highly specific images of cerebral oxygen use and spectroscopic evaluation of metabolic events in tissues such as in the brain and heart.

Positron Emission Tomography (PET) • Measures radioactive traces injected into the body

reference • Proceedings of the IEEE, Vol. 91, No. 10, October 2003, pp. 1483-1491.

Basic concepts in Image Generation • Spatial resolution • The number of pixels per image area • Contrast resolution • The number of bit per pixel determines the contrast resolution • Temporal resolution • A measure of the time needed to create an image

Ultrasound

Principle of Echo Scanners • In echo scanners, sound pulses are generated with frequencies of about a few MHz. These pulses are absorbed, scattered, or reflected in the patient. The reflections give rise to relatively strong echoes. • Reflections occur at interfaces between media that are different with respect to density and/or the velocity of sound (sound is reflected at interfaces with different acoustic impedances; the so-called acoustic impedance is equal to the product of sound velocity and density).

Principle of Echo Scanners • At an interface between soft tissue on one side and bone or air on the other side, a strong reflection is observed. • Scattering takes place if the dimension of the object is small (i.e., about the wavelength of the incident radiation). The beam is then scattered in all directions, and therefore, the amplitude of the signal detected by the transducer is relatively small.

Principle of Echo Scanners • The resolution of an echo scan, that is, the degree with which details located close together can still be distinguished, is determined by both the wavelength of the sound waves and the duration of the emitted pulse. • The pulse is usually several wavelengths long. In practice, therefore, reflections from two points separated by a few wavelengths can be discriminated. • The smaller the wavelength the better the resolution. Since the wavelength is inversely proportional to the frequency, the resolution is proportional to the frequency.

Principle of Echo Scanners • The attenuation coefficient (which expresses how much the beam is attenuated per centimeter of tissue because of scatter and absorption) is proportional to the sound frequency for soft tissue and is even proportional to the square of the frequency for other types of tissues. • The depth of penetration of the sound waves is inversely proportional to the frequency. The more the beam is attenuated, the more difficult it is to measure the reflections of deeper structures, since the signal-to-noise ratio gradually becomes smaller.

Principle of Echo Scanners • Since resolution and penetration depth pose contradictory requirements: • Deeper structures can only be visualized with relatively low frequencies, with a concomitant lower resolution. • The type of tissue influences the amount of absorption of the beam. Air and bone, for example, are strong absorbers, whereas muscle tissue and water hardly attenuate the beam.

Principle of Echo Scanners • At a frequency of 3 MHz (wavelength of 0.5 mm) depths of up to 10 cm are well visualized, with an axial resolution on the order of 1 mm. • For eye examinations a higher resolution is needed. In this case frequencies of between 5 and 13 MHz (wavelengths of between 0.25 and 0.075 mm, respectively) are used. • For brain examinations the sound beam must first pass bone structures (e.g., the tempora). Because of the high absorption of bone, especially for high frequencies, only low frequencies can be used, implying a lower resolution.

Temporal 太陽穴的,顳的 • The space, on either side of the head, back of the eye and forehead, above the zygomaticarch and in front of the ear.

The 2003 Nobel Prize in Physiology or Medicine • The Nobel Assembly at Karolinska Institutet awarded The Nobel Prize in Physiology or Medicine for 2003jointly to • Paul C Lauterbur and Peter Mansfield • for their discoveries concerning • "magnetic resonance imaging"

Summary • Imaging of human internal organs with exact and non-invasive methods is very important for medical diagnosis, treatment and follow-up. • Seminal discoveries concerning the use of magnetic resonance to visualize different structures. • These discoveries have led to the development of modern magnetic resonance imaging, MRI, which represents a breakthrough in medical diagnostics and research.

Atomic nuclei in a strong magnetic field rotate with a frequency that is dependent on the strength of the magnetic field. • Their energy can be increased if they absorb radio waves with the same frequency (resonance). • When the atomic nuclei return to their previous energy level, radio waves are emitted. • These discoveries were awarded the Nobel Prize in Physics in 1952.

When the atom is placed in a magnetic field, the interaction energy -∙B of the spin magnetic dipole moment with the field causes further splittings in energy levels and in the corresponding spectrum lines.

During the following decades, magnetic resonance was used mainly for studies of the chemical structure of substances. • In the beginning of the 1970s, this year’s Nobel Laureates made pioneering contributions, which later led to the applications of magnetic resonance in medical imaging.

Paul Lauterbur (born 1929), Urbana, Illinois, USA, discovered the possibility to create a two-dimensional picture by introducing gradients in the magnetic field. By analysis of the characteristics of the emitted radio waves, he could determine their origin. This made it possible to build up two-dimensional pictures of structures that could not be visualized with other methods.

Peter Mansfield (born 1933), Nottingham, England, further developed the utilization of gradients in the magnetic field. He showed how the signals could be mathematically analysed, which made it possible to develop a useful imaging technique. Mansfield also showed how extremely fast imaging could be achievable. This became technically possible within medicine a decade later.

Rapid development within medicine • A great advantage with MRI is that it is harmless according to all present knowledge. • The method does not use ionizing radiation, in contrast to ordinary X-ray (Nobel Prize in Physics in 1901) or computer tomography (Nobel Prize in Physiology or Medicine in 1979) examinations. • However, patients with magnetic metal in the body or a pacemaker cannot be examined with MRI due to the strong magnetic field, and patients with claustrophobia may have difficulties undergoing MRI.

Especially valuable for examination of the brain and the spinal cord • Today, MRI is used to examine almost all organs of the body. The technique is especially valuable for detailed imaging of the brain and the spinal cord. Nearly all brain disorders lead to alterations in water content, which is reflected in the MRI picture. A difference in water content of less than a percent is enough to detect a pathological change.

In multiple sclerosis 硬化症 , examination with MRI is superior for diagnosis and follow-up of the disease. • The symptoms associated with multiple sclerosis are caused by local inflammation in the brain and the spinal cord. • With MRI, it is possible to see where in the nervous system the inflammation is localized, how intense it is, and also how it is influenced by treatment.

Another example is prolonged lower back pain, leading to great suffering for the patient and to high costs for the society. • It is important to be able to differentiate between muscle pain and pain caused by pressure on a nerve or the spinal cord. • With MRI, it is possible to see if a disc herniation is pressing on a nerve and to determine if an operation is necessary.

Improved diagnostics in cancer • MRI examinations are very important in diagnosis, treatment and follow-up of cancer. • The images can exactly reveal the limits of a tumour, which contributes to more precise surgery and radiation therapy. • Before surgery, it is important to know whether the tumour has infiltrated the surrounding tissue. • MRI can more exactly than other methods differentiate between tissues and thereby contribute to improved surgery.

MRI has also improved the possibilities to ascertain the stage of a tumour, and this is important for the choice of treatment. • For example, MRI can determine how deep in the tissue a colon cancer has infiltrated and whether regional lymph nodes have been affected.

Magnetic Resonance Imaging • The aim of MRI is to provide an image of the tissue distribution in a plane through the body, for example, by measuring the hydrogen density in that plane. • The idea is, once again, to obtain a two-dimensional image of a two-dimensional slice through the body.

Principle of Magnetic Resonance Imaging • How can the density of hydrogen nuclei at each location of interest in the body be obtained? • The hydrogen atoms at each location have their own specific Larmor resonance frequency, depending on the local strength of the external magnetic field.

Principle of Magnetic Resonance Imaging • By irradiating the body with EM radiation at a certain frequency in a direction perpendicular to the external magnetic field, only those hydrogen nuclei that have a Larmor frequency equal to the frequency of the RF excitation pulse will resonate. • The Larmor frequency depends on the strength of the magnetic field, so these nuclei are located in a small volume.

Principle of Magnetic Resonance Imaging • The RF excitation pulse has such a duration that after the pulse the magnetization vector will process perpendicularly to the external magnetic field (the 90o RF pulse). • A current is then induced in a coil perpendicular to the external magnetic field. This current has an amplitude proportional to the number of the resonating nuclei in that volume and a frequency equal to the Larmor frequency.

Principle of Magnetic Resonance Imaging • This frequency determines the position of the sampled volume. This procedure is repeated with other frequencies for all volumes with a specific Larmor frequency. • By this procedure the density of hydrogen nuclei can be obtained at all locations of interest.

Principle of Magnetic Resonance Imaging • The external magnetic field consists of two parts: • a strong homogeneous field • a smaller magnetic field, of which the strength changes linearly in a certain direction. The linearly changing field can be applied in three directions by three orthogonally placed gradient coils. This changing magnetic field is also called the magnetic field gradient.

PACS: Picture Archiving and Communication System