Medical Physics

medical, physics Physics sector that develops research relating to human health problems using the principles and methods of physics. It uses the knowledge acquired in both the physics and the medical-biological fields in various ways and is involved in many aspects of health care programs, as it is able to specify the physical parameters essential for their implementation. . The result is therefore a large number of fields of activity concerning the use of measuring instruments, the diagnostic and therapeutic application of radionuclides, radiotherapy.

Computerized bone mineralometry ( ➔ MOC ) is one of the increasingly important measurement techniques , with which the quantity and distribution of calcium in bones is determined. Computerized axial tomography (CT or, more precisely, CT) and subsequent generations of CT scanners have revolutionized not only radiodiagnostics, but also monitoring for the clinical progress of patients (➔ tomography ). A pioneering tomography for functional brain images is PET . Another widely used imaging technique isSPECT.

Techniques such as NMR ( nuclear magnetic resonance ) or MRI ( magnetic resonance imaging ) reveal detailed anatomical information especially of the brain ( ➔ resonance ). The ability of functional magnetic resonance imaging (FMRI ) to provide information on minimal local variations in brain blood flow and other parameters sensitive to brain activity has opened important research fields on various problems, such as the construction of the side part map brain related to speech, language, perception of pain, the evolution of epilepsy and apoplexy. MRA ( magnetic resonance angiography) is taking over arterial angiography as a means of providing an image of the blood vessels of the brain and other body areas (aorta, peripheral circulation). MRS ( magnetic resonance spectroscopy ) instead provides useful information on the phenomena that underlie important diseases. For example, in the case of trauma or certain pathologies, it gives information on the mechanisms of alterations in the chemical composition and energy levels of the various brain regions.

The radiation synchrotron allows to adopt innovative techniques in a wide range of biomedical applications. In particular, extremely promising results have been obtained using radiation sources in the field of basic research for clinical use, such as in the case of DSA ( digital subtraction angiography ), mammography, radiotherapy and early diagnosis to identify abnormal calcium distributions in bones.

Another widely used and increasingly refined technique is the ecodoppler ( ➔ ultrasound ).

IN-DEPTH ABSTRACTfrom Ida Ortalli Medical Physics (Encyclopedia of Science and Technology)

  1. Recent developments

Optical fibers, in which light can completely propagate from one end to the other, have been used since the 1960s. for endoscopic diagnostics. The ability to remotely transport an image has allowed the consolidation of various endoscopic techniques in medicine. Optical fibers, if associated with laser light, can be used in vivo, with significant diagnostic interest. In the last twenty years, many developments in physics applied to medicine have been made in the field of images, signal analysis, computers for diagnostics, robotics, rehabilitation and joint equipment, heart valves , the production of biosensors, biomaterials and surgical instruments. The area of ​​bioimagery includes those methods capable of measuring in vivo and representing, in the form of images, the spatio-temporal distribution and variation of physical, functional or biochemical variables. It is conventionally divided into the area of ​​ionizing techniques (nuclear medicine, radiology, CT) and the area of ​​non-ionizing techniques (NMR, ultrasound, thermography, bioelectromagnetism).

The introduction of CT (axial computed tomography) and subsequent generations of CT scanners have led to a profound change in X-ray diagnostics, through the production of high quality images for the axial sections of the body. The CT allows to reconstruct images of cross sections with the aid of a calculator. Not only has radiography revolutionized, but also the clinical progress of patients, especially those of neurosurgical interest. Another tomography is that with positron emission, called PET (Positron emission tomography), which through the use of specific radioactive tracers allows to visualize the body’s metabolic functions; for example, it allows the visualization of glucose and oxygen metabolism in brain regions, following administration of radiopharmaceuticals. PET has also allowed advancement in knowledge about dementia; it can help in the study of the processes associated with epilepsy, brain tumors, Parkinson’s disease; combined with electroencephalography and magnetoencephalography it allows to understand the complex interactions between the metabolic and electrical activities of the brain. PET therefore provides functional diagnostic information complementary to that of the morphostructural type provided by ultrasound, CT and nuclear magnetic resonance. SPECT (Single photon emission computed tomography), is another, less expensive and less complex technique, useful for studying the phenomena of perfusion in the brain and the alterations of the blood vessels responsible, under certain conditions,

The nuclear magnetic resonance NMR (Nuclear magnetic resonance), or MRI (Magnetic resonance imaging), finds application in the case of nuclear species with non-zero magnetic moment and provides for the application of a static magnetic field and radio frequency electromagnetic waves. Among the many chemical elements of biological interest that can be analyzed by NMR, hydrogen is of particular importance for in vivo application, because it is abundant in biological tissues, has a high magnetic moment and has spin 1/2, which corresponds to a single line of resonance. The use of NMR in the medical field is relatively recent: it dates back to the early seventies, and already in 1977 the first prototypes were built capable of containing the entire human body within the magnets and of giving axial representations (whole body NMR). The images obtained represent the distribution of mobile protons, such as those contained in the water present in the various tissues: hydrogen is very mobile in the soft tissue context, while it is much less mobile in rigid structures, and for this reason the soft tissues give excellent signals and satisfactory images, while in bones the NMR signal does not contribute to the formation of images.

NMR analyzes reveal detailed anatomical information, especially of the brain, particularly when using eco-planar images. Functional nuclear magnetic resonance imaging (fMRI) has also recently become available. The ability of fMRI to provide information on minimal local variations in brain blood flow and other parameters sensitive to brain activity has opened up important fields of research on various problems, such as the construction of the map of the lateral part of the brain related to the word, language, the perception of pain, the evolution of epilepsy and apoplexy. Magnetic resonance angiography (MRA) is taking over from arterial angiography as a means of providing an image of the brain’s blood vessels. MRS (Magnetic resonance spectroscopy) provides useful information on the phenomena that underlie important diseases. In the case of trauma or disease, it provides information on the mechanisms of alterations in the chemical composition and energy levels of the different brain regions. MRI has been used successfully to detect brain tumors, proposing a more important clinical role than MRS because it avoids the need for brain inspection. However, apart from the high costs, MRI techniques continue to present a number of problems that need to be solved. provides information on the mechanisms of alterations in the chemical composition and energy levels of the different brain regions. MRI has been used successfully to detect brain tumors, proposing a more important clinical role than MRS because it avoids the need for brain inspection. However, apart from the high costs, MRI techniques continue to present a number of problems that need to be solved. provides information on the mechanisms of alterations in the chemical composition and energy levels of the different brain regions. MRI has been used successfully to detect brain tumors, proposing a more important clinical role than MRS because it avoids the need for brain inspection. However, apart from the high costs, MRI techniques continue to present a number of problems that need to be solved.

Sound waves at much higher frequencies than those audible to the human ear can also be used in the medical field. Ultrasonography combined with eco-detection techniques has proved to be very valuable. The instrumentation used is Doppler ultrasound based on the Doppler effect, and it is becoming increasingly refined. The most common application of the eco-Doppler is the double analyzer, through which two two-dimensional images are acquired in real time, used for a three-dimensional vision that also allows you to provide photographic or film images. This type of ultrasound allows to evaluate the health status of the fetus and to follow, throughout the pregnancy, not only its anatomy, but also its behaviors and movements.

Eco-Doppler is also increasingly used in arteriography, to evaluate patients with suspected cervical internal carotid artery lesions. Other uses are the study of blood flow and the detection of fetal heart movements. It can also be used to check the profile of the speed of blood through the blood vessels and to detect the progress of a vessel inside the abdomen. Another important field of application is that of vascular cardiology.

Synchroton radiation has recently been added to these techniques, which offers unique possibilities for diagnostic imaging applications and guarantees a real therapeutic approach. It is a broad spectrum technique, as it allows to adopt innovative technologies for numerous applications in the biomedical field. In particular, extremely promising results have been obtained in the case of digital subtraction angiography, mammography, radiotherapy and early diagnosis of abnormal calcium distributions in the bones. The results obtained in mammography showed high contrast images, able to highlight dense nodules, much smaller than those observed using conventional techniques. In each of these specific areas, the activities relating to the processing or display of the images are relevant, regardless of the specific application context. It brings together contributions from various sectors: physics, engineering, medicine, computer science, chemistry, biology, and it is difficult to identify a specific disciplinary contribution. There is a interpenetration of roles which, very often, is the best index of the success of interdisciplinary integration and, at the same time, a fundamental requirement for the advancement and development of this area.

  1. Research in the fight against cancer

In the last decade, considerable progress has been made not only in regards to diagnostics, but also for research in the fight against cancer. Already in 1903 Albert Jesoniek and Hermann von Tappeiner made an attempt at anticancer treatment, marking cell cultures with agents sensitive to visible light and then irradiating them with the latter. The results were satisfactory, but the times were not, so to speak, mature, so these searches had not followed for decades. These techniques were resumed only in the seventies, and until the nineties there was a real explosion of interest in therapies based on photoinactivation PDT (Photo-dynamic therapy). Photoinactivating therapies, however effective, however, are limited to the treatment of superficial tumors or cavities.

There are techniques that aim to inactivate cancer cells through the combined action of appropriate sensitizing substances and low energy radiation, an approach that has also had an intense development recently. Cellular inactivation couples the destructive capacity of ionizing radiation, normally gamma radiation, with selectivity towards cancer cells. The therapy consists in selectively bringing the so-called target isotopes onto the neoplastic cells and therefore in irradiating the mass with gamma radiation. Since the effect is only relevant for the sites containing the targets, i.e. tumor cells, selective destruction of the neoplastic mass can in principle occur. This methodology is very recent and still being tested.

The experimentation of hadron therapy is underway in the United States, Russia, Canada, Switzerland and also in Italy, which uses protons accelerators and other hadronic particles, i.e. heavy particles such as neutrons, protons and nuclei, produced by machines accelerators such as synchrotron. The main advantage of this particular type of radiation therapy is that, in addition to allowing a better distribution of the radiation, it should allow to increase the dose addressed to the tumor without thereby increasing the one that affects the healthy tissues or nearby critical organs. A second advantage should come from the elimination, or reduction, of the oxygen factor, which is still a serious problem in radiotherapy, as it is related to hypoxic cells, the most radioresistant ones. The global situation, from the point of view of both therapeutic response and efficacy, it is not yet clear. The results obtained so far show that compared to conventional therapy, hadrontherapy has a certain clinical advantage in the case of eye tumors (uveal melanomas and chondrosarcomas). The high cost should also be assessed according to the number of cases for which an actual clinical advantage is expected.

A new and original therapy in the treatment of cancer is that by means of boron neutron capture by boron (BNCT, Boron neutron capture therapy), aimed at cancer spread in the organs, a pathology devoid of remedial remedies. This study, inaugurated in 1987, exploits the great absorption capacity of boron isotope 10 by cancer cells. The method consists in irradiating the explanted organ, such as the liver, with neutrons after enriching the tissues with the boron isotope 10. The metastatic liver is explanted, placed inside a nuclear reactor and irradiated with a homogeneous beam of neutrons, capable of causing the disintegration of the boron nuclei and consequently the complete destruction of the neoplastic cells, almost without harm to healthy cells. The doses are due to the passage, in the cells,10 B (n, a) 7 Li. The therapeutic action is not due to the radiation coming from outside on the patient, but to the particles produced inside the cancer cell: the alpha particles and the lithium ions are released by the reaction between the neutrons and the boron-containing target, which functions as a microscopic ‘mine’ exploding inside the cell. In a time between 2 and 3.5 hours from the administration of the borated solution, lethal doses (60470 Gy-Eq) in the tumor and doses under the tolerance limit (8418 Gy-Eq) in healthy tissue are released. The results on the treated patients are very promising.

 

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