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Medical Imaging Technology

Page history last edited by Andrew P. Miller 7 years, 6 months ago

 

Medical Imaging Technology: From the Beginning until Now

 

By: Andrew P. Miller 

 

  

 

"The surgical imagination can pleasurably lose itself in devising endless applications of this wonderful process." -NY Times on the discovery of the X-Ray [1] 

 


 

Abstract

Medical imaging has has allowed for the advancement of medical and surgical care for patients during the past century.  William Conrad Rotgen, a German physicist, was the first individual to quantitatively produce a wavelength of radiation that is consistent with the modern day X-ray [9], and helped set in motion the rapid technological advents in medical imaging.  After the ability to harness these radioactive wavelengths was accomplished, it become possible for chemists and physicists to understand the power behind the energy in which they possessed at their fingertips.  The discovery of the X-ray provided a beginning point for future imaging possibilities in medicine which allows healthcare providers to view the internal environment of the human body in a non-invasive manner.  It was not long until it was discovered how large of an impact the possibilities of imagining technologies could have in the field of medicine.  The advent of imaging techniques that displayed a pictorial representation of the internal environment and condition of the human body eventually led to technologies that allow for numerical measures of internal human dynamics, such as electrocardigrams (ECG), blood pressure monitoring, pulse oximetry, and Bispectral Index monitoring (BIS monitor).   

 


 

Discovery of X-Rays

Wilhelm Roentgen began his educational career in a manner unbecoming of a dedicated student, but disciplined himself to obtain a degree in mechanical engineering followed by a doctorate one year later [1].  His dedication towards his work led him to the development and discovery of wavelengths of radioactive material that were similar to modern X-rays.  The discovery began with him working meticulously with cathode rays in his laboratory he filled one tube with air, added unknown quantity of gas, and passed an electrical current through it [10].  After ensuring that light could not escape, the electrical current was introduced into the gas filled tube.  To Wilhelm's surprise, he noticed a fluorescent ambiance coming from a cardboard screen when placed close to the apparatus [9].  Wilhelm decided that the results and his theories on this newly discovered wave emission need to be reproduced.  On November 8, 1895, he constructed an apparatus similar to the one he previously used.  The experiment began with him covering the gas filled tube with cardboard and turned down the lights to ensure no light would pass through.  Once the lights were down, the electrical current was applied to the tube, and Wilhelm noticed a flickering light coming from the same screen used earlier coming from across the room [11].  This original screen was painted with a substance named Barium platinocyanide, which was the target for the emission of the invisible rays which Wilhelm had stumbled upon [9].  Wilhelm named these new invisible rays "X-rays" allowing "X" to be denote the unknown nature of these waves [10]. 

 

The science behind these newly discovered rays quickly began to catch up to their seemingly accidental discovery.  Modern understanding of the X-ray explains that electrons involved in the process of producing X-rays obtain kinetic energy (KE) or "energy possessed by an object by virtue of its motion" [3]. The cathode rays which Wilhelm previously used allowed for these electrons to create a beam that may strike an object, outline it, and possibly absorb into the targeted material.  When the electrons strike the target, their velocity is changed as they pass by a positively charged nucleus, and as a result they emit radiation waves in the form of photons [5].  The scientific term for this process comes from the German word Bremsstrhlung (braking radiation) [12].  These rays of radiation, which are emitted through this process, provided the effects of the X-ray from an atomic view that is invisible to the naked eye.  The study of these processes allowed for science to quantitatively measure the energy needed for these reactions, and the energy that would be emitted from these reactions.  The importance of quantifying these energy expenditures allowed future medical use of X-rays to adapt energy needed for the different tissues of the body, because different body tissues absorb X-rays differently from one another [5].

 

                                                                                                                   -This captions demonstrates the function of the cathode tube, and the ability                                                                                                                         to capture an electron beam and produce an X-ray.

                                                                    

-Representation of the fluorescent glow produced by cathode

tubes similar to those used by Wilhelm Roentgen.    

 


 

Development of the First Medical Imaging 

 

Wilhelm Conrad Roentgen had discovered rays which possessed the ability to pass through objects and capture images that no one during this time era would have ever imagined possible.  One month after his initially discovery of the fluorescent glow of the Barium plantinocyanide screen, he captured the first X-ray the world had ever seen using his wife as the first photograph [10].  Wilhelm discovered that the X-rays had the ability to capture more than he had even originally believed possible.  Using the same apparatus from his initial experiment, Wilhelm produced an image of the bones of his wife's hand, and the ring that wrapped around her ring finger [1].

                                                                                                                                        -Early X-ray procedure for the internal imaging of an infant.

                                                                                                     

"I have seen my death." -Wilhelm's wife after viewing

the first X-ray of her hand [9]                           

 

This milestone of medical imaging set the stage for future technologies that proceeded.  The first X-ray of Wilhelm's wife's hand attracted the interest of medical professionals during the late 19th and early 20th century.  Wilhelm presented his image to the Wurburg Physical and Medical Society in 1986 which guided the path for the introduction of the X-ray into the world of medicine.  Soon after this publication, aided by these newly developed rays, a doctor in Germany diagnosed sarcoma (malignant tumor of connective tissue [3]) of the tibia of a young boy, and the military implemented X-rays in the location of bullet fragments in soldiers [1].  The quotation from the introductory photograph of this piece denotes the importance of the X-ray  in the world of medicines, for the practice of physicians, and in the outcomes of patient conditions.  X-rays allowed surgeons and physicians to have physical evidence of the internal condition of the human body without needing to unnecessarily open the body to view the internal condition.  These implications also provided useful in the medical training programs across the world.  The first training programs for medicine relied on the ancient teachings of Hippocrates, based solely on what one man believed to be true of the human body.  This was the basis for teaching anatomy to medical students until a law was passed in 1831 that provided medical schools with cadavers for the use of teaching [13].  The birth of X-ray technology provided an even greater means of teaching anatomy in a non-invasive manner.

 

The impact that X-rays have had on medical imaging is extensive, and has allowed for better patient outcomes and quicker, safer diagnostic measures.  Early cathode rays were replaced with large machines that used the same basic principles that the early gas-filled tubes used during the discovery of the unknown, invisible rays.  Dense tissues such as bones, teeth, and tumors provided great targets for absorption from electrons, and provide the emission of radiation based on the Bremsstrhlung Principle [12].  The ability to create images of hollow organs was developed through the use of basic ideas presented by Wilhelm Roentgen.  Scientists and physicians adopted Wilhelm's theories by introducing a radiopaque substance, such as Barium sulfate, which would absorb the X-ray emission [7].  This Barium based material allows for an easy route of entry into the subject's body, and essentially acts as a magnet for the X-rays subjected to the target area.  Modern use of Barium sulfate is similar to the Barium platinocyanide used on the cardboard screen that led to the discovery of the invisible rays that Wilhelm had once described.

 


 

Additional Imaging Technologies

 

                                                                               -The second oldest method of imaging, the Ultrasound (US), showing fetal detail in utero.

                                               

-CT Scan showing a left hemisphere ischemic stroke.                                                      

 

After the discovery of X-rays, and the ability to harness the potential of the kinetic energy produced by the electron beams, newer technologies continued to arise. Computerized Tomography (CT) scans took X-ray imaging to the next step in medical imaging.  The first application of the CT scan was introduced in 1971 at Atkinson Morley's Hospital in South London.  At this site, the first subject was a women with a suspected frontal lobe tumor which underwent CT scanning followed by surgical intervention.  The surgeon that operated on her cerebral pathology stated after the procedure that, "it looks exactly like the picture" [2].  After this first image there was still speculation as to whether or not there was any form of coincidence involved in the findings.  Several more CT scans were conducted, and the discovery of iodine-based contrast media showed advantageous for greater contrast of tumor visualization on CT imaging results [2].  It was not long before the CT scan made its way over seas and become introduced into American medical imaging.  The results of CT scans produce their imaging by exposing the subject to a low emission intensity X-ray located on one side of the subject, which passes through the targeted area to a detector on the opposite side [7].  The X-ray tube emits the electron beam, and produces the radiation necessary for adequate imaging.  On the opposite side of the X-ray tube the detectors provide an area of absorption for the rays, and provide the source which attracts the electrons.  As the X-ray detectors rotate around the targeted area, the subject is moved insidiously through the tube creating three-dimensional slices of the targeted area [6].  This improvement provides a sequences of images of internal tissues and structures from multiple angles as opposed to the previously superior, single-angled, stationary X-ray.  The CT scan allowed for the visualization of internal structures in greater detail, in a relatively short amount of time, and are excellent for producing images of internal hemorrhage due to the iron component of the subject's blood [4].

 

-This diagram represents the the structure of the CT scanner, as well as the process regarding exposure of X-rays to the subject. 

 

Of the older imaging technologies, the X-ray does not stand alone.  The second oldest imaging technology, the Ultrasound (US), provides its imaging capabilities through the use of high-frequency ultrasound waves that penetrate the surface of the human body, strikes the targeted area, and reflects the waves back to the detector producing an image [7].  The image above shows that the contrast and detail of the ultrasound is not as crisp and clear as the CT scan, but it does provide another option for non-invasive imaging in a relatively short amount of time.  This technology has further progressed in medical imaging through the development of echocardiograms (either transthoracic or transesophageal) which allow for a quick assessment of cardiac structure and blood flow in emergent situations [14]. Echocardiolography from US imaging allows for rapid assessment of emergent internal conditions (aortic dissection) that provides the patient with rapid assessment and intervention, as well as improved patient outcomes. The images produced from the use of US technology have become the standard for early assessment of the human fetus in utero.  Images produced during fetal US imaging provides information regarding fetal presentation, possible diagnosis of malformations present, and the possible sex of the fetus.  Compared to The X-ray and CT scan, US imaging less expensive and has greater portability, bringing the imaging source directly to the subject instead of the opposition [4].


 

Magnetic Resonance Imaging and Positron Emission Tomography

 

                        -PET scans of a normal brain compared to a brain displaying mild cognitive impairment and that of a subject with Alzheimer's disease.

                                   

-MRI imaging of the right medial aspect of the knee.                                                                                                                                                                                      

After the establishment of the X-ray, and proceeding CT scanning technology, there were two more imaging technologies which arose which instantly became medical imaging milestones: Magnetic Resonance Imaging (MRI) and Positron Emission Tomography (PET Scan).  MRI imaging was introduced in the medical field in the 1980's, and was based on the theory of atoms behaving in manner similar to a magnet that is set in rotation [6].  As the subject is exposed to the magnetic field produced from the MRI machine (which is roughly 3,000-60,000 times that of the earth's gravitational pull) hydrogen atoms begin to absorb the magnetic energy causing them the become aligned in a linear fashion [7].  The introduction of radio-frequency pulses from the radiology technician will result in the disruption of the linear display of the hydrogen ions exposed to one of three different spatial axes if the ions are turned on to the specific magnetic frequency.  When the linear alignment of the hydrogen ions is disrupted, a resultant emission of energy produced from this reaction necessary for the product of imaging obtained through the precise manipulation of the MRI's magnetic field gradient [7].  This precise process of manipulating hydrogen ions in targeted aspects of the subject's body provides imaging of greater detail.  The above image taken with an MRI of a patient's knee shows great detail in bone structure, muscle condition and positioning, ligament integrity, soft tissue density, as well as precise spacing of joints and the presence of abnormally occurring pathology which may or may not be present.  There is no question that MRI's produce quality imaging which aides in the health care provider's ability to accurately determine and implement needed interventions in the safest manner, but the MRI produce two disadvantages in medical imaging of the modern era.  The first disadvantage of the MRI is the length of time needed for a quality image to be obtained, making this imaging technique unsuitable for emergent situations and patient conditions (as with the example of the internal hemorrhaging patient earlier discussed with the CT scan) [4].  Lastly, the MRI machine itself is constructed as a tube shaped-apparatus in which the patient must be submerged in for the entire length of the procedure (depending on the targeted area of imaging).  This introduces concern when imaging is required for a subject with severe claustrophobia or one which is neurologically impaired (i.e. an individual with dementia), and may require the assistance of a sedative medication for cooperation during the imaging procedure [14].

 

The PET Scan was introduced in the 1970's, and provided physiological imaging of a different aspect.  This imaging technology uses positron emitting isotopes, which is usually a radioactive glucose, to produce a chemical reaction causing the unstable isotope to decay and as a result emit two separate positrons which move in complete opposite directions, and only registers the image captured if two detectors on either side of the target 180 degrees apart react at the same time [6].  Before one can truly understand the the physics behind this technology, one must first understand the terminology.  The positrons which are emitted from the reaction previously described are essentially particles with a positive charge which are similar to electrons.  When these particles collide with electrons they emit gamma rays (usually at roughly 0.511 MeV) which are the basis of the previously described emissions detectable on the PET scanner [7][8].  The above image of an example of a PET scans shows the much different appearance in this type of imaging compared with that of the images produced from X-ray and magnetic technology respectively.  PET imaging provides information regarding cerebral blood flow (in the case of the brain) as well as which target tissues are processing the injected glucose, or essentially which of the targeted tissues are active during the scan [6][7].  The image of the PET scan representing a normal human brain compared to that of one with mild cognitive dysfunction and Alzheimer's disease respectively, provides information regarding the activity level of the cerebral tissues and their ability to metabolize and use glucose.  Darkened areas represented in the brain subjected to Alzheimer's disease show the extent and magnitude of the areas of the brain which are not functioning metabolically in a manner consistent with cerebral homeostasis or normal cognitive functioning.  It is no surprise that the PET scan was initially developed to visualize the brain, and studies may be conducted using music as a stimulus providing the PET scan with different areas of activity in which to record based solely on the type of music played, along with the response of the cerebral cortex [8].

 


 

Numerical Imagining Based on Internal Human Conditions

 

                                                   

-Electrocardiogram (ECG) provides a record of the heart's conduction system from external measurement [14].

 

After the discovery of the X-ray, and the proceeding imaging techniques that followed, new doors opened for medical imaging which took on a different form than a copied image of the human body's internal structures or activity.  The images provided from X-rays, CT, MRI, and Ultrasound imaging provided a medium for the viewer which displayed the internal structure and condition of the targeted tissue under observations, whereas the PET scan provided the functional ability of the targeted tissue under study.  Upon introduction of the Electrocardiogram (ECG) into clinical practice, physicians and clinicians are able to assess the electrical conduction system that keeps the heart pumping in rhythmic fashion.  The figure above provides a diagram of the conduction pathways of the electrical activity of the hear, and their correspondence to the waveform which is created on the monitoring unit.  Initially, the SA node (or the pacemaker of the heart) fires representing depolarization (i.e. contraction) of the atria (i.e. top two chambers of the heart).  This is represented by the "P" wave which begins the waveform activity.  Through pathways inside of the heart, the electrical current travels to the next junction called the AV node.  This node acts as a gatekeeper deciding if an impulse will pass to the ventricles (i.e. bottom two chambers of the heart).  If conduction occurs, the ventricles depolarize, while the atria re-polarize (i.e. relax) [7].  this phase of cardiac conduction is represented as the larger "QRS complex" noted above.  After the ventricles have depolarized, a "T" wave is seen which represents the re-polarization of the ventricles.  Abnormalities of the heart's conduction system may be noted based on changes in ECG waveform from previously established baselines for the patient.  This form of imaging not only provides basis for assessment of electrical conduction system, but may also show changes which represent damage done to the structure of the heart.  An example of this assessment occurs when there is an elevation in the "ST segment," or segment between the "S" portion of the "QRS" and the "T" wave.  This change in imaging represents infarction of the blood supply to a portion of the myocardium [14].

 

-Pulse Oximeter, which is used to measure the status of the blood oxygen levels of the subject [14]

 

Pulse oximetry is another example of modern era medical techniques used to create an image of what the internal conditions of the human body will not allow the naked eye to see.  The probe, which is usually placed on the finger, obtains readings by passing a light through the tissue to a receiver which processes the information.  The information that is obtained via measurement represents the percentage of hemoglobin sites bound with oxygen in comparison to the number of available oxygen binding sites, with a normal value being greater than 95% [3][14].  As shown above, pulse oximetry obtains measurements in a non-invasive, simplistic manner which causes no discomfort to the subject.  The pulse oximeter provides a medium for information sharing which allows physicians and health care providers to obtain the internal oxygen status on their patients in an extremely quick manner.

 

                                                               

-The Bispectral Index (BIS) Monitor.

 

The last aspect of modern day medical imaging that this piece will cover is an extension to the use of Electroencephalograms (EEG), and is a newer technology: The Bispectral Index (BIS) Monitor.  Realization of the effects of anesthetics during surgery has been on the mind's of anesthesiologist since 1939, and EEG readings provided measurements of the effects of these agents on brain activity [15].  As anesthetics depress the Central Nervous System (CNS), they produce a state of hypnosis in the subject which provides a great atmosphere for surgical intervention.  The level of anesthesia the patient reaches with the use of a predetermined amount of a given anesthetic, was once based solely on the determined dosage ranges found in past patient responses to the same agents, followed by introduction of noxious stimuli.  The newly invented imaging of the BIS monitor allows the clinician to map out the brains electrical activity while providing an anesthetic, and allows them to essentially titrate the amount of anesthetic administered without giving too little and risking awareness, or giving too much and risking further depression of the cerebral medulla resulting in a possible comatose state and death.  The images above represent the external lead placement for this monitor, as well as an image of the monitor itself.  On the screen of the monitor, the clinician can view a waveform which represents the brain's electrical activity while under anesthesia, and during the surgical procedure.  Below is a link to a video for brief explanation of the BIS monitor, as well as a chart displaying the numeric value representing the level in which the the cerebral cortex and cerebral medulla have been suppressed due to the anesthetic given.

 

 

        

-This graph represents the various numerical readings for the BIS monitor, and the depth in which the cerebral cortex and cerebral medulla is suppressed.

 


Implications in Media Ecology

 

Media ecology attempts to examine the manner in which forms of communication have evolved over time, and the implications in which technology has contributed to not only the manner in which humans communicate, but as the manner in which humans are changed through the use of technology.  One element in the study of media ecology that this piece revolves around is the theory of signs and symbols.  This theory denotes the distinct difference between a sign (a communication device bounded by action) and a symbol (a communication device that allows a given object or concept to represent or essentially stand for something else) [16].  The concepts that are embedded in the study of the meaning behind signs and symbolism helps to provide framework for the basis of the study of early communication development, and the progression of communication techniques.  The first medical imaging technique, the X-ray, represents the use of a sign for communication.  Likewise the CT, MRI, and Ultrasound provide direct images of the underlying structures of the human body.  These images do not physically stand for something else, but they are exact images of the internal conditions.  From a standpoint of media ecology, the images obtained would essentially be denoted as a symbol with the rationale being that these images are not the actual internal structure, but they instead stand for what is seen internally.  For the purpose of this comparison, these images will instead represents signs.  As medical imaging progressed, as with the progression of communication techniques, the development of symbolism allowed for additional advanced imaging techniques.  The use of the ECG, Pulse Oximeter, and BIS Monitor represent physiological symbolism of internal conditions within the human body and are denoted through a numeric value, or a waveform, instead of exact images of the internal structures (i.e. a copy).  Medical Imaging has progressed and developed from a simple photograph of the internal integrity of the human body, to a form of communication based on symbolism possessing physiologic meaning based on images produced that are polar opposite to the physical appearance of the internal body.

 

 Just as the study of media ecology finds interest in the progression of communication, and how technologies of communication have changed humans, the same interests lies in the hands of physicians and clinicians alike.  There is no doubt that the medical imaging techniques that humans possess today have changed the manner in which healthcare providers practice.  As medical imaging continues to develop into a more superior form, the outcomes for patients all over the world will follow this development as closely as X-rays follow Barium platinocyanide.

 

 

 

 

 

 


References

 

[1] Assmus, A. Early History of X Rays. Beamline, 1995.

[2] Beckmann, E.C. CT scanning in the early days. The British Journal of Radiology, (79), 2006.

[3] Mosby’s Dictionary of Medicine, Nursing, & Health Professions(8th ed.). (2009). St. Louis, MO: Mosby’s, Inc. (2009).

[4] Niederer, P.F. Basic elements of nuclear magnetic resonance for use in medical diagnostics: Magnetic Resonances Imaging (MRI) and Magnetic Resonance Spectroscopy (MRS). Technology and   Health Care. (19). 2011.

[5] Niederer, P. F. Diagnostic Medical Imaging: X-Ray projection technique, image subtraction method, direct digital x-ray imaging, computed tomography (CT). Technology and Health Care. (17), 2009

[6] Purves, D., Augustine, G.J., Fitzpatrick, D., Hall, W.C., LaMantia, A., McNamara, J.O., & White, L.E. Neuroscience Fourth Ed. Sunderland, Mass: Sinauer Associations, 2008

[7] Saldin, K.S. Human Anatomy Second Ed. New York, NY: McGraw-Hill, 2008

[8] Zollman, D., McBride, D., Murphy, S., Aryal, B., & Kalita, S. "Teaching About the Physics of Medical Imaging." International Conference of Physics Education, 2009.

[9] "Wilhelm Rontgen" Wikipedia, The Free Encyclopedia. 29, November 2012, 17:52 UTC. Wikimedia Foundation, Inc. 2012. <http://en.wikipedia.org/wiki/Wilhelm_R%C3%B6ntgen>

[10] NDT The Discovery of X-Rays. <http://www.ndt-ed.org/EducationResources/HighSchool/Radiography/discoveryxrays.htm>

[11] Frame, P.W. Tales from the Atomic Age. Health Physics Society Newsletter. <http://www.orau.org/ptp/articlesstories/invisiblelight.htm>

[12] Britannica Encyclopedia (2012). <http://www.britannica.com/EBchecked/topic/78784/bremsstrahlung>

[13] Perry, J.L., & Kuehn, D.P. "Using Cadavers for Teaching Anatomy of the Speech and Hearing Mechanisms."ASHA (2006)

[14] Lewis, S. L., Dirkensen, S. R., Heitkemper, M. M., Bucher, L., & Camera, I. M. Medical Surgical Nursing Eighth Ed. St. Louis, MO: Mosby's, Inc. (2011).

[15] Bard, J.W. The BIS monitor: a review and technology assessment. American Association of Nurse Anesthetists. 69, (6), 477-483.

[16] Crowley, D. & Heyer, P. Communication in History Sixth Ed. Boston, MA: Pearson Education, Inc., 2011.

 

Comments (3)

Jeff Martinek said

at 11:53 am on Dec 7, 2012

Superb Work, Andrew. One thing you might consider in the "implications" section is the way our ideas about and relationship to our own bodies changed due to these technologies. The "I have seen my death" quote is amazing and speaks to this. The idea of "memento mori" ("you must die") is a familiar motif in art. Usually a skull is included in a painting or even in a play (as in Hamlet) to symbolize the idea of death as the common leveler. So seeing a skeleton always brings along with it this cultural tradition, with all its somber implications. Also, the idea of x-rays becomes part of popular culture --- a power for superheros, a special kind of privileged vision. There used to be ads at the back of comic books selling 'x-ray' glasses, implying it gave teenage boys the power to see underneath clothing. So there is that tradition-----giving us forbidden vision and knowlege of what is supposed to be hid from us. As I said in my email, there is a chapter in Postman's book Technopoloy that goes into some of this. If you have time, it's worth a look. -- JM

Jeff Martinek said

at 4:25 pm on Dec 7, 2012

Go to 16:35 on this:

http://www.youtube.com/watch?v=FWmgJi2Mzg8

You may also be interested in this, which covers the discovery of anesthesia:

http://www.youtube.com/watch?v=OcJHfFiTOqE

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