Jumat, 18 Maret 2011

Nuclear medicine

Nuclear medicine is a branch or specialty of medicine and medical imagingthat uses radionuclides and relies on the process of radioactive decay in the diagnosis and treatment of disease.


In nuclear medicine procedures, elemental radionuclides are combined with other elements to form chemical compounds, or else combined with existingpharmaceutical compounds, to form radiopharmaceuticals. These radiopharmaceuticals, once administered to the patient, can localize to specific organs or cellular receptors. This property of radiopharmaceuticals allows nuclear medicine the ability to image the extent of a disease-process in the body, based on the cellular function and physiology, rather than relying on physical changes in the tissue anatomy. In some diseases nuclear medicine studies can identify medical problems at an earlier stage than other diagnostic tests.

Treatment of diseased tissue, based on metabolism or uptake or binding of a particular ligand, may also be accomplished, similar to other areas of pharmacology. However, the treatment effects of radiopharmaceuticals rely on the tissue-destructive power of short-range ionizing radiation.


Further reading

  • Mas JC: A Patient's Guide to Nuclear Medicine Procedures: English-Spanish. Society of Nuclear Medicine, 2008. ISBN 978-0972647892
  • Taylor A, Schuster DM, Naomi Alazraki N: A Clinicians' Guide to Nuclear Medicine, 2nd edition. Society of Nuclear Medicine, 2000. ISBN 978-0932004727
  • Mark J. Shumate MJ, Kooby DA, Alazraki NP: A Clinician's Guide to Nuclear Oncology: Practical Molecular Imaging and Radionuclide Therapies. Society of Nuclear Medicine, January 2007. ISBN 978-0972647885
  • Ell P, Gambhir S: Nuclear Medicine in Clinical Diagnosis and Treatment. Churchill Livingstone, 2004. (1950 pages) ISBN 978-0443073120
External links
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Jumat, 18 Februari 2011

Photomedicine

Photomedicine is an interdisciplinary branch of medicine that involves the study and application of light with respect to health and disease. Photomedicine may be related to the practice of various fields of medicine including dermatology, surgery, interventional radiology, optical diagnostics, cardiology, and oncology.

A branch of photomedicine is light therapy.


Examples

See also

External links

Journals and Societies

Miscellaneous
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Selasa, 18 Januari 2011

Interventional radiology

Interventional radiology (abbreviated IR or sometimes VIR for vascular and interventional radiology, also known as Image-Guided Surgery or Surgical Radiology) is a subspecialty of radiology, or in Europe a separate subspecialty of medicine in its own right, in which minimally invasive procedures are performed using image guidance. Some of these procedures are done for purely diagnostic purposes (e.g., angiogram), while others are done for treatment purposes (e.g., angioplasty).

The basic concept behind interventional radiology is to diagnose or treat pathology with the most minimally invasive technique possible. Images are used to direct interventional procedures, which are usually done with needles and narrow tubes called catheters. The images provide road maps that allow the interventional radiologist to guide these instruments through the body to the areas containing disease. By minimizing the physical trauma to the patient, peripheral interventions can reduce infection rates and recovery time as well as shorten hospital stays.[1]

History

The advancements in the field of radiological imaging such as the Seldinger technique, together with innovations in instrumentation, led to a rapid development in interventional procedures in the 1970s.Cardiovascular procedures were found to be particularly well-suited for guided and minimally invasive operations, and catheterization remains as one of the main applications for interventional radiology.

Nobel nominee Charles Dotter is considered the "father of angioplasty and interventional radiology".[2]

See also: Interventional cardiology


Training

As in most medical specialties, training varies depending on varying rules and regulations from country to country. In the United States, interventional radiologists are physicians whose education and training traditionally includes completing a college degree, four years of medical school, a year of training in general medicine and/or surgery (internship), a four year diagnostic radiology residency program, and then a one or two year fellowship in vascular & interventional radiology. Alternative pathways exist.


Imaging Modalities

Common interventional imaging modalities include fluoroscopy, computed tomography (CT), ultrasound (US), and magnetic resonance imaging (MRI). Fluoroscopy and computed tomography use ionizing radiation that may be potentially harmful to the patient and the interventional radiologist. However, both methods have the advantages of being fast and geometrically accurate. Ultrasound suffers from image quality and tissue contrast problems, but is also fast and inexpensive. Magnetic resonance imaging provides superior tissue contrast, at the cost of being expensive and requiring specialized instruments that will not interact with the magnetic fields present in the imaging volume.


Procedures

Common IR procedures are:

  • Angiography: imaging the blood vessels to look for abnormalities with the use of various contrast media, including iodinated contrast, gadolinium based agents, and CO2 gas.
  • Chemoembolization: delivering cancer treatment directly to a tumour through its blood supply, then using clot-inducing substances to block the artery, ensuring that the delivered chemotherapy is not "washed out" by continued blood flow.
  • Cholecystostomy: placement of a tube into the gallbladder to remove infected bile in patients with cholecystitis, an inflammation of the gallbladder, who are too frail or too sick to undergo surgery
  • Drain insertions: placement of tubes into different parts of the body to drain fluids (e.g., abscess drains to remove pus, pleural drains)
  • Embolization: blocking abnormal blood (artery) vessels (e.g., for the purpose of stopping bleeding) or organs (to stop the extra function e.g. embolization of the spleen for hypersplenism) including uterine artery embolization for percutaneous treatment of uterine fibroids. Various embolic agents are used, including alcohol, glue, metallic coils, poly-viny alcohol particles, Embospheres, encapsulated chemo-microsphere, and gelfoam.
  • Thrombolysis: treatment aimed at dissolving blood clots (e.g., pulmonary emboli, leg vein thrombi, thrombosed hemodialysis accesses) with both pharmaceutical (TPA) and mechanical means
  • Biopsy: taking of a tissue sample from the area of interest for pathological examination from a percutaneous or transjugular approach
  • IVC filters: - metallic filters placed in the inferior vena cavae to prevent propagation of deep venous thrombus, both temporary and permanent.
Inferior vena cava filter
  • Nephrostomy placement: Placing a catheter directly into the kidney to drain urine in situations where normal flow of urine is obstructed. NUS catheters are nephroureteral stents which are placed through the ureter and into the bladder.
  • Dialysis access and related intervention: Placement of tunneled hemodialysis catheters, peritoneal dialysis catheters, and revision/thrombolysis of poorly functioning surgically placed AV fistulas and grafts.
  • TIPS : Placement of a Transjugular Intrahepatic Porto-systemic Shunt (TIPS) for management of select patients with critical end-stage liver disease and portal hypertension
  • Biliary intervention - Placement of catheters in the biliary system to bypass biliary obstructions and decompress the biliary system. Also placement of permanent indwelling biliary stents.
  • Endovenous laser treatment of varicose veins - Placement of thin laser fiber in varicose veins for non-surgical treatment of venous insufficiency
  • Radioembolization: Embolization of liver with radioactive microspheres of glass or plastic, to kill tumors while minimizing exposure to healthy cells.


Tools

There are a number of catheters used in interventional radiology that can be loosely divided into five types:

  • Diagnostic angiographic catheters
  • Micro catheters
  • Drainage catheters
  • Balloon catheters
  • Central venous catheters


See also


References

  1. ^ Society of Interventional Radiology -- Global Statement Defining Interventional radiology.http://www.sirweb.org/news/newsPDF/IR_Global_Statement.pdf
  2. ^ Lakhan SE, Kaplan A, Laird C, Leiter Y (2009). "The interventionalism of medicine: interventional radiology, cardiology, and neuroradiology". International Archives of Medicine 2 (27): 27. doi:10.1186/1755-7682-2-27. PMC 2745361. PMID 19740425.
  • Rösch J, Keller F, Kaufman J (2003). "The birth, early years, and future of interventional radiology". J Vasc Interv Radiol 14 (7): 841–53. PMID 12847192.


External links

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Sabtu, 18 Desember 2010

Photodynamic Therapy




Close up of surgeons' hands in an operating room with a "beam of light" traveling along fiber optics for photodynamic therapy. Its source is a laser beam which is split at two different stages to create the proper "therapeutic wavelength". A patient would be given a photo sensitive drug (photofrin) containing cancer killing substances which are absorbed by cancer cells. During the surgery, the light beam is positioned at the tumor site, which then activates the drug that kills the cancer cells, thus photodynamic therapy (PDT).

Photodynamic therapy (PDT), matured as a feasible medical technology in the 1980s at several institutions throughout the world, is used to eradicate premalignant and early-stage cancer and reduce the tumour size in end-stage cancers[1] involving three key components: a photosensitizer, light (wavelength appropriate for the photosensitzer), and tissue oxygen. The light causes the photosensitizer to cause the oxygen to damage and kill the tissues exposed to the light.

It is an approved treatment for wet macular degeneration, and is also being investigated for treatment of psoriasis.

Treatment of internal organs may be achieved through the use of endoscopes and fiber optic catheters to deliver light, and intravenously-administered photosensitizers.

A great deal of research and clinical study is now underway to determine optimal combinations of photosensitizers, light sources, and treatment parameters for a wide variety of different cancers.

It is currently being tested as a treatment for severe acne.[2][3][4]
















History

The German physician Friedrich Meyer–Betz performed the first study with what was first called photoradiation therapy (PRT) with porphyrins in humans in 1913. Meyer–Betz tested the effects of haematoporphyrin-PRT on his own skin.[5]

Thomas Dougherty of Roswell Park Cancer Center, among others worldwide, became a highly visible advocate and educator. Early patients were treated at Roswell, Los Angeles Children's Hospital, Los Angeles County Hospital, and other clinics and Hospitals in the USA and overseas.[6]

It was John Toth, as product manager for Cooper Medical Devices Corp/Cooper Lasersonics, who acknowledged the "photodynamic chemical effect" of the therapy with early clinical argon dye lasers and wrote the first "white paper" renaming the therapy as "Photodynamic Therapy" (PDT). This was done to support efforts in setting up 10 clinical sites in Japan where the term "radiation" had negative connotations. PDT received even greater interest as result of Thomas Dougherty helping expand clinical trials and forming theInternational Photodynamic Association, in 1986.

Despite excellent results it is only slowly being adopted in the UK as compared to say Italy - in part due to lack of suitable equipment and training.


Mechanism of action

A photosensitizer is a chemical compound that can be excited by light of a specific wavelength. This excitation uses visible or near-infrared light. In photodynamic therapy, either a photosensitizer or the metabolic precursor of one is administered to the patient. The tissue to be treated is exposed to light suitable for exciting the photosensitizer. Usually, the photosensitizer is excited from a groundsinglet state to an excited singlet state. It then undergoes intersystem crossing to a longer-lived excited triplet state. One of the few chemical species present in tissue with a ground triplet state is molecular oxygen. When the photosensitizer and an oxygen molecule are in proximity, an energy transfer can take place that allows the photosensitizer to relax to its ground singlet state, and create an excited singlet state oxygen molecule. Singlet oxygen is a very aggressive chemical species and will very rapidly react with any nearby biomolecules. (The specific targets depend heavily on the photosensitizer chosen.) Ultimately, these destructive reactions will kill cells through apoptosis or necrosis.

This mechanism is identical to the mechanism of the disease erythropoietic protoporphyria, which causes blistering in response to sun exposure due to a genetic defect in the same metabolic pathway.

Example treatment of skin cancer

As an example, consider PDT as a treatment for basal cell carcinoma (BCC). BCC is the most common form of skin cancer in humans. Conventional treatment of BCC involves surgical excision, cryogenic treatment with liquid nitrogen, or localized chemotherapy with 5-fluorouracil or other agents.

A PDT treatment would involve the following steps.

  • A photosensitizer precursor (aminolevulinic acid (ALA) or methyl aminolevulinate (MAL) or levulinic acid (LA)) is applied.
  • A waiting period of a few hours is allowed to elapse, during which time
  • The physician shines a bright red light (from an array of light-emitting diodes or a diode laser) on the area to be treated. The light exposure lasts a few minutes to a few tens of minutes.
    • Protoporphyrin IX absorbs light, exciting it to an excited singlet state;
    • Intersystem crossing occurs, resulting in excited triplet protoporphyrin IX;
    • Energy is transferred from triplet protoporphyrin IX to triplet oxygen, resulting in singlet (ground state) protoporphyrin IX and excited singlet oxygen;
    • Singlet oxygen reacts with biomolecules, fatally damaging some cells in the treatment area.
  • Within a few days, the exposed skin and carcinoma will scab over and flake away.
  • In a few weeks, the treated area has healed, leaving healthy skin behind. For extensive malignancies, repeat treatments may be required. It is also common to experience pain from the area treated.
  • After the treatment the patient will need to avoid excessive exposure to sunlight for a period of time.


Advantages and limitations

Unlike chemotherapy for cancer the effect of PDT can be localised. Specificity of treatment is achieved in three ways.

  • First, light is delivered only to tissues that a physician wishes to treat. In the absence of light, there is no activation of the photosensitizer and no cell killing.
  • Second, photosensitizers may be administered in ways that restrict their mobility.
  • Finally, photosensitizers may be chosen which are selectively absorbed at a greater rate by targeted cells. ALA is taken up much more rapidly by metabolically active cells. Since malignant cells tend to be growing and dividing much more quickly than healthy cells, the ALA targets the unhealthy cells.

PDT can be much cheaper than the alternative radiotherapy or surgical operation and after care. Post operative recovery is typically hours or days rather than weeks.

A major limitation of PDT is that the light needed to activate most photosensitizers can not penetrate through more than one third of an inch (1 cm) of tissue using standard laser technology and low powered LED technology. Laser application of PDT is generally limited to the treatment of tumours on or under the skin, or on the lining of some internal organs. Moreover it is less effective in treatment of large tumours and metastasis for the same reason. However, new high-powered LED technology has been lab-tested to provide a depth of 2 inches from surface in a simulated breast tissue. Also, hollow needles have been used by some units to get the light into deeper tissues.[7]


Photosensitizers

A wide array of photosensitizers for PDT exist. They can be divided into porphyrins, chlorophylls and dyes.[8] Some examples includeaminolevulinic acid (ALA), Silicon Phthalocyanine Pc 4, m-tetrahydroxyphenylchlorin (mTHPC), and mono-L-aspartyl chlorin e6 (NPe6).

Several photosensitizers are commercially available for clinical use, such as Photofrin, Visudyne, Levulan, Foscan, Metvix, Hexvix®,Cysview™, and Laserphyrin, with others in development, e.g. Antrin, Photochlor, Photosens, Photrex, Lumacan, Cevira, Visonac, BF-200 ALA.[8][9] Amphinex.[10] Also Azadipyrromethenes.

Although these photosensitizers can be used for wildly different treatments, they all aim to achieve certain characteristics[11]:

  • High absorption at long wavelengths
    • Tissue is much more transparent at longer wavelengths (~700-850 nm). Absorbing at longer wavelengths would allow the light to penetrate deeper,[10] and allow the treatment of larger tumors.
  • High singlet oxygen quantum yield
  • Low photobleaching
  • Natural fluorescence
  • High chemical stability
  • Low dark toxicity
    • The photosensitizer should not be harmful to the target tissue until the treatment beam is applied.
  • Preferential uptake in target tissue

The major difference between different types of photosensitizers is in the parts of the cell that they target. Unlike in radiation therapy, where damage is done by targeting cell DNA, most photosensitizers target other cell structures. For example, mTHPC has been shown to localize in the nuclear envelope and do its damage there.[13] In contrast, ALA has been found to localize in the mitochondria[14] andMethylene Blue in the lysosomes.[15]


Targeted PDT

Some photosensitisers naturally accumulate in the endothelial cells of vascular tissue allowing 'vascular targeted' PDT, but there is also research to target the photosensitiser to the tumour (usually by linking it to antibodies or antibody fragments). It is currently only in pre-clinical studies.[16][17] Some photosensitizers in development are linked to antibodies to target them at the tumour cells.

Other research

To allow treatment of deeper tumours some researchers are using internal chemiluminescence to activate the photosensitiser.[18]

PDT is currently in clinical trials to be used as a treatment for severe acne. Initial results show have shown for it to be effective as a treatment only for severe acne,[19] though some question whether it is better than existing acne treatments. The treatment causes severe redness and moderate to severe pain and burning sensation. (see also: Levulan)

See also


References

  1. ^ http://www.clinuvel.com/skin-conditions/photodynamic-therapy-pdt-and-phototoxicity
  2. ^ http://clinicaltrials.gov/ct2/show/NCT00706433?term=photodynamic+therapy+acne&rank=1
  3. ^ Inglis, Leslie (June 23, 2005). "Acne sufferer finally sees the light; Early treatment can reduce scarring".
  4. ^ "Laser therapy combo effectively clears acne, reduces oil production". The Times Of India.
  5. ^ Meyer-Betz, Friedrich (1913). "Untersuchungen uber die Biologische (photodynamische) Wirkung des hamatoporphyrins und anderer Derivative des Blut-und Gallenfarbstoffs.". Dtsch. Arch. Klin. Med. 112: 476–503.
  6. ^ Moan, J.; Q. Peng (2003). "An outline of the history of PDT". In Thierry Patrice. Photodynamic Therapy. Comprehensive Series in Photochemistry and Photobiology. 2. The Royal Society of Chemistry. pp. 1–18. doi:10.1039/9781847551658.
  7. ^ "A Phase 3 Study of Talaporfin Sodium and Interstitial Light Emitting Diodes Treating Hepatocellular Carcinoma (HCC)".ClinicalTrials.gov. Retrieved October 4, 2008.
  8. ^ a b Allison, Ron R; et al. (2004). "Photosensitizers in clinical PDT" (PDF). Photodiagnosis and Photodynamic Therapy (Elsevier) 1: 27–42. doi:10.1016/S1572-1000(04)00007-9.
  9. ^ http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1317568/ "A Review of Progress in Clinical Photodynamic Therapy" 2005
  10. ^ a b O'Connor, Aisling E, Gallagher, William M, Byrne, Annette T (2009). "Porphyrin and Nonporphyrin Photosensitizers in Oncology: Preclinical and Clinical Advances in Photodynamic Therapy. Photochemistry and Photobiology, Sep/Oct 2009". Photochemistry and Photobiology.
  11. ^ Wilson, Brian C; Michael S Patterson (2008). "The physics, biophysics, and technology of photodynamic therapy". Physics in Medicine and Biology 53 (9): R61–R109. doi:10.1088/0031-9155/53/9/R01. PMID 18401068.
  12. ^ Lee, Tammy K; Elma D Baron, Thomas H Foster (2008). "Monitoring Pc4 photodynamic therapy in clinical trials of cutaneous T-cell lymphoma using noninvasive spectroscopy". Journal of Biomedical Optics 13 (3): 030507. doi:10.1117/1.2939068. PMC 2527126.PMID 18601524.
  13. ^ Foster, TH; BD Pearson, S Mitra, CE Bigelow (2005). "Fluorescence anisotropy imaging reveals localization of meso-tetrahydroxyphenyl chlorin in the nuclear envelope.". Photochemistry and Photobiology 81 (6): 1544–1547. doi:10.1562/2005-08-11-RN-646.PMID 16178663.
  14. ^ Wilson, JD; CE Bigelow, DJ Calkins, TH Foster (2005). "Light scattering from intact cells reports oxidative-stress-induced mitochondrial swelling.". Biophysical Journal (Biophysical Society) 88 (4): 2929–2938. doi:10.1529/biophysj.104.054528. PMC 1305387.PMID 15653724.
  15. ^ Mellish, Kirste; Russell Cox, David Vernon, John Griffiths, Stanley Brown (2002). "In Vitro Photodynamic Activity of a Series of Methylene Blue Analogues". Photochemistry and Photobiology (American Society for Photobiology) 75 (4): 392–397. doi:10.1562/0031-8655.PMID 12003129.
  16. ^ http://cat.inist.fr/?aModele=afficheN&cpsidt=18046718 "Synthesis, characterization and preclinical studies of two-photon- activated targeted PDT therapeutic triads" 2006
  17. ^ http://www.ncbi.nlm.nih.gov/pubmed/15249365 "Selective photodynamic therapy by targeted verteporfin delivery to experimental choroidal neovascularization mediated by a homing peptide to vascular endothelial growth factor receptor-2." July 2004
  18. ^ http://www.nature.com/bjc/journal/v95/n2/full/6603241a.html "Intracellular chemiluminescence activates targeted photodynamic destruction of leukaemic cells" 2006
  19. ^ http://clinicaltrials.gov/ct2/show/NCT00706433?term=photodynamic+therapy&cond=acne&rank=1


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