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Lasers In Urology

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1 hour presentation prepared from an article at emedicine website in AUBMC talking about Laser in urology.
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Lasers In Urology

  1. 1. Lasers in Urology Dr. Ahmad Kharrouby PGY2, Surgery
  2. 2. Laser <ul><li>Laser is an acronym that stands for light amplification by the stimulated emission of radiation </li></ul>
  3. 3. Laser physics <ul><li>Einstein used 2 principles of physics as the basis for his discovery: </li></ul><ul><ul><li>(1) light travels in packets of energy known as photons </li></ul></ul><ul><ul><li>(2) most atoms or molecules exist naturally in a ground or low energy state (E0) </li></ul></ul>
  4. 4. Laser physics <ul><li>By adding electricity, heat, or light energy to atoms in their ground state, their energy level can be raised </li></ul><ul><li>The energy then is released spontaneously in the form of photons or electromagnetic (EM) waves to return to the ground state </li></ul>
  5. 5. The concept of laser <ul><li>When a photon of light energy of a certain wavelength strikes an excited atom (En), that photon and the photon(s) of light that is released are discharged simultaneously and therefore will be identical in frequency and phase </li></ul>
  6. 6. Anatomy of a laser <ul><li>The populations of atoms or molecules that become excited are the lasing medium </li></ul><ul><li>The lasing medium exists between 2 mirrors for light amplification to occur; one is fully reflective and the other only partially reflective </li></ul><ul><li>Once the lasing medium at the core is excited by a pumping mechanism that supplies energy, a population inversion occur </li></ul><ul><li>Some photons are emitted spontaneously from the excited atoms or molecules that cause light to travel in all directions within the laser cavity </li></ul>
  7. 7. Difference between LASER & natural light <ul><li>Coherence (the photons are all in phase) </li></ul><ul><li>Collimation (they travel parallel with no divergence) </li></ul><ul><li>Monochromaticity (they all have the same wavelength and, therefore, the same color if within the visible light spectrum) </li></ul>
  8. 8. Lasing medium <ul><li>Different lasing mediums (which can be either solid, liquid, or gas) emit photons in different wavelengths of the EM spectrum </li></ul>
  9. 9. Factors affecting Laser <ul><li>Other characteristics that affect laser performance are the power output and the mode of emission: </li></ul><ul><ul><li>Continuous wave </li></ul></ul><ul><ul><li>Pulsed (more precise control and less lateral heat conduction to tissues ) </li></ul></ul>
  10. 10. The physical properties of a laser <ul><li>Can be described using 4 key concepts </li></ul><ul><ul><li>Energy describes the amount of work accomplished and is measured in joules </li></ul></ul><ul><ul><li>Power refers to the rate of energy expenditure and is measured in joules per second, or watts (1 J/s = 1 W </li></ul></ul><ul><ul><li>The fluence, describes the amount of energy delivered per unit area (J/cm2) </li></ul></ul><ul><ul><li>Irradiance is a term used to describe the intensity of a laser beam, and it is measured in watts per square centimeter </li></ul></ul>
  11. 11. Pathophysiology
  12. 12. The biophysics of laser-tissue interactions <ul><li>Factors affecting laser-tissue interactions: </li></ul><ul><ul><li>Local tissue properties </li></ul></ul><ul><ul><li>Local blood circulation </li></ul></ul><ul><ul><li>Laser: </li></ul></ul><ul><ul><ul><li>wavelength </li></ul></ul></ul><ul><ul><ul><li>Energy </li></ul></ul></ul><ul><ul><ul><li>mode </li></ul></ul></ul>
  13. 13. The biophysics of laser-tissue interactions <ul><li>Molecules, proteins, and pigments may absorb light only in a specific range of wavelengths </li></ul>
  14. 14. The biophysics of laser-tissue interactions <ul><li>The wavelength of laser light can be proportional to the depth of penetration into specific tissues </li></ul><ul><li>The longer the wavelength, the deeper the expected penetration </li></ul>
  15. 15. The biophysics of laser-tissue interactions <ul><li>Surgeons currently using lasers seek 4 different effects— </li></ul><ul><ul><li>Thermal </li></ul></ul><ul><ul><li>Mechanical </li></ul></ul><ul><ul><li>Photochemical </li></ul></ul><ul><ul><li>tissue welding effects </li></ul></ul>
  16. 16. The biophysics of laser-tissue interactions <ul><li>The most common utilization is the thermal effect, whereby light energy is absorbed and transformed into heat </li></ul>
  17. 17. The biophysics of laser-tissue interactions <ul><li>The mechanical effect results, for example, when a very high power density is directed at a urinary calculus </li></ul><ul><li>This creates a plasma bubble that swiftly expands and acts like a sonic boom to disrupt the stone along stress lines </li></ul>
  18. 18. The biophysics of laser-tissue interactions <ul><li>The photochemical effect refers to the selective activation of a specific drug or molecule, which may be administered systemically but is taken up in selected tissues </li></ul>
  19. 19. The biophysics of laser-tissue interactions <ul><li>Finally, the tissue-welding effect is derived by focusing light of a particular wavelength to induce collagen cross-linking </li></ul>
  20. 20. Laser types and clinical applications
  21. 21. Ruby laser <ul><li>The laser produces red light at a wavelength of 694 nm </li></ul><ul><li>The ruby laser is less efficient than more modern lasing materials </li></ul><ul><li>Used in a for removal of pigmented lesions and tattoos, with little scarring </li></ul>
  22. 22. CO2 laser <ul><li>The CO2 laser emits in the invisible far infrared portion of the EM spectrum, at 10,600 nm </li></ul><ul><li>It usually is coupled with a visible helium-neon beam for guidance </li></ul><ul><li>Its beam is highly absorbed by water </li></ul><ul><li>Therefore, it vaporizes water-dense tissues to a superficial depth of less than 1 mm </li></ul>
  23. 23. Neodymium:yttrium-aluminum-garnet laser <ul><li>ND:YAG is used commonly today because of its efficiency </li></ul><ul><li>The Nd:YAG laser emits a beam at 1064 nm (near infrared) </li></ul><ul><li>Deep penetration of as much as 10 mm because this frequency is outside the absorption peaks of both hemoglobin and water </li></ul><ul><li>It has good hemostatic (coagulates blood vessels as much as 5 mm in diameter) and cutting properties and also is suitable for lithotripsy </li></ul>
  24. 24. Potassium-titanyl phosphate crystal laser <ul><li>(KTP) laser, yields a green visible light beam of 532 </li></ul><ul><li>It is used for incisions, resection, and ablation </li></ul>
  25. 25. Alexandrite laser <ul><li>This is a tunable laser </li></ul><ul><li>The wavelength range is from 380-830 nm </li></ul><ul><li>This light is absorbed well by melanin; therefore, it can be used for cutaneous lesions </li></ul><ul><li>It is used for lithotripsy of pigmented stone </li></ul><ul><li>This laser also can be used for tissue welding </li></ul>
  26. 26. Semiconductor diode laser <ul><li>Smaller, more efficient, and potentially cheaper than most other lasers now in use </li></ul><ul><li>Their wavelength can be tuned </li></ul><ul><li>These lasers currently are used for tissue coagulation and thermal treatment of solid organs, including the prostate </li></ul>
  27. 27. Holmium:YAG laser <ul><li>Holmium:YAG (Ho:YAG) is a somewhat recent edition </li></ul><ul><li>It consists of the rare earth element holmium, doped in a YAG crystal that emits a beam of 2150 nm </li></ul><ul><li>This laser energy is delivered most commonly in a pulsatile manner </li></ul><ul><li>It superheats water, which heavily absorbs light energy at this wavelength </li></ul><ul><li>This creates a vaporization bubble at the probe </li></ul><ul><li>This vapor bubble expands rapidly and destabilizes the molecules it contacts </li></ul><ul><li>It is ideal for lithotripsy of all stone types </li></ul><ul><li>The absorption depth in tissue is 1-2 mm, as long as it is used in a water-based medium </li></ul><ul><li>This specific light energy provides good hemostasis when used in a pulsed mode of 250 ms duration and at low pulse repetition rate </li></ul><ul><li>It also may be used for incisions at higher repetition rates </li></ul>
  28. 28. Nitrogen laser <ul><li>It emits light with a wavelength of 337 nm </li></ul><ul><li>Used as a diagnostic test for transitional cell carcinoma (TCC) and other mucosal malignancies i.e. autofluorescence </li></ul>
  29. 29. Current laser applications
  30. 30. Urolithiasis <ul><li>Lasers are ideally suited for either retrograde ureteroscopy or percutaneous nephrostolithotomy </li></ul><ul><li>Laser lithotripsy first was used clinically in the late 1980s, using the coumarin-based pulsed dye laser </li></ul><ul><li>The mechanism of action occurs via plasma formation between the fiber tip and the calculus, which develops an acoustic shock wave that disrupts the stone along fracture lines </li></ul>
  31. 31. Urolithiasis <ul><li>The Ho:YAG is the best nowadays </li></ul><ul><li>Allow for segmental resection of all stones, regardless of their composition </li></ul><ul><li>Accurate fiber contact against a calculus is the primary safety factor </li></ul>
  32. 32. Laser therapy for benign prostatic hyperplasia <ul><li>Laser prostatectomy </li></ul><ul><li>The 2 main tissue effects are </li></ul><ul><ul><li>coagulation </li></ul></ul><ul><ul><li>vaporization </li></ul></ul>
  33. 33. Laser therapy for benign prostatic hyperplasia <ul><li>Coagulation occurs when somewhat diffusely focused laser energy heats tissue to 100°C </li></ul><ul><li>Proteins denature, and necrosis ensues </li></ul><ul><li>This results in subsequent sloughing of necrotic tissue </li></ul><ul><li>This process often initially results in edema, which increases prostate volume transiently (may require short-term Foley) </li></ul>
  34. 34. Laser therapy for benign prostatic hyperplasia <ul><li>Vaporization occurs when greater laser energy is focused (increased power density) and tissue temperatures reach as high as 300°C </li></ul><ul><li>This causes tissue water to vaporize and results in an instantaneous debulking of prostatic tissue </li></ul>
  35. 35. Laser therapy for benign prostatic hyperplasia <ul><li>The high-power (80 W) potassium-titanyl phosphate laser (KTP, or Greenlight) is commonly used for its vaporization effects </li></ul><ul><li>This procedure is associated with significantly less bleeding and fluid absorption than standard TURP </li></ul><ul><li>The KTP procedure is a safe and effective treatment option in seriously ill patients or those receiving oral anticoagulants </li></ul><ul><li>Drawbacks to the KTP procedure include the lack of tissue obtained for postoperative pathological analysis and the inability to diagnose and unroof concomitant prostatic abscesses </li></ul>
  36. 36. Laser therapy for benign prostatic hyperplasia <ul><li>Nd:YAG is used most commonly for its coagulative effect </li></ul><ul><li>The procedure is termed visual laser ablation of the prostate (VLAP) </li></ul><ul><li>Typically, segmental coagulation is achieved by aiming for the 12, 3, 6, and 9 o'clock positions </li></ul><ul><li>The postoperative course may be complicated by irritative voiding symptoms because of the disrupted urethral epithelium </li></ul>
  37. 37. Laser therapy for benign prostatic hyperplasia <ul><li>The Ho:YAG laser have been used to incise or enucleate prostate adenomas down to the capsule </li></ul><ul><li>The Ho:YAG is ideally suited for this task because it creates precise incisions, cuts by vaporizing tissue with adequate hemostasis, and leaves minimal collateral damage </li></ul><ul><li>Advantages of this method include the availability of a specimen for histologic examination, less postoperative catheter time, and the ability to excise large adenomas </li></ul>
  38. 38. Laser therapy for benign prostatic hyperplasia <ul><li>Laser modalities are safer than TURP in the perioperative period (less bleeding & shorter hospital stay), although some may have a similar long-term complication profile </li></ul>
  39. 39. Laser treatment of urothelial malignancies <ul><li>Most commonly, holmium and Nd:YAG are used in this setting </li></ul><ul><ul><li>The Nd:YAG laser energy is used to coagulate and ablate with a thermal effect </li></ul></ul><ul><ul><li>Holmium is more precise, with less of a coagulative effect </li></ul></ul>
  40. 40. Laser treatment of urothelial malignancies <ul><li>Advantages </li></ul><ul><ul><li>less bleeding; consequently, catheter drainage usually is not needed </li></ul></ul><ul><ul><li>a lower incidence of stricture formation </li></ul></ul><ul><ul><li>decreased need for anesthesia,& less postoperative pain </li></ul></ul><ul><ul><li>can be used in an office setting </li></ul></ul><ul><li>Disadvantages </li></ul><ul><ul><li>no pathology specimen is available, obtain multiple prior biopsy samples </li></ul></ul><ul><ul><li>the area of destruction is deep and not fully visualized </li></ul></ul><ul><ul><li>Some reports of bowel perforation exist </li></ul></ul>
  41. 41. Laser treatment of urothelial malignancies <ul><li>Photodynamic therapy is another form of tumor ablation where a systemically administered compound is absorbed or retained preferentially by cancer cells and converted by laser light to a toxic compound </li></ul><ul><li>This compound usually acts through oxygen radicals to destroy malignant cells </li></ul><ul><li>Lasers are suited ideally for this form of therapy </li></ul><ul><li>This is especially promising for TCC–carcinoma in situ (CIS), which shows complete responses </li></ul>
  42. 42. Lasers for urothelial stricture disease <ul><li>Nd:YAG, KTP, and Ho:YAG lasers all have been used experimentally to vaporize fibrous strictures </li></ul><ul><li>They can have rates of recurrence similar to the cold-knife internal urethrotomy </li></ul><ul><li>Ureteropelvic junction obstructions, posterior urethral valves, and even bladder neck contractures recently have been treated using laser energy </li></ul><ul><li>Ho:YAG is most likely the best form of laser energy for these tasks </li></ul><ul><li>Ureteroscopic laser endopyelotomy is a minimally invasive, short-stay outpatient procedure associated with 73.1 % success rate </li></ul>
  43. 43. Lasers for the ablation of skin lesions <ul><li>Lasers offer minimal scarring and superior cosmetic results when compared with other forms of cutaneous lesion resection </li></ul><ul><ul><li>Condyloma acuminata </li></ul></ul><ul><ul><li>Penile carcinoma in the early stages (eg, CIS, T1 or T2) </li></ul></ul><ul><ul><li>Cutaneous hemangiomas (highly indicated) </li></ul></ul>
  44. 44. FUTURE AND CONTROVERSIES
  45. 45. <ul><li>Laser energy is applied in a constructive manner to reapproximate tissues </li></ul><ul><li>The results are very promising thus far, with good tensile strength, watertight seals, and minimal scar formation </li></ul><ul><li>Tissue solders (albumin solutions) and chromophores added to tissue edges before reapproximation speed the welding process, increase tensile strength, and minimize collateral injury </li></ul>
  46. 46. <ul><li>This technology may be particularly helpful in laparoscopic surgery </li></ul><ul><li>Uses </li></ul><ul><ul><li>Vasovasotomy for vasectomy </li></ul></ul><ul><ul><li>Hypospadias repair </li></ul></ul><ul><ul><li>Pyeloplasty </li></ul></ul><ul><ul><li>augmentation cystoplasty </li></ul></ul><ul><ul><li>continent urinary diversion. Proposed future </li></ul></ul><ul><ul><li>laparoscopic ureteroureterostomy </li></ul></ul><ul><ul><li>laparoscopic Pyeloplasty </li></ul></ul><ul><ul><li>laparoscopic Ureteroneocystostomy </li></ul></ul><ul><ul><li>laparoscopic bladder and bowel anastomoses </li></ul></ul><ul><li>Because urine lacks the clotting ability of blood, tight anastomoses of urothelial structures are even more important than in vascular surgery </li></ul>
  47. 47. Autofluorescence <ul><li>Light of 337 nm emitted by a nitrogen laser and applied to bladder tissue can Identify Malignant tissue </li></ul><ul><li>This method of detection has yielded a very high sensitivity, specificity, and positive and negative predictive values, (97, 98, 93, and 99% respectively) </li></ul>
  48. 48. References <ul><li>Prepared from emedicine website </li></ul>
  49. 49. Thank You

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