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Thallium Imaging


This test uses a flexible fiber-optic video endoscope to permit visual examination of the lining of the large intestine. It's indicated for patients with a history of constipation or diarrhea, persistent rectal bleeding, and lower abdominal pain when the results of proctosigmoidoscopy and a barium enema test are negative or inconclusive.


  • To detect or eveluate inflammatory and ulcerative bowel disease
  • To locate the origin of lower GI bleeding
  • To aid diagnosis of colonic strictures and benign or malignant lesions evaluate the colon postoperatively reurrence of polyps and malignant lesions

Patient preparation

  • Tell the patient that this test permits examination of the lining of the large intestine.
  • Instruct him to maintain a clear liquid diet the evening before the test and to fast the morning of the procedure, according to the doctor's orders.
  • Describe the procedure, and tell the patient who will perform it and where. Inform the patient that the test usually takes 30 to 60 minutes.
  • Explain that the large intestine must be thoroughly cleaned to be clearly visible. Instruct the patient to perform the prescribed bowel preparation (for example, consuming Co-lyte, Fleet Phospho-Soda, or magnesium citrate) usually the night before the procedure.
  • Inform the patient that an I.V. line will be started before the procedure and that a sedative will be administered just before the procedure. Advise him to arrange for someone to drive him home because conscious sedation may affect his reflexes and reaction time, even if he feels fine.
  • Assure him that the colonoscope is well lubricated to ease its insertion, that it initially feels cool, and that he may feel an urge to defecate when it's inserted and advanced.
  • Explain that air may be introduced through the colonoscope to distend the intestinal wall and to facilitate viewing the lining and advancing the instrument. Tell him that flatus normally escapes around the instrument because of air insufflation and that he should not attempt to control it.
  • Tell him that suction may be used to remove blood or liquid stools that obscure vision but that this won't cause discomfort.
  • Check the patient's medical history for allergies, medications, and information pertinent to the current complaint.
  • Make sure the patient or a responsible family member has signed an informed consent form.

Procedure and posttest care

  • Place the patient on his left side with his knees flexed, and drape him.
  • Obtain baseline vital signs and leave the blood pressure cuff in place for monitoring during the procedure. Observe the patient's skin color, temperature, and dryness; abdominal distention; level of consciousness; and pain tolerance throughout the procedure.
  • Instruct the patient to breathe deeply and slowly through his mouth as the doctor palpates the mucosa of the anus and rectum and inserts the colonoscope.
  • The doctor inserts the lubricated colonoscope through the patient's anus and rectum into the sigmoid colon.
  • Assist the doctor as necessary in passing the colonoscope through the transverse colon, through the hepatic flexure, and into the ascending colon and cecum.
  • Abdominal palpation or fluoroscopy may be used to help guide the colonoscope through the large intestine.
  • Suction may be used to remove blood and secretions that obscure vision.
  • Biopsy forceps or a cytology brush may be passed through the colonoscope to obtain specimens for histologic or cytologic examination; an electrocautery snare may be used to remove polyps. A laser, Bicap, or Argon Plasma Coagulator may be used to treat areas of bleeding and polyps.
  • If the examiner removes a tissue specimen, immediately place it in a specimen bottle containing 10% formaldehyde; immediately place cytology smears in a Coplin jar containing 95% ethyl alcohol. Send specimens to the laboratory immediately.
  • Observe the patient closely for signs of bowel perforation. Report such signs immediately.
  • Check vital signs, and document them according to facility policy.
  • After the patient has recovered from sedation, he may resume his usual diet unless the doctor orders otherwise.
  • Provide privacy while the patient rests after the test; tell him that he may pass large amounts of flatus after insufflation.
  • If a polyp has been removed, inform the patient that his stool may contain some blood.
  • Although it's usually a safe procedure, colonoscopy can cause perforation of the large intestine, excessive bleeding, and retroperitoneal emphysema.
  • This procedure is contraindicated in patients who have ischemic bowel disease, acute, diverticulitis, peritonitis, fulminant granulomatous colitis, or fulminant ulcerative colitis.

CLINICAL ALERT Watch closely for adverse effects of the sedative. Have available emergency resuscitation equipment and a narcotic antagonist, such as naloxone, for I.V. use, if necessary.

  • If a polyp is removed but not retrieved during the examination, give enemas and strain stools to retrieve it, if the doctor requests it.

Normal findings

Normally, the mucosa of the large intestine beyond the sigmoid colon appears light pink-orange and is marked by semilunar folds and deep tubular pits. Blood vessels are visible beneath the intestinal mucosa, which glistens from mucus secretions.

Abnormal findings

Visual examination of the large intestine, coupled with histologic and cytologic test results, may indicate polyps, inflammation, ulceration, strictures, presence of a foreign body, granulomatous or ulcerative colitis, Crohn's disease, and malignant or benign lesions. Diverticular disease or the site of lower GI bleeding can be detected through visual examination alone.

Interfering factors
  • Fulminant colitis, peritonitis, acute severe diverticulitis, existing perforation, coagulopathy, and serious cardiac problems, such as unstable cardiomyopathy or recent myocardial infarction
  • Fixation of the sigmoid colon due to inflammatory bowel disease, surgery, or radiation therapy (may hinder passage of the colonoscope)
  • Blood from acute colonic hemorrhage (hinders visualization)
  • Insufficient bowel preparation or barium retained in the intestine from previous diagnostic studies (makes accurate visual examination impossible)
  • Failure to place histologic or cytologic specimens in the appropriate preservative or to send the specimens to the laboratory immediately
  • Patient's inability to cooperate or to physically tolerate the procedure

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