"It's all about plumbing"

From this entry, I will write down some operations that I saw in the OR. Let me start from some less complicated ones, e.g. colonoscopy.

Colonoscopy is a minimally invasive endoscopic examination of the large intestine. The endoscope goes through patient’s anus, and can go as far as to the cecum. Usually, the patient is lying on the surgical table and general anesthesia is given to the patient. At the first glance of the endoscope, there is nothing fancy. A black flexible tube and that’s it. But of course, it can’t be that simple. At the distal end of the black tube, a CCD camera is equipped to provide high definition motion pictures. The endoscope is also able to inflate the colon by blowing gas, so that the endoscope can move more freely and has a better view. In addition, it also has an injector and a sucker to clean up some small areas when that’s necessary.

The doctor held the tube on his left hand and gently pushed it, while his right hand was holding the control panel to adjust the angle of the distal end of the tube. He kept watching the monitor and searching any suspicious protrusions. “How can you tell up and down from the monitor?” The first question came suddenly. “Look at the water”. A resident successfully solved this quiz.

The above paragraph is a typical scenario I saw in a colonoscopy case. To me, colonoscopy is like an exploration of an unknown cave. You see many wrinkles on the wall. The CCD camera is your torch and eyes. The difference is that, instead of finding treasures, doctors are aiming at polyps. “It’s all about plumbing”. My doctor concluded after an operation. I couldn’t agree more.








A typical picture captured in a colonoscopy. From wikipedia, (http://en.wikipedia.org/wiki/Colonoscopy)

A little off topic!

I know I promised to continue writing about the issues around clinical trials, but I have also been observing some interesting radiological procedures and I would like to share them with everyone.
First I am going to talk a little about lung anatomy and then proceed to explain what could happen when you perform a lung biopsy. Imagine you push your fist into an inflated balloon. What happens is that you have one layer of balloon at immediate contact with your fist, and the rest of the balloon at immediate contact with the air outside. Between the two layers is the air "inside the baloon". The situation of the fist is analogous to how your lung is located inside the thoracic cavity. The balloon is called the pleura. Its layer in contact with the lung is called the visceral pleura, and the other one in contact with the thoracic cavity is called the parietal pleura. Between these two layers exists the pleural fluid which is what keeps the lungs inflated due to its surface tension. So now you may guess what happens if a needle gets into the pleural space. Air can enter this area (called pneumothorax) and the patient may very well get a collapsed lung. When a radiologist detect a suspisious nodule on a lung CT, and s/he thinks a biopsy is necessary, a fine needle will be inserted between the ribs, pass the pleural space and ultimately reach the nodule. In 25% of the cases the patient will get a pneumothorax, but 98% of them recover on their own. Meaning that the pleura recover on its own and lungs will be inflated (Note: the collapse is not due to the needle reaching the lung parenchyma itself, but the pleural space). However, in the remaining 2% (which includes people who are either very old or have other lung complications such as emphysema) the radiologist has to insert a tube in the lung and pump the lung back up. The tube is small, with a daimeter close to a spagetti nuddle.

Switching gears, I want to talk about some exciting interventional radiology, which is basically collecting images by insering catheders inside arteries and veins while patient is alert (minimally invasive with local anesthesia). Among the cases that I have observed, I think the most interesting one was IVC filter placement. IVC stands for inferior vena cava which is the major vein that carry de-oxygenated blood from legs and lower body to the right ventricle of heart. The filter is a little guy that looks like an umbrella without the cloth on top ofcourse and it is placed inside the vein to prevent entry of plaques and clots into the right ventricle and further blockage of pulmonary arteries which carry de-oxygenated blood to the lungs for oxygen exchange. The filter is shown bellow. The way the procedure works is that the interventional radiologist attach the hook of the filter to the catheder, and then insert the catheder in the femoral vein. There is sheath inside the filter that once pulled, makes it open up like an umbrella. When they inject the contrast and make sure that the filter is at the right place, they pull the cathder and sheath and make sure the filter is in place. It is interesting to know that you only feel pain on the surface of your skin and surface of the abdominal cavity. That's why if they place a catheder inside your veins and arteries you probably won't feel anything!

T1 Mapping

Thanks to Thanh for taking his time to explain to me what the purpose of the whole t1 mapping business, now I finally understand what the project is about and why we need it. Unlike CT imaging, in which the intensity can be described quantitatively as the attenuation of the x-ray source in Housefield unit, with conventional MR imaging techniques, the signal is relative, which differs from one image experiment to another and therefore cannot used for direct signal quantification.

The basic principle behind MRI is that each hydrogen protons (spin) in a system (such as hydrogen of water molecules in our body) will give rise to nuclear magnetization, all aligned in the same direction under an external magnetic field. If RF radiation at a specific frequency is applied to the proton magnetization, it will be perturbed from its original state. The system will then relax back to its equilibrium state. It is observed that this recovery process of the magnetization follows an exponential form and the rate at which the magnetization recovers is described by a time constant T1. MRI images intensity is proportional to this magnetization. Different tissues have different T1 values, so when we take an MRI image at a specific time after the RF pulse, the magnetization of different tissues will be different due to different recovery rate, hence creates contrast in an image. This is typically called a T1-weighted image since contrast is based on the difference of the T1 values.

The images above shows a conventional MRI image of the brain (T1-weighted) on the left and a T1 mapping of the same brain on the right. Images on the left will have different intensity values from one imaging experiment to another. However the T1 mapping on the right will be always the same for the same subject.

Although the intensity of an image is relative, but the T1 value creates this different in intensity is a quantitative characteristic of tissues and does not change from experiment to experiment. One way to obtain the T1 value is to record data points on the magnetization recovery process at each location. This can be done by taking MRI images at different times after the RF excitation. Then we fit all the data point at a specific location to an exponential model describing the signal recovery process as shown in the figure below. The data points are the intensity values of each image at the same location taken at different time after RF excitation.

Then, from this model we can obtain T1 value for a specific location. Since this involves a lot of calculation, it is only possible to calculate on specific points or region of interest (i.e the myocardium). My goal is to develop an imaging analysis tool, so the researchers can interactively select the location on the image they want and then it will perform all the necessary analysis automatically.

belated blog

Although it’s the fourth week, I still clearly remember the first day in the operating room.

One of the nurses warned me before I entered OR that some of the operations would be very gory. She also tried to make sure that I wouldn’t faint during observing and become the next patient in the emergency room. Another warning was do NOT touch anything, which was also what I wanted.

Actually, this was not the first time I was in the OR. But all the previous experiences are somewhat unpleasant because usually I was the one on the operating table. So I either had no mood to look around or I couldn’t remember anything after anesthesia. OR is more crowded than I expected. For a colorectal case, there are one major doctor, 2 to 3 residents, 2 to 3 nurses, and an anesthetist. If add some observers like me, there are almost 10 people surrounding the surgical table. Usually I stand next to the anesthetist, who sits at the head end of the surgical table and records the physiological signals. For some operations on the anal verge area, this is not the best place to observe, but for most operation on the abdomen, or laparoscopy, this is good enough to capture doctors’ every movement.

After the first day, I strongly feet that I need to build up some muscles on my leg if I want to be a doctor. A case can be last for several hours and doctors keep standing. Considering they also keep making decision in their mind, and cutting, stitching, I really appreciate their great effort for saving people’s life and enhancing patients’ quality of life.

Complications of surgery

Over the past few weeks, I’ve been on pre and post operative rounds as well as observing surgeries. The progression of the patient goes from diagnosis, tests, operation, to recovery. They’ll keep the patient over night to a few weeks to make sure they are stable and healthy to go home. But upon further reading case studies from my research and other operations, the patient is not always fixed and healthy many months or years later.

I’ve been reading case studies for esophageal atresia (EA) and tracheoesophageal fistula (TEF) and their post operative complications. I have also been comparing different eras to see if surgical techniques have improved in the last decade to minimize post operative complications.

In EA/TEF there are many complications after surgery. One are strictures which means a the intestinal tubes are narrowing. Another are anastomotic leaks when two tubes need are stitched together. Doctors may also miss a fistula which means the connection to the esophagus from the trachea remains. This of course makes it impossible for feeding and breathing to take place.

a stricture

Of these complications, I’ve found that surgical techniques over the past decade have not improved the overall rate for these complications to a significant value of 0.05. Even with the invention of vicryl sutures which can hold tension for several weeks and floseal which helps build a matrix over the tubes preventing leaks, post operative complications are still high. Many of these are easy fixes; for example, 1-2 dilations will help solve strictures.

Many of these doctors are trying to find better methods to perform these surgeries. They are also hoping for better technology to make their lives easier as well as preventing patient complications. I guess that’s where we come in.

Nuclear Stress Test

Patients that feel chest pain or any sort of discomfort that might be related to the heart are usually told to get a nuclear stress test done. There are a few different ways of performing a nuclear test, but in the end, they all asses the same thing - the distribution of blood in the heart. The test is not always necessary since there are apparently other ways of assessing a problem in the heart. For example, if a patient complains about chest pain, a doctor can take an EKG, notice a drop in the ST segments and then deduce that the patient probably had a heart attack. One could also underscore this claim with a blood test - looking for increased levels of troponin. The list goes on….

Fortunately, a nuclear stress test offers the clinician a quick way of assessing common problems in the heart. As a result, most patients with heart related problems will most likely have one done. The idea is simple; inject the patient with a radioactive isotope, thalium201, which gets concentrated in the tissues of the heart receiving blood supply. Then use a gamma scintillator camera to read the signal from different angles of the body. In the end, the doctor receives a low spatial resolution image that depicts portions of the heart that receive less blood as dark spots while others that receive a lot of blood as bright spots (figure).




Unfortunately, the signal detected by the gamma scintillator camera is not calibrated to an absolute scale. In fact, since the signal is relative, the doctor cannot say much if he observes dark spots in regions of the heart where one would intuitively expect bright spots. Evidently, one can claim that the dark spots are due to below normal levels of perfusion while someone else can claim that the dark spots are normal since the bright spots are due to above normal levels of perfusion. Partially for this reason, after obtaining images of the heart at rest, the patient is told to exercise, so that the blood supply can be maximized at all portions of the heart. For patient’s that can’t exercise, the alternative is to be injected with a vasodilator (dipyridamole (Persantine), adenosine (Adenoscan), or dobutimine). Shortly following, the patient is injected with another isotope, Technetium -99m pyrophosphate or Mibi, in the case of a dual isotope scan. Each isotope peaks at a different energy level (in keV) so the two are easily filtered and thereby differentiated. In terms of differentiating between the two sets of images (one at rest and the other under stress), one must rely on a little nuclear physics. The radiation emitted by mibi is usually stronger and scatters less; thus, the spatial resolution of the set of images of the heart under stress is usually better. Furthermore, mibi is filtered by the body differently form thalium. So another way of differentiating between the two sets of images is to see where they are concentrated in the human body; typically either the kidneys or the gall bladder.

Anyway, the images of the heart at rest and under stress make the claims about the distribution of blood in the heart more plausible. They can help the doctor identify coronary artery disease or other potential anomalies in the heart. Yet, this imaging modality can use some improvement. I used to wonder why it was not possible to integrate the resolution of CT with the perfusion identifying capabilities of a NST. Fortunately, I recently discovered that there has been some work underway on this and one might see a device/software that does just that in the near future.

My time in the MICU

This past week I spent most of my time in the Medical Intensive Care Unit (MICU). While I was there, I got to do rounds for the first time (everywhere I have been thus far don't generally do rounds), which was interesting. I got to hear residents, medical students and attendings discuss patients and treatment plans, and was amazed at how much they can have memorized at any given time.
While there I also got to here about how a diabetic who comes into ER for volume depletion and hyperglycemia (to much sugar in the blood) can be brought from the brink of death (seriously) to outpatient status in less than a day. This seemed to make the attending very happy/excited. He explained that even though one would think that giving insulin would be the first thing to do (to push the sugar into the cells), since the patient was volume depleted, and the volume depletion is part of the source of the hyperglycimia (remember reduced volume=increased concentration), it would be one of the worst things you do (since the sugar will take water with it as the sugar moves into the cells, making the volume depletion worse/fatal). He said first you stabilize the airways and then give saline (to up the circulatory volume), and THEN you give insulin. BAM! And the guy can go home the next day.

Also while I was there I got to witness an interesting procedure that serves as the solution to a problem I had only ever seen in radiology CT images prior to that day. The problem: plueral effusions (liquid in the chest cavity). The solution: Poke a hole and drain it (simple, no?). See, normally the lungs fill the chest cavity with the surface of the lung literally attached to the surface of the thoracic cavity (left image, medicalimages.allrefer.com). However sometimes fluid builds up in the cavity and pushes on the lung which can make it difficult to breathe. Especially when the amount approaches a full litre. The schematic (bottom left image, medicalimages.allrefer.com) and how one looks in a CT scan can be seen (bottom right image, http://www.ispub.com/xml/journals/ijra/vol4n1/merkel-fig1.jpg) can be seen below. But basically, the solution is literally poke a hole and suction out the fluid by hand (kind of like a bilge pump).














Finally, I heard an interesting talk on two case studies from patients in the MICU. One of the patients has cystic fibrosis, and the discussion went on to discuss the epidemiology of the disease. Since I want to possibly go into public policy after getting my degree, epidemiology is an interesting topic for me. Briefly, cystic fibrosis is a genetic (autosomal recessive) disease that leads to progressive disability and eventually death. The genetic mutation effects the creation of chloride channels, effectively creating channels with a lower conductance. This
The interesting part of the discussion is when the attending leading the talk began discussing how genotypes persist for reasons. An example of this logic is how sickle cell anemia primarly affects populations at risk for malaria and the former grants a certain level of resistance to the later. So the attending asked

"What disease's effects would be reduced by the reduction of chloride channel conductance?"
Here are the hints:

1. Third World Disease
2. Remember: Chloride channel conductance reduction => decreased fluid loss
   
3. GI Tract

Answer: Cholera! If you can't lose the ions, you can't lose the water, and therefore you can't dehydrate.

Now that was a cool excercise in logic.